Confidence,SecurityVerification

&

“Deterrence, arms control &proliferation are criticallyimportant to Britain’s security”[1998 Strategic Defence Review]

The challenge of global nuclear weapons arms control

page 2

Contents

Contents 2Title page 3Summary 4Introduction 8Warhead authentication 12Introduction 12Non-destructive assay 13Non-destructive radiometric techniques fornuclear warhead authentication 15NDA techniques as applied to generic warhead designs 18Discussion 20Dismantlement and disposition 22Introduction 22Treaty context 22Signature measurements and comparisons forverifying the dismantlement process 24Baseline signature requirements 25Confidence in dismantlement verification 27Dismantlement facility surveillance 28Disablement and demilitarisation 29Disposition 30Nuclear weapon infrastructure control and dismantlement 31Discussion 31Monitoring the nuclear weapon complex 32Introduction 32Environmental monitoring overview 33Environmental monitoring application 34Discussion 36Proposed arms control verification research programme 38Creation of a focus for verification research 38Outline programme 39Discussion 41Threat Reduction perspective 42Introduction 42A focused mission 43Interfaces 43Conclusions 44Acknowledgements 45Appendix A -Radiometric non-destructive assay 46Passive non-destructive radiometric techniques 46Active non-destructive radiometric techniques 49Appendix B - Nuclear warhead components 52Appendix C - Radiation signatures 54Appendix D - Sources 55Appendix E - Glossary 56

page 3

Title Page

Reference AWE/TR/2000/001

Title Confidence, Security and Verification: The challenge of global nuclear weapons arms control

Sponsor This paper has been prepared for the United Kingdom Ministry of Defence (AD(Sci)/Nuc 2 and AD/MR(Nuc)), within the Nuc32B/30014 Project Contract.

Abstract This paper presents initial AWE work directed at providing Her Majesty’s Government with a national capability to contribute to the verification challenge resulting from any future global nuclear weapons arms control negotiations. The work responds to tasking identified in the 1998 Strategic Defence Review and by design has been biased towards the value of scientific and technical tools, especially radiometric non-destructive assay and radiochemical analysis, in answering the verification challenge presented at the warhead and system level.Also the paper presents verification in the context of a broader national security mission, related to minimising the global threat of nuclear weapons, and addressing the proliferation of related knowledge and associated materiel.

Authors This paper has been produced by a team composed of senior scientists andengineers from AWE: Christine Comley, Mike Comley, Peter Eggins,Garry George, Steve Holloway, Martin Ley, Paul Thompson, Keith Warburton.

The opinions expressed here are those of the authors and do not necessarilyrepresent the views of the MoD.

Information Further information on this paper and the emerging nuclear weapons armscontrol and warhead reduction verification research programme at AWE may be obtained from Garry J George at AWE (Garry.George@awe.co.uk) or at http://www.awe.co.uk.

Atomic Weapons EstablishmentAldermastonReading, Berkshire. RG7 4PR

page 4

Summary

In July 1998 the Secretary of State forDefence in the Strategic DefenceReview (SDR), stated:

“The effectiveness of arms controlagreements depends heavily onverification. The United Kingdomhas developed particular expertisein monitoring of fissile materialsand nuclear tests. We plan to addto this by developing capabilitieswhich could be used to verifyreductions in nuclear weapons,drawing on the expertise of theAtomic Weapons Establishment atAldermaston. This will begin witha study lasting some 18 months toidentify the technologies, skillsand techniques required and whatis available in this country.”

The study identified in the SDR wasdirected through the Ministry ofDefence’s Chief Scientific Adviser.

The Secretary of State for Defencestated further in the SDR that“Deterrence, arms control andproliferation are criticallyimportant to Britain’s security”.The UK and the other States Partiesto any future Treaty aimed at reduc-ing or eliminating nuclear warheadswill need to be positively assuredthat a robust verification regime is inplace. They will need high confi-dence that warheads are being dis-mantled and at the same time thatwarheads are not being concealednor produced outside agreed Treatylimits.

Although arms reduction steps havebeen made at the bilateral levelbetween the US and Russia, thechallenge of approaching warheadreductions at the multilateral andglobal levels we consider to be more

complex, especially as warheadstockpiles approach very low levels.Any multilateral Treaty will requirecoupled technical and diplomaticsolutions to ensure that there isappropriate national andinternational confidence. In otherwords that the risks are reduced toacceptable levels.

A scientific and technicalunderstanding of verification, andthe associated levels of confidencethat may be realised, is thusconsidered to be a logical precursorto realising a future multilateralnuclear weapons arms controlTreaty. The study phase,summarised in this paper, hasidentified a technical route for thecost-effective development of UKtechnical verification capabilities tosupport HMG’s Strategic DefenceReview commitments to globalnuclear weapons arms control.To realise a robust global warheadreduction verification regime webelieve it will be necessary to ensurethat:

4 warheads are not added to thestockpile beyond any agreed level (Accountancy)

4 there is a suitable stockpile chain of custody established forwarheads entering dismantlement (Provenance)

4 warheads presented for dismantlement are validated (Authentication)

4 dismantlement is asirreversible as possible (Disposition)

page 5

Authentication of warheadsand warhead components sitsat the centre of the challengeof how to verify warheadreductions. Authenticationmight be obtained from anumber of non-destructivemonitoring techniques. Theaim of these techniques is toobtain information about thetype, quantity anddistribution of materialswithin a ‘package’ (a warheador containerised warheadsystem), without opening thepackage, damaging thecontents or compromisingproliferation and nationalsecurity concerns.

Although the authenticationprocess will help determine,to within a defined level ofconfidence, whether thepackage contains a legitimatenuclear warhead or sub-assembly, or is part of adeception process, it will notnecessarily answer thequestion: “does the warheadcome from the stockpile beingreduced?” Information from awider nuclear weapons armscontrol regime will berequired to answer thisprovenance question.

From the work undertaken inthis study phase it isconsidered that radiometricnon-destructive assay (NDA)measurements conducted onplutonium-based, single-stagenuclear warheads can providequantitative information onfissile material and some ofthe surrounding non-nuclearmaterials. The accuracy of

quantitative informationobtained from radiometricNDA measurement, however,decreases with increasingcomplexity of warheaddesign, for instance with atwo-stage thermonucleardesign.

Therefore within a globalTreaty context, with manywarhead configurations andthe probability of incompletedesign transparency betweenStates Parties, it is notconsidered likely thatauthentication by radiometricassessment alone will berobust enough. Radiometricmeasurements of an item may,however, provide support toan authentication assessmentprocess using multipletechnical and administrativedata sources, using so-called‘data fusion’ techniques,although there will be acontinuing need to addressproliferation and nationalsecurity concerns.

Once a nuclear warhead hashad its provenance confirmed,been authenticated and had abaseline signature establishedit could be tracked through adismantlement process usingcomparative radiometric non-destructive signaturemeasurements alone. The useof ‘information barriers’should prevent nuclearwarhead design informationbeing revealed beyond a‘trusted’ community.Therefore controlling andminimising the risk ofproliferation.

The number of operationalwarhead configurations thatmay be deployed in a StateParty’s stockpile is large andhence, without appropriatetransparency, there will beuncertainty regarding thenature of the warhead designbeing offered for reduction aspart of a global Treaty. It istherefore consideredimportant that before anyTreaty enters into force,warhead designs and/orsignatures applicable to thatTreaty be understood for theirimpact on verificationconfidence.

In addition to non-destructiveassay, environmentalmonitoring (EM) is seen as acomplementary backgroundprocess to the potentiallymore design-intrusivewarhead focusedauthentication processes. Theenhanced IAEA Safeguards,introduced following the GulfWar, illustrate the potentialvalue of EM as a means oftesting for the presence ofmaterials that are likely to beemitted by warheadproduction facilities.

Although environmentalmonitoring will not by itselfsupport warhead reductionverification, it is consideredan important process forproviding supportingevidence that a State Party isnot involved with illicitwarhead activity outside ofany Treaty agreement. Thisintegrated view of global armscontrol and reduction

page 6

verification becomes evermoreimportant as the numbers ofwarheads reduce towards zero.

The AWE work carried out thus farhas established a foundation onwhich we intend to investigate thepotential of wider UK capabilities, inorder to understand better anddevelop further a true nationalcapability directed at the challengeof global nuclear weapons armscontrol. During the study phase wehave made contact with potentialnational partners within UKacademia and industry, with whomwe intend to engage during theresearch phase.

Achievement of a verifiableinternational Treaty in isolation,however, would only address part ofthe global vulnerability posed bynuclear warheads and nuclearweapons of mass destruction. It isimportant to see verification andverification research as part of awider national security mission,which includes deterrence andcomplementary national securityThreat Reduction programmes.

The Threat Reduction perspectiveencompasses: threat andvulnerability analysis; export andother proliferation control;verification of international treatiesand national material managementcontrols; and crisis/consequencemanagement (emergencyinterventions when vulnerabilitymanagement and controls have beencompromised).

We believe the Threat Reductionprogramme we have identified inthe study phase will create a morecoherent nuclear warhead national

security mission at AWE, aimed atmeeting the challenge presented byglobal nuclear weapons armscontrol, warhead non-proliferationand crisis/consequencemanagement. We haverecommended to the MoD aprogramme of research into armscontrol verification as part of AWE’senduring Threat Reductionprogramme.

In conclusion, in the study phase ofour work we have considered theUK’s capabilities and identifiedtasks for the first, or foundation,year of a three-year researchprogramme directed at technicallysupporting Her Majesty’sGovernment’s policy on nuclearweapons arms control. We haveproposed that this work be focusedthrough a Verification ResearchProgramme, which in turn will bealigned with other aspects of AWE’swider Threat Reduction programme.

page 7

page 8

In July 1998 the Secretary of State forDefence in the Strategic DefenceReview (SDR), stated:

“Deterrence is about preventingwar rather than fighting it. All ourforces have an importantdeterrent role but nucleardeterrence raises particularlydifficult issues because of thenature of nuclear war. TheGovernment wishes to see a saferworld in which there is no placefor nuclear weapons. Progress onarms control is therefore animportant objective of foreign anddefence policy. Nevertheless,whilst large nuclear arsenals andrisks of proliferation remain, ourminimum deterrent remains anecessary element of our security.

“The effectiveness of arms controlagreements depends heavily onverification. The United Kingdomhas developed particular expertisein the monitoring of fissilematerials and nuclear tests. Weplan to add to this by developingcapabilities which could be used toverify reductions in nuclearweapons, drawing on theexpertise of the Atomic WeaponsEstablishment at Aldermaston.This will begin with a study lastingsome 18 months to identify thetechnologies, skills and techniquesrequired and what is available inthis country.”

The study identified in the SDR wasdirected through the Ministry ofDefence’s Chief Scientific Adviser.This paper reviews as much of thestudy phase’s work as possible.Matters of proliferation sensitivitywill, by necessity, mean that someissues can not be included.

Although this paper focuses on thetechnical aspects of verification, the‘political context’ has not beenignored in the study. The issues, bydefinition, are complex and part ofthe future work will be the need toaddress the links between the ever-evolving diplomatic ideas anddevelopments associated with globalnuclear weapons arms control, andthe emerging technical verificationresearch programme. For example,the impact on verification oftransparency and confidencebuilding agreements.

It is intended that research links beestablished with potential partners,including Non-GovernmentOrganisations (NGOs), especiallythose with a strong UK base. Thepurpose is twofold. First, it willallow a bridge to be formed betweenAWE’s warhead biased work andother communities withcomplementary scientific andtechnical experience. Secondly it willprovide an extended network fortesting verification ideas and toolsthat, in the end, need to be usable aspart of a diplomatic solution.

The Secretary of State for Defencestated further in the SDR that

“Deterrence, arms control andproliferation are criticallyimportant to Britain’s security”.

Recognising this integratedperspective will be essential if aglobal nuclear weapons armscontrol� Treaty is to be achievedwithout compromising nationalsecurity concerns.

The UK and the other States Partiesto a future Treaty will need to be

Introduction

page 9

positively assured that arobust verification regime is inplace. They will need highconfidence that warheads arebeing dismantled and at thesame time that warheads arenot being concealed norproduced outside agreedTreaty limits. The issuespresented by this globalverification challenge isconsidered to be morecomplex than those faced bybilateral (eg US-Russia)verification regimes biasedtowards large warheadnumber and delivery systems.We therefore believe there willbe a need for integratedmultilateral technical anddiplomatic solutions to ensurethat there is appropriateglobal confidence. In otherwords that national andinternational risks are reducedto acceptable levels.

Despite its deterrent role, it isaccepted that no verificationregime could possibly bedevised to provide 100%confidence in its effectiveness;some residual risk mustremain. The higher therequired confidence, the moreexpensive and invasive theregime, and, crucially, thehigher the degree of co-operation or transparencybetween the States Parties toany Treaty will need to be.

In order that the UKappropriately addresses thechallenge of Treatyverification, the SDRsupporting essay number fivestates that “a small team will

be established [at AWE] toconsider technologies, skillsand techniques, and toidentify what is alreadyavailable to us in the UnitedKingdom. ... The aim is toensure that, when the timecomes for inclusion of Britishnuclear weapons inmultilateral negotiations, wewill have a significantnational capability tocontribute to theverification process”.

We believe that understandingthe technical context andlegacy of the past 50 years isan important part of achievinga verifiable global Treaty anda robust global non-proliferation regime.Therefore, one of the tasksidentified in our future workis to make use of the UKnuclear warhead programmearchives. This will provide afoundation for understandinghow historical information,some of it proliferationsensitive, may be used as partof any transparency andconfidence building dialoguewith other States at a futurenegotiating table, or as part ofa Treaty verification process.For example, the SDRannounced process ofpublishing information on thefissile material used in theUK’s defence nuclear pro-gramme.

Not all Nuclear Weapon States(NWSs) have followed thesame path in their technicaldevelopments. There is nosuch thing as a singlewarhead design, even for a

plutonium based implosionsystem. The complication ofcarrier vehicles andtransportation systems merelyadds to the complexity of thesituation. Verificationtechniques, systems andinterventions all need to beunderstood within a globaland/or multilateral context.Solutions based on nationalperspectives will not besufficient.

The Canberra Commission(reference 16) observed that“a political judgementwould be needed as towhether the levels ofassurance possible from theverification regime aresufficient.” Such judgementsneed to be made within aframework, devised by, andfor the benefit of, theindividual States Parties toany Treaty. It will therefore beimportant to understand, apriori, the possible concernsand goals of all States Partiesin order to formulate realisticUK policies, underpinned bytechnical capability, that donot undermine the goal ofverifiable global arms controlof nuclear warheads.

The Secretary of State forDefence’s statements in theSDR that “The Governmentwishes to see a safer worldin which there is no placefor nuclear weapons.” re-emphasises an internationallyrecognised goal that has beenin existence for over fiftyyears. More recently it hasbeen articulated through the

page 10

Comprehensive Test Ban Treaty text,which states:

“the need for continuedsystematic and progressive effortsto reduce nuclear weaponsglobally, with the ultimate goal ofeliminating those weapons, and ofgeneral and complete disarma-ment under strict and effectiveinternational control.”

Progress on nuclear weapons armscontrol has of course been made: forinstance the Intermediate NuclearForces (INF) Treaty and theUS/Russian Strategic ArmsReduction Treaty (START) process.START I (1991) and II (1993) haveled the way to the current START IIItalks, where Presidents Clinton andYeltsin reached bilateral agreementin principle following their 1997meeting in Helsinki. The START-IIITreaty, if realised, would mandatestill deeper cuts in US and Russiannuclear arms and establish a new setof bilateral nuclear transparency andconfidence building measuresbetween the US and Russia, directedat warheads and not just deliverysystems.

Whilst the current warheadreduction negotiations are restrictedto strategic systems and do notaddress the warhead authenticationchallenge that exists in a globalcontext, there are many benefits tobe gained in understanding thelessons learned thus far. Also there ismerit in understanding the lessonsassociated with the various non-nuclear treaties, for instance theChemical Weapons Convention.Understanding such lessons will bean important part of realising arobust nuclear weapon global

(multilateral or international) Treaty.We believe that knowledge andexperience sharing across treatiesshould be a strong element of anyfuture research programme.

The AWE Study provides a first steptowards identifying the UKcapabilities needed to supportHMG’s policy directed towardsachieving verifiable global nuclearweapons arms control. Theverification technologies that mostdirectly support warhead reductionsare those aimed at non-destructiveassay (NDA) and evaluation, for thepurpose of authenticating warheads,and tracking warheads, warheadcomponents and residues throughdismantlement and materialdisposition processes.

Additionally, environmentmonitoring (EM), which may befocused towards Treaty verificationof a State Party’s weapon complexor identifying the clandestineproduction of warheads outside ofany Treaty regime, also needs to berecognised. The NDA and EMtechnologies act together, one in theforeground and the other in thebackground. Thus allowing a robustand verifiable Treaty regime to berealised that addresses warheadreductions within a global warheadcontrol regime.

Verification research is, however,only part of a broader nationalsecurity objective. In the study wehave used the term ThreatReduction to encompass: threat andvulnerability analysis; export andother proliferation controls;verification of international treatiesand national material managementcontrols; and crisis/consequence

page 11

management (emergencyinterventions whenvulnerability managementand controls have beencompromised).

Finally, in the main sectionsthat follow we discuss thevarious areas that will formkey elements in the proposednuclear weapons arms controlverification researchprogramme and place them inprogramme context:

Authentication of warheadsand warhead components is atthe centre of the globalnuclear weapons arms controlverification challenge.Deciding that a warheadoffered for reduction is what aState Party declares it to be,will be one of the most criticalaspects of any Treaty.

Dismantlement discusses theverification issues that mayarise following thewithdrawal of a nuclearwarhead from the stockpileand its entry into a dispositionchain.

Monitoring the nuclear weaponcomplex reviews existing andemerging technologies, skillsand techniques that may beused to establish the existenceand/or the status of a StateParty’s nuclear weaponsprogramme.

� In this paper the term ‘global arms control Treaty’, or Treaty for short, is used to embracethe many potential paths that exist in reaching the ultimate goal of the global elimination ofnuclear weapons. As the prime purpose of this paper is to present discussion on the scientificand technical tools that may be used to verify any Treaty directed at globally reducing nuclearWeapons, only passing reference will be made to the many political and diplomatic scenariosand future chronologies that may exist. Finally, for simplicity, the terms weapon and warheadare used in an interchangeable fashion in this paper.

Proposed verification researchprogramme captures theproposed outline programmeof the first year’s researchphase (1st April 2000 to 31stMarch 2001).

Threat Reduction perspectiveplaces the nuclear weaponsarms control research work inits national securityperspective, as part of acoherent capability tounderstand and address thethreat to the UK of nuclearweapons, their knowledgeand materiel. The ThreatReduction mission creates aclear focus to ensure anational science andtechnology capability toaddress the challenge ofrealising robust global nuclearweapons arms control andnon-proliferation regimes.

page 12

Introduction

Authentication of warhead andwarhead components is at the centreof the global nuclear weapons armscontrol verification challenge.Warhead authentication, establishingthe provenance of a warhead, andmaintaining an appropriatedismantlement chain of custody weconsider to be three of the mosttechnically challenging verificationprocesses of any potential Treaty.

During the study phase we adopteda simple framework to help developideas. The diagram below illustratesthis framework and shows that theprocess of maintaining warhead andcomponent control (accountancy)and authenticating a warhead is akey Treaty intervention which willneed to be integrated with thelegitimate stockpile manufacturing,storage, deployment, refurbishmentand disassembly processes of a StateParty.

The framework assumes two distinctbut related aspects to realising arobust verification regime: first, anoverarching arms accountancy andcontrol environment that operates atthe integrated weapon complex

level; and secondly, a warheadreduction process that operateswithin the overall nuclear weaponsarms control environment.Although, at this stage, we have notaddressed the detailed systems levelinteractions between these twoaspects, and the verificationinterventions that may be jointlyapplicable, this is an area we intendto study in the research phase. Thereis, however, already useful thinkingon the matter of realising a nuclearweapons arms control environment.For example, in the study phase wehave adapted some of the ‘NewCourt’ ideas of Robert Rinne(reference 18), who has identified apotential nuclear weapon controlregime.

This chapter discusses the assistanceto verification that can be obtainedfrom a number of non-destructivetechniques�. The aim of thesetechniques is to obtain informationabout the condition, type, quantityand distribution of materials withina ‘package’ (a warhead orcontainerised warhead system),without opening the package ordamaging the contents. Theinformation obtained will help todetermine whether the package

Warhead Authentication

Warhead & ComponentControl & Authentication

Material Storage& Disposition

On-SiteInspections

Safeguards

Manufacture,Refurbishment& Disassembly

Environmental Monitoring

Non-Destructive Assay

Arm

s C

on

tro

l & R

edu

ctio

nV

erif

icat

ion

Reg

ime

StockpileTransportation,

Storage & Deployment

page 13

contains a credible nuclearwarhead and, if so, providesome information about thematerials, especially the fissilematerials, to help establish achain of custody baseline fordismantlement and disposi-tion.

Non-destructive assay

Radiation monitoringtechniques form aconsiderable part of the non-proliferation technologies thatnow exist. Numeroustechnical publications onradiation detection andmeasurement issues have seentheir way into the widerworld through, for example,open conferences, symposiaand journals organised andpublished by the Institute ofNuclear MaterialManagement (reference 12)and European SafeguardsResearch and DevelopmentAssociation. As part of thestudy phase a national surveyhas been carried out, whichhas identified areas oftechnical competence andinterest within the UK. In theresearch phase we intend tobring these interestedcommunities together andexplore potential partnerships.

Many radiation detectiontechnologies are applied dailyas part of AWE’s routinebusiness to ensure the safecontrol and accountancy of itsfissile material stocks,processes, process residuesand wastes. Although otheragencies apply similartechnologies, AWE’s use of

these technologies in awarhead environment isunique in the UK. Also anumber of the technologiesare used as part of AWE’scrisis/consequencemanagement commitment toMoD.

There are three reasons whyNDA may have a role as partof a verification regime of aTreaty:

4 First, there is a need toverify the authenticity of Treaty declared warheads, including, potentially, those operationally deployed. For instance to verify declared numbers as part of a nuclear weapons armscontrol regime.

4 Secondly, radiation-based NDA techniques canprovide some vital information about nuclear materials much more quickly, cheaply and safely than chemical or radiochemical analysis.

4 Thirdly, these techniques, being (potentially) non-intrusive as well as non-destructive, may, by the use of appropriate information barriers, lead to verification without revealing national security or proliferation sensitive designinformation, which the State Party being verified may prefer to protect.

During the study phase workfocused on the use that can bemade of various radiationsignature types and their

combinations to assistverification confidence, ratherthan on the range of availabledetector technologies andhardware, which is vast.However, it is acknowledgedthat there are new detectortechnologies becomingavailable all the time. Theirpotential roles in theverification process, as well asthe potential roles of other UKagencies, will be ascertainedthrough collaborativepartnership as part of theresearch phase.

There are two basic classes ofNDA radiation monitoringtechniques:

Passive techniques. These relyon the fact that all nuclearwarheads (NWs) containradioactive materials that emitgamma and neutron radiation.Some of this radiation willescape from the warhead andmaybe be available fordetection. By appropriatemeasurements of theseradiations, valuabledeductions can be made aboutthe type and quantity of theradioactive materials. Inaddition, the radiation mayinteract with normally non-radioactive materials withinthe warhead, cause them tobecome radioactive and emitradiation. This activationradiation is often detectableand thus deductions can bemade about the type andquantity of the materials thathave been activated. Usuallyit is neutron radiation thatcauses activation. Theresultant emissions areusually gamma radiation.

page 14

Active techniques. This, second classof non-destructive radiationmonitoring techniques, uses anexternal source of radiation to causeactivation and fission in warheadmaterials. This class of techniques isparticularly useful for the assay ofthose warheads, or parts ofwarheads, in which the materialsemit insufficient radiation fordetection naturally. Also, an externalsource may be tailored, up to apoint, in terms of type, energyspread, intensity, duration anddirection. Such tailoring mayenhance the value of some results.However the technique does notlend itself to absolute quantitativemeasurements because the quantityof detected radiation, unlike inpassive techniques, is not directlyrelated to the quantity of material.

Appendix A provides backgroundinformation on both active and pas-sive NDA. It illustrates how thesetechniques may be used to estimatethe total fissile material content of anitem. For example, by applying highresolution gamma spectroscopy(HRGS) to determine a set ofplutonium (Pu) isotopics for anunknown item and combining the

data with the measured responsefrom, say, a neutron coincidencecounter. The coincidence counterresponse is itself a complex functionof the isotopic composition of thePu, and only from a knowledge ofthe HRGS-derived isotopic data canthe coincidence counter response beconverted to a total fissile mass.Thus, together, and only together,will some of the individual NDAtechniques be of any value as part ofa verification process.Although the NDA basedauthentication processes will helpdetermine whether or not thepackage contains a credible nuclearwarhead or sub-assembly, or is partof a deception process, it will notanswer the question: “does the war-head come from the stockpile beingreduced?” Information from a widernuclear weapons arms controlregime will be required to answerthis provenance question.

Authentication will only provideevidence that a nuclear warhead’s(NW’s) signature is consistent (ornot inconsistent) with that of a givenclass of NW. It will therefore benecessary to augment theauthentication process with other

NDADetector

NeutronSource

ActivePassive

page 15

(ideally) transparent stockpileevidence.

Any lack of transparency maybe schematically seen as apartial barrier, or fog, to theindividual contributionsnecessary to achieve effectiveverification. The level oftransparency associated withinformation is thus a criticalaspect to realising a robustverification regime.

Non-destructiveradiometric techniquesfor nuclear warheadauthentication

In the process of tracking aNW through dismantlementto its final disposition, thequestion arises; can it beproven, by the application ofradiation detection,measurement and evaluationsystems (ie NDAtechnologies), that:

4the item presented fordismantlement is an authentic NW and not a NW case containingvarying proportions of ‘real’ and substitutecomponents forming a ‘hoaxed’ NW, and

4 the elimination of the NW (and its components) can be verified by sufficiently rigorous NDA assessment prior to, during, and after the dismantlement?

Given that the most importantcomponent in a NW is thefissile material, in the form of

plutonium, highly enricheduranium (HEU) or otherenrichments of uranium, it isconsidered that a large part ofthe verification process mustfocus heavily uponestablishing whether materialsubstitution has taken place.

“[The] ‘provenanceprinciple’ illustratesthe importance ofaddressing armsreduction as part of atransparent armscontrol regime”

If the authentication of a NWcannot be established by theapplication of NDA then theNW dismantlement trackingprocess (through to finalfissile material disposition)must commence at a pointwhere there is at least a veryhigh confidence that the itemspresented are bona fide NWs.It is considered that thisstarting point coincides withdeclared stockpile storagelocations from which NWs arenormally despatched, either totheir intended delivery systemor returned to an assemblyfacility for maintenanceand/or refurbishment. At any

other point in the NWlifecycle there is increasingopportunity for materialsubstitution to take placethereby diminishing overallverification confidence. This‘provenance principle’�illustrates the importance ofaddressing arms reduction aspart of a transparent nuclearweapons arms control regime. The fundamental issue to beaddressed is to what extentcan the range of passive andactive NDA techniquesdiscussed in this paperindependently confirm anitem as being an authenticNW. That is with whatconfidence will theassessment yield a “yes or no”answer.

Before examining this issue,however, it is important torecognise that NDA willimplicitly identify specificNW design data (e.g. SpecialNuclear Material (SNM)�types, associated quantities,etc.) and that action may haveto be undertaken to protectand limit this data due tonational security orproliferation sensitivity.Herein lies the main challengepresented by NDA.Authentication (defined ashigh confidence that the item

VerificationTechnology

VerificationRegime

Declarations

SignatureBaseline

Provenance

Transparency

page 16

presented is a NW or its signature isconsistent with that of a credibleNW) requires access to a range ofabsolute data values in order tomake a credible assessment. Thosequantities themselves, however, maybe classified or sensitive to a StateParty.

It is thus worthwhile consideringwhat can be achieved with regardsto data protection that still permits aviable verification process, but doesnot make this information availableto the inspector conducting theNDA measurement(s) or to anypotential challenge State Party.Moreover, it is important toascertain that the issue of necessarydata protection will not preclude theuse of any of the potential NDAtechniques.

“Authentication requiresaccess to a range ofabsolute data values inorder to make a credibleassessment, but thosequantities themselves maybe classified or sensitiveto a state party”

Non-nuclear techniques for nuclearwarhead authentication�

It is important to recognise thationising radiation is not the onlyattribute that may be exploitedduring verification. Various physicalproperties could be used; forexample the ‘temperature’ of thedevice as measured by infraredimaging. Actinide radioactivematerials emit enough energy to bemeasurably warmer than thesurroundings. Also acousticresonance spectroscopy (ARS) is a

state of the art technique for non-destructive evaluation (NDE)monitoring. It also has someverification pedigree, having beenapplied to chemical weapons armscontrol. ARS overcomes many of thelimitations of other acoustic basedNDE methods. By extending thefrequency band to includefrequencies below ultrasonic, ARScan measure large-scalecharacteristics of an object. Byemploying a swept frequencyexcitation in lieu of a pulse, ARS canmeasure the resonance spectrum ofan object with high precision. Thesetechniques, together with others,such as modal signature analysis,could be used to confirm awarhead’s status, as long as physicalaccess is permitted. The researchphase will consider a full spectrumapproach to the question of NDAbased authentication, bothradiometric and non-radiometric.

Data protection requirements

The conflict between high-qualityverification and the risk ofproliferating sensitive informationthrough intrusive measurements hashistorically been addressed by the

NuclearWarhead

page 17

use of low-resolution sensors(e.g. Sodium-Iodide (NaI)-based gamma-ray detectors)which blur or decrease spec-tral detail, thereby reducingtransfer of sensitive data.However, such techniquespotentially also lead to low-confidence verification. Forexample, standardcommercially availableradioactive sources can beused together to simulate atypical Pu gamma-rayspectrum as observed by NaIspectrometry and couldtherefore provide the basis fora hoaxed NW. In addition, theuse of a suitable neutron-emitting source provides theexpected spontaneous fissionneutron output from thehoaxed ‘Pu’ device, such thata crude neutron detectioncapability (i.e. operating intotal neutron counting modeonly) would fail to distinguishfrom real Pu.

One way in which highquality, reliable informationavailable from high-resolutionsensors could still be used,without the possibility ofinadvertent disclosure, is touse a suitable computer toacquire and analyse the data.This approach would usealgorithms that evaluate thevalidity of the data, butdisplay only the outcome ofthe evaluation to the inspectorwithout ever revealing any ofthe data on which theconclusion is based. Thecomputer could also beprogrammed to automaticallypurge any data followingauthentication.

The data itself could beabsolute in form (i.e.quantitative having appliedthe appropriate measurementresponse factor for the NDAtechnique) or stored as rawcounts. The evaluationprocess could be based on thecomparison of such rawmeasurement data againststored data from a previousmeasurement of the item (aswould be undertaken in theitem-tracking mode ofverification). Alternatively,data from items of the sametype and with verifiedprovenance might be used toaccept a warhead as genuine.Finally, the issue ofproliferation sensitivity mayindicate that certain storeddata, or ‘templates’, may needto be kept under joint or‘trusted’ custody to precludecompromise of the data.

The reader should be underno illusions that dataprotection solves thechallenge of transparency. Thechallenge is merely trans-ferred to another level. Thetemplate against which theinstrument compares thegiven signature willundoubtedly comprisesensitive information. Thatinformation itself needs to beverified before the instrumentmay be used to authenticateincoming warheads, sinceotherwise there will besuspicion that the templatehas been made broad enoughto accept hoax warheads.The above will inevitablyinvolve the transfer of somesensitive information, and will

therefore require transparencyagreements. Leaving asidehow to achieve such trans-parency, one advantage to thisapproach is that suchagreements could be restrictedto the participating NW StatesParties. This leaves thepotential for theauthentication/verificationprocess to be carried out by atrusted third party, such as theIAEA, who would not beprivy to the data transmittedbetween the NW StatesParties to the transparencyagreement.

It is the absolute mode ofcomparison that shouldpotentially yield the highestlevel of confidence that theitem presented is a NW.However, given the realismassociated withmanufacturing tolerances, in-service warhead modificationsand the spread in a givenstockpile’s age, it will mostprobably require thecomparison to be made in astatistical sense. Thisprobabilistic approach, ratherthan a deterministic one,should allow States Parties torealise risk based criteria.Such an approach may helpminimise potentially frustrat-ing and disruptive false-alarmchallenge inspections.

The relative comparison ofmeasured and stored(template) data, eg highresolution gamma-ray spectra,can be undertaken to a muchhigher degree of precision,leading to improvedconfidence in theauthentication process. The

page 18

design and authenticity of thetemplate, the tolerance to be appliedin the comparison process and hencethe risk of ‘leakage’ of hoaxedwarheads then becomes the issue.

The design of computer-based dataacquisition and analysis systems,that have no clandestine datastorage or transmission capabilityand provide high confidence thatsensitive measurement data cannotbe compromised in the course ofverification, is not examined furtherin this paper. However, there ispractical evidence that suchperformance requirements can bemet. It is also considered that suchan approach does not impact thegeneral applicability of NDAtechniques, except for conventional(i.e. non-digital) radiography, whichdoes not rely upon computerarchitecture in order to generate apicture.

NDA techniques as applied to genericwarhead designs

The table in Appendix B illustratesthe information that can be obtainedby individual and combinedradiometric NDA techniques appliedto a likely NW. (Note, the word‘likely’ is used since not all serviceNWs follow similar designconcepts.) It should be noted thatthe level of detail associated withSNM and other radioactive and non-radioactive components increases indescending order in the table.Correspondingly the level ofconfidence in the item under assaybeing an authentic NW improves thefurther one moves through the table.The possible NDA techniquesdescribed in Appendix B are nowconsidered relative to a number ofgeneric NW designs in the followingparagraphs.

Plutonium-based single-stage NW

In general, for simple Pu basedsystems, the chemical form of the Puis known, for example metal.Quantification of the amount of240Pu present should be attainableusing passive neutron coincidencecounting provided the detectionefficiency is both known (andindependent of item buildconstruction) and uniform.Uniformity of neutron detectionefficiency is required to take accountof the likely variability in size ofsingle-stage Pu components. Ifneutron multiplicity counting isapplied the measurement of 240Pumass is simplified since there is norequirement to know the neutrondetection efficiency. Determinationof the total Pu mass requires HRGS-derived Pu isotopic data. In this casethe gamma-ray attenuation causedby materials outside the Pu (e.g.explosive, reflector materials andouter case) is assumed not topreclude such an isotopicassessment. Further studies,however, are required in this area.

If the chemical form of Pu remainsunknown (i.e. HRGS sheds nofurther light on compoundconstituents) then the 240Pu mass canonly be determined by neutronmultiplicity analysis. However,because the multiplicity technique isrequired to determine threeunknowns in such circumstances(i.e. 240Pu mass, neutronmultiplication and the ratio ofspontaneous fission to (α,n)generated neutrons), the neutrondetection efficiency must be assessed independent of the multiplicitymeasurement. Again, the detectionresponse should be uniform withinthe region occupied by the item

page 19

under assay and independentof the item build constructionfor it to be applicable to therange of NW types likely tocome under a global Treaty.Whether such neutrondetector responsecharacteristics can be met inpractice requires furtherstudy.

A detailed analysis of neutronmultiplicity and HRGS-derived data should not onlyprovide information on the Pumass but also on likely non-radioactive components suchas conventional highexplosives thickness, and theidentification of reflectorand/or tamper materials. Thefeasibility of determining theexplosive type from themagnitude of various emittedsecondary gamma-raysrequires further study.Although it is known to betechnically possible underwell controlled conditions, therobustness of this approach isdependent upon thesensitivity of secondarygamma-ray production ratesto the neutron energyspectrum, which is itselfdependent upon the geometryof the Pu component and thesurrounding inert materials.

Highly Enriched Uranium-basedsingle-stage NW

Work undertaken at AWEindicates that the only mannerin which an amount of bulk235U in an operationalwarhead assembly can bereasonably determined is byactive neutron interrogation.

For example, in an implosivedesign, conventional highexplosive completelysurrounds the enricheduranium. The high-energyincident neutron flux will, bythe time it reaches the 235U, besufficiently moderated (tothermal neutron energies) thatthe detected response will beproportional to the outersurface area of the enricheduranium rather than the bulkvolume (mass).

Whilst HRGS can be appliedto yield the enrichment ofbare or lightly shieldeduranium, this usually simplemeasurement can be thwartedby the presence of highexplosive or other NWshielding material.Alternatively, an outer NWcase composed of natural ordepleted uranium may bepresent which may or maynot completely mask thegamma-ray signatureemanating from the innerenriched uranium. In this casethe enrichment value of theuranium first stage will bebiased low, with the resultthat the total U mass isoverestimated. This over-estimation, could be bounded,however, by a surface areameasurement obtained usingactive neutron interrogation.Because of these difficulties inaccurately determining theenrichment it is consideredthat active interrogationshould be specifically tuned toquantify 235U amounts only.This requires the interrogatingneutron energy distribution tobe suitably tailored to

minimise the likelihood ofassociated 238U fission. Thefeasibility of achieving thedesired 235U measurementsensitivity in the likelypresence of an outer naturalor depleted uranium caserequires further assessment.

Composite Pu/enriched U-basedsingle-stage NW

The applicability of neutronmultiplicity counting (or anyother neutron NDAtechnique) to composite Pu/Ushells is possible in order torealise a measurement of theneutron multiplication andhence an accuratedetermination of the 240Pumass. If the measuredmultiplication is considered tobe too high for the totalamount of Pu present (i.e.assuming it was a Pu onlydevice), a lower limit on the235U amount could becalculated. The actual value of235U mass present, however,would be dependent uponknowledge of its associatedgeometry.

The likely shielding of Pu byan outer shell of enricheduranium will render the Puisotopic determinationdifficult. Quantification of theenriched uranium constituentmass (likely to be identifiedby HRGS) could be obtainedusing the spontaneous fissionneutrons from Pu as an activeinterrogation source, however,the interpretation of suchmeasurement data isconsidered difficult. Whilstdifferential absorptionanalysis of Pu gamma-rays

page 20

transmitted through an outerenriched uranium shell may lead toan estimate of the thickness ofuranium it is not possible to infer anactual uranium mass. The accuracyis dependent strongly on thenumber and type of other absorberspresent in the item. Unless there isgood design transparency, the shellradius will most probably not beknown.

If the ordering of SNM materialtypes within the composite werereversed, the same aforementionedchallenge associated with theinterpretation of neutronmeasurement data will exist.

Quantification of both Pu andenriched U components isconsidered a difficult task. If one ofthe acceptance criteria for theauthentication process was the totalamount of fissile material present,requiring knowledge of both Pu andenriched U components, then such aNW design poses a significantchallenge. It implies (as a result ofmeasurement inaccuracy) abroadening of the acceptable fissilemass range, and hence a lowering ofoverall confidence in any decisionrelated to NW authenticity.

Two-stage NW designs (with single orcomposite SNM first stage)

Although such designs are normallyassociated with larger amounts ofSNM, the interference of radiationsbetween and from the two-stagesmakes any quantification of SNMmasses extremely difficult. This isparticularly so in the case of gamma-ray based measurements for whichdetector collimation now becomesan important issue, in order toisolate direct passive gamma-ray

emanations from the first or secondstages. If the two stages becomeneutronically coupled (due, forexample, to close proximity and/orpresence of moderators enhancingthe thermal component of theneutron energy spectrum) then theitem will exhibit a single neutronmultiplication. This will again makeit difficult to provide an accuratedetermination of the spontaneouslyfissioning amount of Pu present inthe item.

Discussion

From experience it is considered thatradiometric NDA measurementsconducted only on a simple metalPu-based single-stage NW canprofitably yield absolute informationon:

4 the quantity of Pu within the item and its neutron multiplication, and

4 other non-RA components (material types and, in somecircumstances, associatedthicknesses).

For all other warhead assembliesconsidered, the uncertaintiesassociated with absolutedeterminations of SNM mass arepredicted to be large with lowprobability of reliable informationregarding non-radioactivecomponents. Bulk 235U massdetermination by active neutroninterrogation is difficult withoutaccess to empirical, warhead-specificresponse data.

It is therefore not consideredpossible, within a global Treatycontext, with many warheadconfigurations and incomplete

page 21

design transparency, toauthenticate with completeconfidence an item as being astockpile nuclear warhead (ornot) by non-destructiveradiometric assessment alone.Radiometric studies of an itemcan, however, provide somedata, particularly related tothe fissile materialconfiguration. However, thenumber of such operationalconfigurations that could beused in a viable nuclearwarhead design is large andthere is (currently) notsufficient transparencyregarding warhead designsbetween the Nuclear WeaponStates. Under suchcircumstances authenticationconfidence, based on NDAalone, rapidly diminishes. It istherefore important thatpotential warhead designclasses applicable to a Treatybe understood for theirimpact on verificationconfidence.

“It is not consideredpossible.... toauthenticate with

complete confidencean item as being astockpile NW (or not)by non-destructiveradiometricassessment alone”

Data protection requirementsarising from the need toprotect sensitive informationrelating to a warhead’sconstruction do not appear topresent technical obstacles indeveloping and implementinga radiometric measurementstrategy to aid NWauthentication as part of adata fusion process.

A NW authentication scenariohas been investigated whichonly uses radiometric NDAtechniques and assumes littleor no design datatransparency (but where fullaccess to the device is grantedfor the respective measure-ments). It does not appear tobe a practical propositionsince it would require theimplementation of

unreasonably large tolerancebands, which will quicklydiminish confidence in theauthentication process.

Work during the study phasehas considered the use of bothactive and passive radiometrictechniques for warheadauthentication. We recognisethat other (non-radiometric)techniques are available, andthese will be investigated inmore detail in the researchphase.

In conclusion, we considerthat NW authentication mustinclude, in a data fusionsense, radiometric, non-radiometric and provenanceinformation from variousverification techniques andprocesses. We believe byadopting such an approach,States Parties to a globalTreaty will have the bestchance of achieving theobjective of verifiable nuclearwarheads authenticationwithin acceptable level ofconfidence.

� In this paper the term non-destructive assay is used to embrace those techniques biasedtowards assaying material in a warhead. Non-destructive evaluation, however, is also used todescribe those tecniques that are biased towards characterising a warhead’s signature in abroader sense, for instance its infra red signature.

� The need for a provenance principle follows from the assumption that a NW signaturewill never be absolutely identifiable, but will inevitably be assessed, against a level ofconfidence, as being consistent with a given NW class or unit type. If, however, the NWsignature data is melded with an established point of provenance (that is the NW’s chain ofcustody maybe sourced to a credible stockpile point of origin) then this will increaseverification confidence.

� The terms SNM and fissile material are used in an interchangeable sense in this paper.

� The study phase, by design, has focused on radiometric and radiochemical basedtechniques, where AWE has considerable warhead related experience. It is recognised,however, that a robust verification regime will be realised best by applying a broad spectrumof many verification technologies, covering many data sources and types.

page 22

Dismantlement and Disposition

Introduction

The purpose of this chapter is todiscuss some of the issues that mayarise following the withdrawal of anuclear warhead from a stockpileand its entry into a dismantlementand disposition chain. It is assumedthat the NW has been authenticatedand its provenance established.

From a purely technical viewpoint,and to illustrate some of thethinking, the following conditionsare considered to represent thepractical stages of dismantlement fora single stage NW:

i. Nuclear physics package and other NW component sub-assemblies separated from the delivery vehicle.

ii. As i with additional evidence that the high explosive and fissilematerial components have been physically separated from each other.

iii. As ii with additional evidence that the fissile material component has been de-militarised to such an extent that complete reworking would be required for it to be reused as a warhead component. This could be as a result of irreversible disablement, such as ‘pit stuffing’, or a process where the nuclear material is stored under appropriate Treaty control or transferred to international Safeguards for storage or reactorburn-up.

The above represents variousdegrees of a postulateddismantlement process involving thefirst (and in many instances the

only) stage of a NW. Confidence inthe dismantlement processobviously increases as one descendsthe list until at (iii) it is consideredthat the fissile material associatedwith a functioning NW has been, toall intents, removed from thenuclear weapon process chain. Somehave suggested that a nuclearwarhead be considered to be‘dismantled’ when the highexplosive is removed from itsassociated SNM. However, bearingin mind that high explosive isreadily available and could be easilyreplaced to re-instate the NW, this isnot considered to be a meaningfulend state for a robust Treaty.

Treaty context

The number and types ofmeasurements needed to maintainconfidence during thedismantlement depends on thelevels of transparency beingoperated by the participating StatesParties. The former is inverselyrelated to the latter. These levels aresummarised below.

Free access to all NW components. Inthe limit unfettered inspector accessduring the dismantlement processmight be permitted. The mainauthentication measurementsneeded could confirm that the fissilematerial was part of a recognisedclass of design (mass, shape andisotopics etc). However, designproliferation sensitivity and nationalsecurity concerns means that thisscenario is considered most unlikely.

Some parts of dismantlement are opento observation, others are screened.Sensitive parts would be placed incontainers or screened through amanaged access protocol. The

page 23

number of techniques nowneeded to verify that thescreened components areindeed viable warhead partsis considerably increased,although the inspectors maybe confident of theprovenance of thecomponents as a result ofprevious nuclear weaponsarms control andauthentication processes.

Given that we conclude that itis difficult for NDAtechniques alone to provideabsolute authentication thatan item presented is a NW,their role could become one ofproviding confidence that anitem can be tracked throughdismantlement. That is fromits entry into an armsreduction process, and being‘baselined’, through to finaldisposition. On exit fromdismantlement, anyverification process mustprovide evidence that theSNM is no longer part of aNW. Such a role is, however,contingent on the provenanceof an item as a stockpile NWhaving been previouslyestablished.

Item tracking may beachieved through directintervention, say bycomparison of passivelyemitted or induced radiationsignatures, or through moreadministrative arrangements,such as tagging. The extent towhich the SNM must beseparated from the NW, so asto be no longer considered aviable NW, is open to debate.Treaty considerations may

lead to the likelihood that thedisassembled componentscan, within a defined timeinterval, be reassembled, thusallowing the realisation of aso-called virtual deterrent.Whilst such issues may formpart of the current debate,they are not consideredfurther in this paper, exceptby noting that such ideascould influence the confidencelevel associated withconfirming the finaldisposition of a NW.

As a two-stage NW cannotoperate without a functioningfirst-stage (primary) then, atfirst glance, there may be atendency to assume thatevidence that all SNM andother radioactive materialspresent in the second-stage(secondary) have beenremoved is not required.There may also be a view thatonce the warhead case, of atwo-stage NW design, hasbeen removed, it should bepossible to adopt a morerelaxed approach todemonstrating that thesecond-stage per se has beendismantled. Suchassumptions, however, aredangerous, as it may still bepossible to utilise a separatedprimary (in a newconfiguration) and that thepossibility of diverting andreworking the secondaryfissile material to a primaryrole is certainly a threat.Control and accountability ofall fissile material in a NWshould be seen as the mostrobust approach.

Observation of dismantlementby second or third partyinspectors is forbidden. Asabove it is assumed that theincoming warhead’s signaturehas been previouslyauthenticated and itsprovenance confirmed by arobust chain of custody,operating within an armscontrol/accountancy regime.As sensitive parts arecontainerised, the number ofverification technologies thatcan be employed for thediagnosis of the criticalcomponents is very likely tobe restricted. This approachprotects State-sensitiveinformation and if only forthis reason it is considered aplausible model for averification regime. [Theissues and complexity ofwhether to place emphasis onthe materiel entering a facilityor the materiel leaving it,needs to be understood,especially if the facility isoperationally maintaining a

legitimate stockpile.]

Preserving confidence in anyarms reduction verificationregime requires credible chainof custody to be maintained. Ifdirect inspection of a processis not allowed, it remains toensure that opportunities forillicit diversion of material orcomponents are minimised.The challenge is compoundedby the fact that the compo-nents most needing efficientaccounting procedures cannotbe directly inspected.

page 24

“Preserving confidence inany arms reductionverification regimerequires a credible chainof custody”

The challenge, however, is notentirely unique to the nuclearweapons industry. For example, inmany cases the accountable materialcontained in fuel rods is alsoinaccessible for direct inspection.Regimes that rely on itemaccounting and material balanceareas have been regularly andsuccessfully used by agencies suchas the IAEA and EURATOM toaccount for nuclear material used inthe civil programme.

There is no reason why such systemscould not also be successfullyadopted in the nuclear weaponscommunity. The same techniques foritem tracking previously discussedmay also be used on entry to andexit from any dismantlement facility.Tracking and security interventions,such as portal monitoring of vehiclesand personnel, remote surveillanceusing closed-circuit TV cameras andradiation detectors, physicalsegregation of the facility andbetween-process sweeps forundeclared material, will need to beappropriately chosen for the NWregime.

There is one difference, however,that poses an extra challenge. Themass and isotopic make-up of fissilematerial used in fuel rods, unlikethat used in a warhead, is not asensitive value. In the absence ofsuitable transparency agreementsthis would create difficulties whenattempting to account for the fissile

material resulting from a NWstockpile. If the mass of fissilematerial in warhead components isunknown, that would not allow adirect connection between thenumbers of such componentswithdrawn from the stockpile andthe amount of fissile materialentering Safeguards. Two mitigatingfactors are recognised, whosesensitivity requires furtherinvestigation during the researchphase:

i. If the warheads being removed from service are of relativelyconservative design, then release of the corresponding design information may not be considered a proliferation risk (Use of this option wouldprejudice the next factor if thefissile material from both were being combined); and

ii. the fissile material could be mixed with that from other warhead types, so that it would only be possible to ascribe an average value for the warheadfissile masses and isotopiccomposition.

Signature measurements andcomparisons for verifyingthe dismantlement process

It is considered that NDAmeasurements should be able toconfirm, to some specified level ofconfidence:

i. that the item contains SNM and, dependent upon SNM type, the identity of other non-radioactive (inert) constituent parts, through (n,γ) interactions in which the source of neutrons may

page 25

arise from spontaneous fission decay or induced fission driven by an external neutron source;

ii. that the facility within which the SNMcomponents are processed remains within accepted process operating bands, thereby ensuring highconfidence tracking;

iii. that the radiationsignature(s) from the SNM remain unchanged since the last NDA measurement,taking into account any natural radioactive decay; and

iv. that, as a result of the dismantlement process, there is high confidence that the primary’s SNM has been removed, and the location of the SNM after removal isknown.

It has been assumed, for thepurpose of developing thescope of further studies, thatwhilst a NW may beappropriately packaged foroperational storage andtransport, there will be aminimum overpack orcontainerised state appliedduring dismantlement andintra-facility moves. For thepurpose of conducting NDAmeasurements as the NWmoves through adismantlement facility (orfacilities), this may require theremoval of the NW from itsintra-facility container and,via a managed access process,presentation for verification in

order to minimise theshielding of radiationsignatures. The followingsection discusses some of theNDA techniques that mayhave utility duringdismantlement.

Baseline signaturerequirements

Gamma-ray spectrometry

As with authentication, thisshould be the high resolutiontype of gamma-rayspectrometry in order to makebest use of spectral detail fromthe NW and should beundertaken in a mannerwhich views the completeextent of the NW and itsassociated overpack orcontainer. If collimation of theHigh Purity Ge (HPGe)detector is required, then thecounting geometry must besuitably adjusted to ensurethat the complete overpack ismaintained within thedetector field of view. Thiswill effectively isolate the NWgamma-ray signature frominterference effects caused, forexample, by the proximity ofother collocated NWs. In thefinal analysis it may benecessary to separate a NWunder inspection from othersin the store in order tominimise such interference.The resulting gamma-rayspectrum will be a complexfunction of the NW deviceconstruction (exhibiting theeffects of componentshielding, SNM self-shieldingand (n,γ) interactions) and

device-detector countinggeometry. Falsification of thisspectral detail, following theinitial baseline measurement,is considered to be virtuallyimpossible to achieve. The(n,γ) spectral component willbe extremely sensitive to anyattempt to remove orsubstitute SNM, an activitythat may go undetected ifreliance is based uponmonitoring of only the passivegamma-rays emanating fromthe SNM itself.

Neutron NDA measurements

For a Pu based NW, sinceneutrons are significantly lessaffected than gamma-rays byshielding materials presentwithin the NW body, it ispossible to employ passiveneutron detection to providefurther verification confidencein NW tracking anddismantlement processes. Thisfollows from the fact thatneutrons are not subject to thesame degree of self-attenuation and theassumption that there is asufficiently large source ofSNM spontaneous fissionneutrons available. If the SNMwithin the NW does notcontain a significantspontaneous fission source,for example in an HEU basedNW, then active neutroninterrogation must beundertaken. In both cases,spontaneous and inducedfission neutrons will alsoproduce secondary gamma-rays associated with thepresence of inert components.

page 26

“If the SNM within theNW does not contain asignificant spontaneousfission source.. then activeneutron interrogationmust be undertaken”

The magnitude of the detectedneutron signature is, as previouslyindicated, a complex function ofmany parameters. For example, theSNM mass, chemical andgeometrical form, isotopic make-upor degree of enrichment, and theextent to which the SNM mass isneutronically coupled to other (mostlikely inert) moderating or reflectingmaterials consistent with therequirements for a viable NWdesign. Given that such a grosssignature is a function of so manyinteracting parameters it isconsidered extremely unlikely, onceauthentication and baselining hastaken place, that covert SNMsubstitution can take place withoutdetection.

Whilst the complete or partialsubstitution of SNM by a simpleneutron-emitting radioactive sourcemay present a total neutron outputcommensurate with that of theoriginal SNM mass, it is consideredthat the following are possibletechniques that could be exploited inorder to detect SNM substitution.The sensitivity of these individualsignatures to neutron source typeneeds further study. This willestablish those neutron signaturemeasurements that will providemaximum confidence in NWtracking and dismantlementverification:

i. relative differences in source neutron output energy spectra and/or any induced (n,γ) gamma-ray signature;

ii. simple repeat measurements of total neutron output over apre-determined time interval; and

iii. the use of neutron multiplicity counting techniques to examine multiplicity of detected neutrons

When active neutron interrogation isapplied to an HEU design, themagnitude of neutron output fromthe NW is dependent upon theenergies of the interrogatingneutrons causing fission and issensitive to the overall measurementgeometry. This particular inducedneutron signature, as well as itsassociated (n,γ) output, does notlend itself to easy falsification (solong as the interrogating neutronenergy is kept below the thresholdlevel for fertile 238U). A detailedunderstanding of the impact ofmeasurement geometry upon theinterrogating neutron energyspectrum, however, is required toestablish the practical viability ofusing this signature.

Given that shielding of extraneousbackground neutrons is difficult toachieve (and is certainly moreproblematical compared to theprovision of gamma-ray shielding),careful consideration will have to begiven to the design of detectordeployed and the measurementgeometry adopted for the purpose ofmaking neutron measurements. Thisis particularly true if the detectionhead is integrated within an activeinterrogation system. Whilst simpletransportable, and in some instances

page 27

even hand-portable, neutronpanels can be used for grossneutron counting, theygenerally possess insufficientdetection efficiency to makestatistically meaningfulmeasurements of neutroncoincidence (i.e. pair ortriples) detection rates.Moreover, such measurementsare susceptible to backgroundeffects associated with thelikely proximity of other NWsor fissile material if they arerestricted to simple totalsneutron counting. If, however,a design of neutron detectorcan be deployed that fullysurrounds the NW understudy, then its ability to makeneutron multiplicitymeasurements is greatlyenhanced because of theimprovement in detectionefficiency. Under suchcircumstances the influence ofnearby NWs upon themeasured coincidence andtriples rates is significantlyreduced.

Environment Monitoring

The possibility of collectingand measuring the gasesemitted from thedismantlement process, toverify that certain warheadmaterials are present, mayalso have utility. Organicmaterials and explosiveseffluents may provideverification information.Plutonium and uraniumparticulates may also becollected from stack filters.In order to understand thevalue of such environmentalmonitoring data, it is intended

to use AWE’s currentChevaline disassemblyprogramme as a means ofgathering forensic informationon a particular warheadsystem’s disassemblysignature.

Subsequent work willcompare the Chevalinewarhead system with thesignature from other AWEoperations, thus providing animportant, albeit limited,insight into facility specificsystem statistics and system tosystem variations.

Confidence indismantlementverification

Earlier in this chapter, threepossible states ofdismantlement werepresented, that would rendera simple single stage NWinoperable. For each of thesestates Appendix C presentsthe various radiationsignature measurements andtheir combinations that wouldassist in verifying each stateand provides a qualitativemeasure of the confidencelevel likely to be achieved.The stated signature approachimplicitly assumes that a base-line measurement exists,which will be used as part ofthe tracking process throughto the eventual dismantlementfacility.

As was discussed in theprevious chapter, NWauthentication is challenging

if NDA is used alone. It isconsidered, however, thatneutron, gamma-ray andenvironmental monitoring-based NDA technologies canall be applied to NW trackingthrough dismantlementprocesses such that highverification confidence may beachieved. At the heart of theradiometric NDAmeasurement is therecognition that:

i. the coupling of radioactive and inert components of a NW through the (n,γ)interaction yields a gamma-ray signature that is an extremely strongfunction of the NW design and build, providing a robust baseline signature for future comparison purposes.

ii. following from (i), the strong neutron energy dependency of (n,γ) gamma-ray yields (with neutrons arising either from passive spontaneous fission or from the fission-inducing interrogating flux combined with theresulting induced fissionneutrons) makes it difficult to see how this gammasignature can itself be mimicked by other types of substitute neutron emitting, non-SNM, source.

iii. neutron and gamma-ray techniques complement each other to the extent that attempts at material substitution prior todismantlement (involving

page 28

changes in mass, material type, isotopic form,enrichment, SNMgeometry) are considered detectable even incircumstances whereradiation self-shielding effects could provide scope for covert materialsubstitution. To this end neutron and gamma-raymeasurements must be conducted simultaneously, or at least in circumstances where there is noopportunity for the NW under study to betampered with between measurements.

iv. there are sufficientsignatures available prior to and followingdismantlement to confirm that either the original NW has been altered incomponent configuration or, through the directmonitoring of the removed component(s), that the SNM is the same material as that which entered the dismantlement facility,predominantly through confirming isotopic form/enrichment and, for some SNM types, its age.

It is recognised that the above will bestrongly influenced by the level oftransparency in operation. Furthertechnical studies have been identifiedwhich will investigate the worth ofnuclear-based NDA, non-nuclear basedNDA and other measurementstrategies, intended to provide highconfidence in NW tracking and theverification of NW dismantlement.These studies will also investigate

techniques and processes for themaintenance of a chain of custody.For instance, the value of proven‘tagging and sealing’ technologiesfrom other verification regimes, suchas IAEA/EURATOM Safeguardsand Chemical Weapon Convention,will be evaluated for their nuclearweapons arms control use.

Dismantlement facilitysurveillance

The combination of radiometric,non-radiometric and environmentalsignature measurements performedon both the SNM componentsremoved from a NW and theremaining NW body is considered tobe the most effective approach toverifying dismantlement.Maintaining surveillance (trackingand tagging) of these discrete itemsshould increase the overallconfidence. That is maintaining anappropriate ‘chain of custody’.

The surveillance process itself willalso benefit from only a single typeof SNM-bearing item beingpermitted within a dismantlementfacility. That is the NW beingpresented for reduction. If thedismantlement facility is part of alarger facility it will be necessary toensure that effective controls are inplace to prevent clandestine orpotentially conflicted operationalmovement of other SNM into or outof the facility.

Approaches to radiation-basedsurveillance are discussed below, aswell as the application of existingradiation sensors to monitor entryand exit points. As has beenpreviously noted, addressing theissues of a nuclear weapons arms

page 29

control (accountancy) regimeat the integrated level willfocus debate in this area.

It is considered thatsurveillance of dismantlementfacilities could be met by theuse of:

i. fixed gamma, neutron and environmental monitors strategically placed around the facility so that one or more detectors cover every area that the SNM component and remaining NW body can move within,and

ii. a combined mobile gamma/neutron detector collecting signaturemeasurements whilst simultaneously recording the location of the monitor as it is moved through the facility (again covering all those areas in which the SNM component and NW body can move).

An analysis of the monitordata collected by either meanscan yield a near real-timepicture of the movement of alldetectable NW componentsthrough the dismantlementplant. The confidence levelassigned to the sourcelocation(s) can be improvedby weighting the monitor datato reflect the average radiationattenuation factor anddistance covered by eachindividual monitoringlocation. Whilst thesurveillance monitors will bedesigned for optimum

detection efficiency (mostlikely at the sacrifice of energydiscrimination which is notrequired for this activity),efforts should also be made toensure that SNM intra-facilitytransport containers allow themaximum transmission ofradiation to ensure successfulsurveillance tracking.

The overall performance of anear real-time radiation-basedsurveillance system isconsidered to depend largelyupon system hardwarereliability, the selecteddetector head efficiency andthe robustness of thealgorithms used to determinesource location(s). The spatialresolution capability of thesystem will depend upon thenumber of monitoring headsdeployed. There are a numberof such surveillance systemscurrently in use and the futureprogramme will ensure thatthe appropriate knowledgeand experiences that exist arecaptured and applied to thenuclear weapons arms controlresearch work.

Part of a nuclear weaponcontrol regime, for ensuringthat no SNM, other than thatin a NW due for disposition,is delivered to thedismantlement facility and de-conflicted from other Treatypermitted work, is the use ofportal radiation monitors,through which vehicles andpedestrians must pass to gainaccess. In addition,vehicle/body searches prior toentry and on exit may need to

be conducted using portablehand-held monitors capable ofrapid SNM detection.

Such monitors cannotguarantee the detection of allSNM [detection limits for barePu range from < 1 g (~ 10s gfor bare 235U ) to ~ 10 g (~100s g - 1000 g 235U)dependent upon monitortype]. Detection is also highlysensitive to item shielding.However, monitors normallyform one element of anoverall SNM protection andphysical control regime thatcan also include the use ofCCTV, time-lapsephotography, movement-sensors, tamper-indicatingdevices and seals etc.IAEA/EURATOM Safeguardshave over many years,established and implementedsuch regimes to control andguard SNM within the civilnuclear fuel cycle. Equivalentprocesses may be suitable forimplementation as part of NWcontrol and reduction process,possibly extending to othernon-radioactive, but stillsensitive, NW components.

Disablement anddemilitarisation

The use of disablementtechniques to deny the use ofnuclear warhead componentswithout significant, andtherefore detectable rework, isnot strictly a necessaryrequirement of an armsreduction regime. It does,however, increase confidence

page 30

that warheads declared surplus torequirements may not, perhaps dueto a worsening political situation,subsequently be reallocated to thestockpile. This is particularlyapposite given the long lead-timesfor safe dismantlement of warheads.

The UK has operational experienceof disablement technologies, as earlyUK designs employed mechanicalsafing systems, that may have utilityin a nuclear weapons arms controlrole. Most of the techniques andcapabilities considered in the earlywarhead programme have notmatured to any great extent over theintervening period. They can beused as a realistic starting point for afurther consideration of the issuesrelevant to nuclear warheaddisablement, as part of nuclearweapons arms control dispositionprocess.

The techniques for disablement maybe broadly divided into two types:those that stop explosive assemblyof a warhead’s primary, or ‘pitstuffing’; and those that spoil a pit’ssymmetry. Both aim to change thewarhead characteristics so that thefirst (and perhaps only) stage of thewarhead cannot be operationallyused. It is thus taken out of thedirect warhead (reuse) cycle.

Disposition

Disposition is the disposal of fissilematerials from dismantled nuclearwarheads and its objective is tomake the reductions in nuclearwarhead numbers as irreversible aspossible. There are two recognisedroutes: by storing in a suitable stateor burning it in a suitable reactor.

Either way, the important feature isthat the materials end up in a formfrom which the return to warheaduseable status would be costly andtime consuming, and, mostimportantly, transparent toverification.

The first step in any dispositionroute is to reduce the fissilematerials into a warhead insensitiveform, which may include isotopic‘denaturing’. The second would beto place the fissile material underappropriate control, for exampleInternational Safeguards.

Non-fissile components, for instanceorganics, explosives and electronics,also arise from the dismantlement.Whilst the prime focus shouldremain with fissile materialdisposition, there is merit inensuring that critical NWcomponents are also irreversiblydisposed of, particularly thosewhose manufacture does not resultin a strong environmental signature.

Disposition of an entire stockpile orclass of warhead system may takedecades to complete. It is likely thatthe Nuclear Weapon States will havestocks of warhead grade Pu andHEU on their hands for a long timeto come and so the threat ofpotential breakout will exist longinto the future. It is recognised thatmuch debate and work has takenplace on this subject in other Treatyregimes and it will be importantfrom a verification perspective forthe research programme tounderstand any previousdemilitarisation and dispositionexperience.

page 31

Nuclear weaponinfrastructure controland dismantlement

The principal thrust of thispaper has focused on thechallenge of authentication ofa warhead and its main sub-assemblies, dismantlementand disposition. However, ifglobal nuclear weapons armscontrol is to be realised, theimpact of evasion andproliferation minimised (bothvertical and horizontal), thenit will also be necessary toaddress the control of keyindustrial facilities andprocesses within the nuclearweapon complex. This aspectof the work has an obviouslink to export and non-proliferation controls.

Nuclear weapon facilitydismantlement verification isa relatively immaturecomponent of the globalnuclear weapons arms controland non-proliferation scene.Although the UNSCOM workhas highlighted one approach,namely that of facilitydestruction within a challengeinspection regime, this wasaccomplished within arelatively crude industrialcomplex. However, within amultilateral or internationalTreaty, infrastructure(facilities, processes andmateriel) verification will bemore complex. A balance willneed to be struck betweenverifiably reducing a StateParty’s nuclear weaponindustrial infrastructure,whilst at the same time

allowing Treaty-permittedstockpile production andrefurbishment. All withoutcompromising nationalsecurity.

Studies are planned toimprove our understanding ofthese issues and AWE’sexperience, as well as otherUK groups and agenciesassociated with nuclearfacility decommissioning, willbe brought to focus. Forexample, the practicalities andpotential Treaty issuesassociated with verifiablymaintaining, reducing ordismantling a nuclearwarhead productioninfrastructure, as well as whatconstitutes a minimumwarhead-infrastructure?

Discussion

Gamma-ray and neutronsignatures from SNM can becombined to yield very highconfidence in NW trackingand dismantlementverification. This requires theverification inspection processto start from an authenticatedpoint (of high confidence andappropriate provenance) atwhich items presented forNDA inspection are bona fideNWs. The proposed NDAmeasurement regimeexamines the coupling of bothradioactive and inertcomponents through the (n,γ)interaction, which yields agamma-ray signature that isan extremely strong functionof the NW construction,providing a robust signaturefor future comparisons. This

signature, together withinformation from themeasured neutron output(passive or induced), isconsidered to be unique to theNW type and, once baselined,cannot be mimicked orsynthesised by other means,including the substitution ofSNM with other radioactivematerials.

Radiation monitoring atentry/exit points to, and in-situ surveillance monitoringwithin, a dismantlementfacility can also aid NWdismantlement confidence,but only as a supplement tothe detailed signaturemeasurements made on theNW itself (including removedSNM component and theremaining NW body). Suchmonitoring and surveillancesystems already exist underIAEA/EURATOM Safeguardsand are fully integrated intooverall material control andprotection regimes. Their rolein a NW regime will beevaluated in the researchphase.

The use of (comparative)NDA techniques during thedisassembly and dispositionprocesses present a less stress-ful task than that associatedwith NW authentication.Nevertheless, work will berequired in order that theoperational and forensicenvelopes of the varioustechniques (radiometric andnon-radiometric) may beunderstood in a verificationcontext.

page 32

Introduction

The previous sections of this paperhave focused on the ‘foreground’issues associated with verifiablyauthenticating, dismantling anddisposing of declared warheads. Thepurpose of this chapter is to discussexisting and emerging ‘background’technologies, skills and techniquesthat can be used to establish theexistence and/or the status of anuclear weapon complex (itsinfrastructure capability) and itsprogramme (operations). Some ofthe techniques and processes alsohave a potential role duringwarhead authentication and duringchain of custody tracking.

We consider nuclear weaponinfrastructure control to be anecessary aspect of any verificationregime directed towards confidentlyachieving low levels in globalnuclear warhead stockpiles anddemonstrating the compliance ofany State Party to a Treaty.

The objectives of verification includeboth ensuring that warheads aredismantled and that no furtherwarheads are added to the stockpilebeyond any agreed level. Forplanned monitoring of nationalweapons plants, transparency isessential. Thus, as with authentica-tion, any measurements taken mustprovide Treaty complianceverification information without dis-closing sensitive warhead design ornational security information thatmay contribute to proliferation.

Environmental monitoring (EM)should be seen as a backgroundprocess to the more potentiallyintrusive warhead authenticationand dismantlement verificationprocesses. Environmentalmonitoring is directed at providingsupporting confidence that a StateParty is not involved with warheadproduction outside of any Treatyagreement.

During the study, we haveinvestigated the measurements andrelated techniques that we believehave relevance to verifying a StateParty’s nuclear warhead productioncycle within a Treaty. For example:

4 the total nuclear warhead cycle and definition of species likely to be emitted at each stage, with their possible location andchemical forms;

4 possible techniques for sample collection on-site and far-field;

4 possible techniques for real time in-field monitoring on-site and far-field;

4 possible laboratory analytical techniques, both chemical and physical, to be used on thecollected samples;

4 the management andinterpretation of theintegrated information gathered from all sources.

Monitoring the Nuclear WeaponComplex

page 33

Environmentalmonitoring overview

Environmental monitoringcan assist a nuclear weaponsarms control verificationprogramme in four ways.Which aspect is mostimportant at any one time is afunction of the politicalsituation and the level of co-operation given by a StateParty being inspected:

4 provision of continuous (background) monitoring around sites to detect changes in effluentsrelevant to materials in the nuclear warhead’s life cycle;

4 as part of on-siteinspections, including monitoring for evidence of production, assembly,dismantlement, disposal or storage;

4 area monitoring to locate covert plants involved in the nuclear warhead’s cycle;

4 provision of supplementarydata as part of theverification process fordismantlement of nuclear warheads.

Continuous monitoring byenvironmentalcollection/analysis andassessment at each stage ofthe nuclear warhead’s cycle is

considered an importantaspect of being able tomaintain confidence in anuclear weapons arms controlverification regime. Remotemonitoring increases confi-dence in the arms reductionprocess since it provides infor-mation about facility opera-tion in the absence ofinspectors. EM also has thedesirable effect of reducingthe inspectors’ received radia-tion dose. Changes in theenvironmental signature at asite can be linked back tochanges in the workload andworkflow. Monitoring for thevarious materials in thewarhead and their environ-mental signatures is vital inverifying the presence offissile and critical materialsused for nuclear warheads.Quantification of thesemeasurements can be usefulin accounting for warheadmaterials.

“Monitoring of thevarious materials inthe warhead andtheir environmentalsignatures is vital inverifying the pres-ence of fissile andcritical materials usedfor nuclear weapons”

The maturest EM model isthat exemplified by the IAEASafeguards programme,which has had the

responsibility forinternationally and regionallyaccounting and controllingfissile materials. The IAEAprogramme has recently beenextended, following the GulfWar where the production ofnuclear warhead materialswas being accomplished with-out IAEA knowledge. TheIAEA introduced the 93+2programme (which includesenvironmental measurementtechnologies) to enhance cost-effectively their capability todetect covert plants andoperations. The UK hascontributed to thisprogramme by, for example,contracting to use its owntechnical capabilities todetermine the presence andidentify the signatures offissile materials. This hasdemonstrated yet again thevalue of these technologies aspart of a verification process.

Environmental monitoringcan be used to identifymaterials relevant to thenuclear weapons programmeat each stage of the nuclearwarhead production cycle,from ‘raw material’production through,potentially, to warheadassembly/disassembly.Identifying materials and localbackgrounds for a particularprocess and plant (baselining)provides importantinformation for verification.The EM process must includea well-established databasethat contains sufficient detailto enable interpretation of the

page 34

operations and be operated bytrained personnel who can monitorthe processes with time.

It is necessary to understand whatenvironmental monitoringtechnologies effectively cover whichparts of the full verificationspectrum. In addition to theenduring techniques, emergingtechnologies (some of them usingnew techniques and others makingportable existing technologies) aredesigned to measure materials’properties, to identify a particularelement, signature and quantity, andrelate this to the warheadproduction cycle. Quantifyingbackground levels of these materialsfrom nature or other (legitimate)industrial processes will be essentialfor an assessment of any EMtechnique’s usefulness forverification. Too high or variable abackground makes interpretationdifficult and reduces the value of thedata.

The sampling of key materials willdepend on the routes by whicheffluents are emitted. In general,sampling will be either inside theplant, during on-site inspection(OSI) or close enough to a plant tominimise the dilution effects and tolink the material collected to theparticular plant. Care will berequired, as the possible signaturesfrom some materials could givedesign or warhead technologyinformation that may contribute toproliferation. The environmentaleffluents that are usually consideredare:

4 Gases and vapours collected from the plant (during OSI) or nearby;

4 Water from the waste streams and nearby lakes and streams. Vegetation close to the plant. OSI inspections could involve collecting liquid samples and vegetation from the site;

4 Particulates from plant stack samplers or in plant and outside verification monitor filtersamplers.

Environmental monitoringapplication

Facility monitoring

For verification purposes, facilitieswould be monitored to ensure thatno clandestine material enters awarhead production cycle. If thisaspect could be tied down then onewould be seeking to verify thedestruction of warheads withouthaving to continuously be lookingfor new ones entering theproduction cycle.

Although not a prerequisite, weconsider the value of understandingthe size of States Parties’ stockpilesto be an important pre-cursor to anyTreaty. This knowledge becomesmore important the closer one getsto very low levels of warheadnumbers. The sensitivity ofaddressing nuclear weapons armscontrol on an absolute or relativebasis will inevitably be part of anynegotiation process. We thereforeintend to undertake a study on theissues associated with estimating aState Party’s stockpile. For example,we intend to make use of availabletools within the UK to understandthe verification of declarations that

page 35

may be made about a nuclearweapon complex’s processcapability. Contact will bemade with other UK centresto complement AWE’sexperience.

Environmental effluentmonitoring technologies arehighly relevant to monitoring.Field collection techniques arerequired for technologies forultra-sensitive measurementsand are likely to requirelaboratory based techniquesboth for increased sensitivity(as the samples are likely to be“far field” rather than closein). Samples need to besecurely handled to ensure theforensic integrity of samplesand results.

Also environmentalmonitoring technologies arepotentially open to cheating,by laying down a trail ofimitation materials, increasinglocal backgrounds to decreasethe sensitivity of the methods,or in some way disguising theemissions from the plant.

Transparency

It is highly unlikely that aState Party will allow the‘leakage’ or proliferation ofsensitive design informationduring any facility monitoringoperation. As with theauthentication process,procedures for takingsamples, transporting them tolaboratories and their analysismust be transparent andauditable.

Baselining

In a multilateral Treaty it willbe desirable for a State Partyto provide production recordsof warhead grade fissilematerial. The civil programshould be under InternationalSafeguards. Remote andvoluntary monitoringtechniques should give a levelof confidence in anydeclarations.

Any particular facility beinginspected or routinelymonitored should haverecords of any monitoring oftheir plant for safety or otherreasons and the amounts ofmaterial stored. It isrecognised, however, that notall facilities will follow similarstandards. Nevertheless,record data will form thebaseline or background for agiven facility. Independentestimates of the emissionsfrom the operations willprovide an adjunct and checkto any records-basedbaselining. It is from this

fusion of data, that futureeffluent measurements will becompared.Part of the proposed futurework programme will focuson the UK nuclear weaponscomplex, in order to evaluatethe accuracy of potentialdeclarations with regard toknown weapons useablefissile material output.

Data Collection, Storage andInterpretation

The intelligent use of allcollected data is necessary inorder to cover the entireverification spectrum. Thevalue of data fusiontechniques has beendemonstrated in other treatyenvironments and weconsider these to be anecessary part of a nuclearweapons arms control andreduction Treaty. Data fusionrequires the capability to storeand retrieve data, model andmap the information, bothhistorically and in real time, inorder to draw conclusions and

Individual Data Data FusionCoherent Verification

Information

page 36

help make decisions. Not all tech-niques will be applicable across theentire verification spectrum. It willthus be necessary to understand the‘limitations’ of each potentialverification tool in isolation and aspart of a data fusion process.Transparency issues will need to beaddressed, as the data, and the waythey are used, will determine theeffectiveness of any verification. Alltechnologies will need to be assessedand linked to provide a holisticpicture of the process being studied.Initially, all environmental effluentinformation will ideally need to bemapped to determine the status andbaseline of a particular plant orprocess. This will link into the othertechnologies, to provide confidencein any nuclear warhead reductions.

As the warheads are dismantled andmajor sub-assemblies and materialsplaced into store, information willneed to be continuously gatheredand checked for Treaty compliance.This leads to the conclusion thatverification is strongly coupled toinformation and hence informationmanagement and fusion will be animportant part of our futureresearch.

Discussion

The knowledge associated withenvironmental monitoring isextensive. The technologies underdevelopment appear to be movingtowards increased reliance on massspectrometry, for increasedsensitivity and selectivity,miniaturisation, real time response,improved field collection technologycombinations, automation andstand-off detection.

The UK has access to many of thetechnologies that could be relevantto Treaty verification and AWE willneed to engage other scientific -establishments to ensure that a truenational capability is realised. Theapproach we have adopted, and onethat was based on that successfullyused by the CTBT verification com-munity, was to send a questionnaireto relevant UK government depart-ments, industry, agencies andUniversities. The responses havebeen used to determine the level ofnational expertise of potential worthto the UK’s nuclear weapons armscontrol verification work and thelevel of interest in establishing col-laborative links and partnerships.

AWE also has a share of the UKultra-sensitive (low limit of detec-tion) technologies, including thermalionisation mass spectrometry, gaschromatography/massspectrometry, X-Ray fluorescence,electron microscopy, secondary ionmass spectrometry, alphaspectrometry, gamma and betacounting and liquid scintillation.Not all of the instruments will besuitable for nuclear weapons armscontrol research monitoringapplication as they may bededicated to certain types of work,where cross contamination withother materials would be an issue.

The existing IAEA/EURATOM/DTI Safeguards capabilities in theUK may also be of value to ourresearch if they can be adapted forenvironmental effluent monitoringof warhead-related processes. Themain radioactive materials comeinto this category, but other materi-als such as explosives and warheadspecific materials will not, although

page 37

we recognise that areas ofexcellence associated withconventional explosiveforensic assay do exist withinDERA.

The UK also has somecapability to monitorenvironmental radioactivityover wide areas by means ofgamma spectrometers onaircraft and helicopters. Thesewere utilised as part of theGreenham Common Survey,and have been used to assessCaesium-137 deposition postChernobyl.The meteorological office atBracknell also has excellentcapabilities to modelatmospheric dispersion andreleases of gases, vapours andparticulates. In addition,AWE’s in-house capability,developed to support itscrisis/consequencemanagement missions, is alsoconsidered a point of relevantexperience.

Requirements for verificationof warheads under START (Iand II) have not yet beenaddressed, the focus beingdelivery systems. IAEA/EURATOM Safeguardstechnologies and non-nuclearTreaty technologies andinstrumentation may beuseful in a future NWverification regime. Ultra-sensitive laboratorytechniques and instruments,which can measure nuclearwarhead-specific materials,will be required. In addition,portable instrumentation andminiaturised laboratory-basedtechnologies, e.g. capillaryelectrophoresis and liquidchromatography, are requiredfor OSI applications. Portableinstrumentation that can giveinstant field answers will bemore timely and avoidsecurity and transportdifficulties for collectedsamples.

In conclusion, in this chapterwe have touched upon therole that environmental moni-toring techniques may play ina Treaty. In particular, the partthat such technologies andtechniques may have inverifying that a State Party isoperating in accordance withits Treaty obligations at anintegrated weapon complexlevel. In isolation, however,like NDA technologies, envi-ronmental monitoring willlikely have limited scope fordirectly verifying a nuclearweapons arms controldismantlement process.Finally, we consider that datafusion techniques will beneeded to ensure that thevalue of all availableverification information isappropriately realised.

page 38

During the preparation of thedetailed report, an extensive list oftechnical and systems studies relatedto nuclear weapons arms controlverification research has beenidentified. This section captures theproposed programmatic frameworkfor the first year of work in theresearch phase (1st April 2000 to 31stMarch 2001). It is clear that the firstyear’s programme is by necessity ofa foundation nature as well as actingas the year in which potentiallonger-term collaboration andpartnering is explored.

Creation of a focus forverification research

The benefit of establishing a clearlyrecognised nuclear weapons armscontrol research programme,directed towards scientific andtechnical verification, is that it willcreate a focus within the UKcommunity. It will hopefullystimulate the realisation of acoherent UK approach. Such a focuswill need to straddle manycommunity boundaries. Lead agen-cies in HMG, for instance MoD, DTIand FCO, have an interdependentrole to play as part of the UK’snational security programme.

Without a clear focus within AWEthere is a strong possibility that theverification research work willflounder as a collection of decoupledtasks. For this reason it has beenproposed that a VerificationResearch Programme (VRP) becreated at AWE.

The VRP will initially have threeprime foci:

4 Arms control/reduction verification technical research;

4 Arms control/reduction verification studies;

4 Continuance of enduringCTBT research work.

The Verification ResearchProgramme will also help withvisibility of the programme outsideof AWE, thus facilitating andencouraging external involvement,for instance links with MoD, OtherGovernment Departments, acade-mia, industry and Non-GovernmentOrganisations.

Proposed Arms Control VerificationResearch Programme

Veri

ficati

on

ResearchPro

gra

mm

e

Scie

ntific

&

technical Arms

Red

ucti

on

page 39

Outline programme

From the main text, we haveidentified five theme areas forthe research phase of thenuclear weapons arms controlverification researchprogramme, which, wherepossible, we intend to align bycrosscutting projects. The fivetheme areas are:

4 Stockpile Status. Focusing on technologies and processes that may be used to estimate or transparently demonstrate a State Party’s stockpile of nuclear warheads and fissilematerial components, their provenance, and thesignatures associated with a State Party’s weapon complex;

4 Authentication. Focusing on technologies and processes directed at authenticating a nuclear warhead or fissilematerial component, whilst not compromising proliferation or national securityconcerns;

4 Dismantlement. Focusing on the technologies and processes that may be used to achieve verifiable dismantlement of nuclear warheads without compromising national security or proliferation;

4 Disposition. Focusing on the technologies and processes that may be used to achieve verifiable

and irreversible disposal of nuclear components andmaterials withoutprejudicing or compromising national security or proliferation.

4 Verification Systems Performance. Focusing on studies addressing theintegrated nuclear weaponsarms control regime issues.

From the work undertaken inthe study phase, we haveidentified a suite of tasks andstudies that we propose toundertake in the first year ofthe research phase (1st April2000 to 31st March 2001).Some of the work will alsoendure in subsequent years.

In order to strengthen thefocus of the work, we havecreated three projects for the2000-2001 programme:

VerificationSystems

Performance

Assert

Stoc

kpile

Sta

tus

Auth

entic

atio

n Dismantlem

entDisposition

Emerge

Renew

page 40

The ASSERT Project - Authenticationof Stockpile Signature Evidence byRadiometric (and other)Technologies. This project will formthe focus for work and studiesassociated with ‘foreground’verification technologies andprocesses that operate at thewarhead level. In addition to‘generic’ studies on (full spectrum)non-destructive assay and evalua-tion technologies, the project willmake use of the unique opportunityoffered by the Chevalinedismantlement programme. TheChevaline experimental campaignwill allow the UK to gather real-world statistical signatureinformation at all stages in thedismantlement process, from roadtransport carriage receipt of thecontainerised warhead to storage offissile material. The project willallow the chain of custody questionto be assessed in an operationalcontext. This data, together with thatgathered in future campaignscarried out on Trident on anopportunity basis, will create aunique UK database linked to thewarhead authentication challenge.The work when coupled with thedata fusion work in the RENEWproject, described below, will allowunderstanding of potentialauthentication and trackingprocesses, the effect on sensitivity ofancillary equipment (e.g. containers)and the design proliferationconcerns that authentication maycreate. The ASSERT project will alsoact as the focus for work associatedwith assessing the impact ofpotential Treaty warhead designs ontechnical verification. Finally,although biased towards radiometrictechniques the ASSERT project willact as a focus for all technologies

and techniques aimed atauthentication and chain of custodytracking at the warhead level.

The EMERGE Project - EnvironmentalMonitoring Evidence from Regionaland Global Emissions. This projectwill be the focus for work andstudies associated with ‘background’verification technologies andprocesses that may operate at thenuclear weapon complex level. Workwill include the role of effluentmonitoring during dismantlementand thus, like the ASSERT project,make use of AWE’s operationalprocesses associated with Chevaline.The EMERGE project will supportthe infrastructure dismantlementverification question at a technologylevel, to complement the RENEWproject’s focus on verification at thenuclear weapons arms control level.The project will not be limited toradiometric techniques and will bebased on a broad portfolio oftechnologies.

The RENEW Project - REcovery ofNuclear Evidence on Warheads. Thisproject will be directed towards, andfocus work and studies related toverification, transparency andconfidence building processes thatmay operate at the integrated Treatylevel. Together with other AWEwork, the project will investigate theissues associated with the historicalrecovery of documentary evidenceon SNM material and warheadsystems, as part of any confidencebuilding, transparency andverification Treaty process. Use willbe made of the Chevalinedismantlement programme as a testbed to study, in ‘real time’, recordkeeping needs for verificationpurposes. Recommendations will be

page 41

made regarding (historical)information-based verificationthat may have utility for afuture global Treaty. TheRENEW project will alsostudy the issues associatedwith invoking a nuclearweapons arms control regime,within which an arms reduc-tion process may take place.Finally, the project will act asa focus for transparencystudies associated withhistorical (decommissioned or‘mothballed’) nuclearwarhead Infrastructures.

Discussion

Following our study phase wehave identified the content ofa Verification ResearchProgramme at AWE andplaced this work in a widerThreat Reduction context. Theproposed research pro-gramme, reflecting the imma-turity of the nuclear weaponsarms control research withinthe UK, will in the first yearbe of a foundation nature. It is our intention that thework is not restricted to AWE

and that appropriate partner-ships be developed with otheragencies.Finally, we have identifiedthree projects for 2000 whichwill focus a broad science andtechnical programme onnuclear weapons arms controlverification research.

page 42

Introduction

The previous sections of this paperhave addressed some of the issuesassociated with achieving averifiable nuclear weapons armscontrol regime.

The 1998 Strategic Defence Review,however, reiterated the integratednature of HMG’s approach tonational security. With the globalchanges that have occurred over thepast few years, coupled with thestrategic definition of nationalsecurity identified in the SDR, theopportunity for a wider review ofhas been timely.

In the study phase we haveaddressed how the emerging nuclearweapons arms control researchintegrates into an existing AWEwork by:

4 complementing work that isalready taking place; and

4 build on supporting national security of the warheadknowledge and experience that resides at AWE to establish anational science and technology capability to address the wider global nuclear weapons armscontrol and non-proliferation questions.

AWE’s deterrent mission is focusedthrough two interdependentprogrammes:

4 Stockpile Management - ensuring the appropriate number of warheads in the stockpile;continuing certification of the stockpile; refurbishment of the

existing stockpile; andwithdrawal anddecommissioning, when required, of warheads from the stockpile.

4 Stockpile Stewardship - ensuring that appropriate skills andknowledge are maintained to underwrite the stockpilemanagement mission; undertake research on nuclear warheadphenomenology to ensure future support to the existing stockpile; and maintain a capability to design and produce a successor system to Trident should one be requested by HMG.

AWE’s Threat Reduction missionintroduces a third programme thatencompasses the interrelated tasksthat address non-proliferation,export and arms control,verification, and crisis/consequenceresponse. Threat Reduction is thusthe complement to the stockpiledeterrent component of the UK’snational security programme.Together, all three programmes cre-ate an integrated and interdepen-dent mission for AWE, directedtowards supporting MoD’s nationalsecurity objectives on behalf ofHMG.

Nuclear weapon Threat Reductionalso provides a counterpart to othernuclear-related national securitymissions within HMG, such as theDepartment of Trade and Industry’sSafeguards mission associated withnon-military nuclear material. Thisrelationship, between the weaponand non-weapon parts of nationalsecurity, is one that needs to berecognised. The two areas arecomplementary and need to haveappropriate interfaces.

Threat Reduction Perspective

page 43

The world presents a complexand volatile environment,hence whatever is definednow as the Threat Reductionmission will, almost certainly,evolve over time, reflectingthe state of nuclear weaponsarms control, multilateral andinternational treatynegotiations and emergingthreats. Nevertheless, bybringing closer together theexisting complementarycomponents of the UKwarhead national securitywork, with the new nuclearweapons arms controlverification programme, astrengthened ThreatReduction focus will berealised.

A focused mission

The SDR-directed nuclearweapons arms controlresearch programme extendsweapon-related verificationbeyond the two operationalThreat Reduction programmesthat currently exist:

4 Nuclear Material Control and Accountancy - the national verification and operational deployment of MoD control andaccountancy processes for military nuclear materials;

4 Comprehensive Test Ban Treaty - the UK’scommitment tointernational verification of the compliance of the ban on nuclear warhead testing and support to the Comprehensive Test Ban

Treaty.The above two verificationprogrammes, together withanalysis support programmes(addressing understandingthe threats and vulnerabilitiesto national security) andcrisis/consequence responseprogrammes (addressing theoperational response ifcontrols are compromised)form the four main elementsof AWE’s current ThreatReduction related work. Thenew nuclear weapons armscontrol research work will beintegrated and aligned withthis enduring work.

Interfaces

It is clear that such a broadprogramme perspective willrequire specific interfacemanagement. There are goodreasons to ensure programmealignment between the MoD,other GovernmentDepartments and AWE. In thestudy we have identifiedspecific mechanisms toachieve this alignment.

Government-to-Governmentexchanges

At the moment there is limit-ed nuclear weapons arms con-trol verification research inter-change between AWE andother (government to govern-ment sponsored) internationalpartners. It is believed that thecreation of such a collabora-tive exchange will bring:* A stronger UK linkage withNational SecurityProgrammes of other Nations,

focused on non-proliferationand nuclear weapons armscontrol;

4 Clarity to collaborative objectives and goals in this subject area;

4 A recognised point of commitment to promoting international exchange;

4 Accountability forcollaborative action and programmes.

Other links

There is obvious linkagebetween the AWE ThreatReduction programme andmany external communities.Although AWE’s warheadknowledge and experience iswide reaching, we wish todevelop relationships withother agencies, both nationaland international, in order toensure that AWE is able to actas the hub of an appropriateprogramme focused onnuclear weapons arms controland nuclear warhead reduc-tion verification.

Public interface

Finally, owing to the potentialpublic interest associated withnuclear weapons arms controlverification work, we intendto establish a proactive exter-nal approach to our emergingprogramme, covering not onlymedia access, but alsopotential educational aspectsof the programme, forexample with schools.

page 44

This paper has reviewed the currentUK capability associated with theverification of a global nuclearweapons arms control Treaty. Thestudy and this paper have focusedon nuclear materials’ measurementtechniques. In particular, we haveconsidered components within thewarhead and potential verificationtechnologies associated with non-destructive assay/evaluation,directed towards (foreground)authentication, baselining and chainof custody tracking during warheaddismantlement.

In addition, the role of (background)environmental effluent emissionmonitoring technologies, directedtowards achieving confidence inverification of the operations andstockpile of a State Party’s nuclearwarhead complex has beenreviewed.

“ Deterrence, armscontrol and Proliferationare critically important toBritain’s security”

(SDR Statement)

We consider that by adopting anintegrated approach to globalnuclear weapons arms control theUK will realise an appropriatenational capability. Confidence-in-depth could be achieved byaddressing the challenge ofverification at a system level. In thestudy phase we have identified theneed to address arms reductionwithin an overarching nuclearweapons arms control context. Webelieve this approach will illuminatethe provenance question and greatly

enhance transparency andconfidence. We intend to studyverification systems dynamicsfurther in the research phase.

The work of other agencies, whichhas addressed similar matters aspart of the NPT and CTBT treaties,has been recognised. In the researchphase we intend to investigate howknowledge, experience andtechniques from these communitiesmay be transferred to a nuclearweapons arms control regime.

It has been recognised, from thework undertaken in the study phase,that technological based interven-tions (e.g. NDA and EM) need to beseen as a source of interdependentdata from which Treaty specificinformation may be realised throughthe application of appropriate datafusion. Data from individual sourceswill be of limited value in the reali-sation of a global nuclear weaponsarms control verification regime.

The study phase of the work has bynecessity focused on AWE’swarhead experience and knowledge.Nevertheless, a national survey wasundertaken, following the approachadopted during the CTBTpreparations. This survey assessedthe related capabilities and interestin academia and industry, and thepotential for collaborativepartnerships. The results from thissurvey will be used in the researchphase.

An outline programme, composed ofthree projects and a suite of studiesand tasks, has been identified for thefirst year of the research phase. Thecase has also been made that nuclearweapons arms control verificationresearch work should be considered

Conclusions

page 45

part of a higher and strategicnational security objective,aimed at reducing the globalrisk associated with nuclearweapons. By adopting thisThreat Reduction model, theUK may assure itself that it isdealing with the nuclearweapon threat in the mosteffective manner.

A national programme,directed at reducing the global

threat associated with nuclearweapons and weapons ofmass destruction, and therealisation of global nuclearweapons arms control, willnot happen overnight.However, if a pragmatic andshared vision can beestablished on this matter,then we believe such aprogramme will follow.Finally, in order to realise acoherent and aligned nuclear

weapons arms controlverification research effort,within AWE’s integratedThreat Reduction work, wepropose that a VerificationResearch Programme shouldbe established. TheVerification ResearchProgramme will act as a clearnational focus for the newnuclear weapons arms controlverification research work.

Acknowledgements

The creation of this paper hasbeen a team effort. It hasinvolved many people withinAWE and it would not beappropriate to list any oneindividual. However, thedirect support of RobinBradley, AWE’s ChiefExecutive until March 2000,has been significant.

The paper has also involveddiscussions with colleaguesnot only in various partsMoD, for example PortonDown, DI-GI staff, PACS andACSA(N)’s office, but also theDTI and the FCO. In particu-lar, however, the team wouldlike to acknowledge the usefuldiscussions undertaken withPaul Roper, ACSA(N).

page 46

Passive non-destructiveradiometric techniques

Neutron counting

A.1 Neutron sources may consistof spontaneously fissioningmaterials such as plutonium orcalifornium or materials that emitalpha particles (most actinides arealpha emitters), closely mixed withsome light elements, from whichneutrons are ejected by alphaparticle bombardment. Actinideoxides, for example, emit (α, n)neutrons.

A.2 Neutrons are commonlydetected by gas-filled proportionalcounters or scintillation detectors(typically of plastic or glass type).The gas or scintillation mediacontain elements which capture anincident neutron to release chargedparticles which produce ameasurable electronic pulse. Theprobability of capture is greatlyenhanced when the neutron energyis very low (usually termed‘thermal’ energy) and therefore thedetector normally incorporates aneutron moderating medium suchas polyethylene to slow down theincident neutron energy by multiplescattering. The most commonelements used for neutron captureare 6Li, 10B and 3He.

A.3 Whilst scintillation detectorstend to have higher intrinsicdetection efficiencies than gas-filleddevices, the total detection efficiencyof a gas-filled counter can competewith a scintillation type byincreasing the 3He gas pressure andincreasing its physical size. There area number of ways in which the

neutron data gathered by suchsystems can be analysed.

Total neutron counting

A.4 This can provide little infor-mation, beyond establishing thepresence of a neutron source andgiving a rough lower limit to thesize of the source. This is becauseneutron shielding within a packagewill mask the true intensity of thesource. If however, the detectionefficiency is known, then the size ofthe source can be measured.

Neutron coincidence counting

A.5 There is an importantdifference between the distributionin time, of neutrons from an (α,n)source and from a spontaneousfission source. The neutrons from an(α,n) source are emitted at randomtimes, unrelated to each other,whereas neutrons from spontaneousfission sources are emitted in small,time correlated groups. The size ofthese groups is determined by theneutron leakage multiplication. Thetechnique of neutron coincidencecounting can detect the existence, orabsence, of these groups and thusestablish the presence, or absence, ofa spontaneous fission source.

A.6 In favourable circumstancesneutron coincidence counting canmeasure the mass of plutoniumwithin a package. To do this, it isnecessary to know the detectionefficiency and the nature of thematerial, i.e. the isotopiccomposition and the chemical form,metal, oxide etc. (Plutonium oxideemits a mixture of spontaneousfission neutrons and (α,n) neutrons).In order to obtain a mass value, the

APPENDIX A- Radiometric Non-Destructive Assay

page 47

neutron leakagemultiplication (M) has to becalculated from thecoincidence counting data.This parameter is determinedby the shape of the materialand by the distribution andquantity of neutron energymoderating materials. Theexplosives used in warheadsare in this category. Whencombined with otherinformation, the value of Mhelps to establish thelikelihood that the packagecontains a NW.

Neutron multiplicity counting

A.7 This technique seeks tomeasure in some detail, thesize distribution of thedetected groups of neutrons.From this distribution it ispossible, in favourablecircumstances, to determinenot only plutonium mass andmultiplication, but also theproportion of (α,n) neutronsand of fission neutrons.However the techniquerequires a neutron detectionefficiency of several tens ofpercents at least. This can onlybe obtained if detectorssurround the package. Adetector in the form of anannulus with space in thecentre for the object, a “well”counter, is usually required.The data analysis required iscomplex.

Neutron spectrometry

A.8 The energydistribution of neutrons ischaracteristic of the nature of

the source. Fission neutronshave a well known energyspectrum, which is quitedifferent from that of (α,n)sources for example.Surrounding materials willchange the spectrum in a waythat depends on the type,thickness and order of thematerials. This technique hashad limited use in the past,partly due to the difficulty ofinterpreting a spectrum.However, with the increasingpower of modest computers,and the commercialavailability of suitabledetectors and analysissoftware, it is a technique thatwarrants investigation. It isprobably true to say that ifone has a recorded spectrumof a known NW, it would bedifficult to generate the samespectrum from a hoaxeddevice.

Gamma-ray spectrometry

A.9 This techniqueinvolves the detection andinterpretation of the emittedspectrum of gamma-rays froma radioactive source toprovide information on theenergy and intensity of thegamma-ray photons. Thegamma-ray photopeakenergies of all radioactiveisotopes are well documented.These are natural constantswhich are not altered bypassage of the gamma-raythrough any materials,although attenuation canreduce the intensity of thesignal. In very many casesthere is only one isotope that

emits at a particular energy. Aproperly calibrated systemcan measure many photopeakenergies with sufficientprecision that theidentification of the sourceisotopes can be establishedwith certainty.

A.10 There is a range ofdetector families that can beapplied to this type ofmeasurement; the mainclasses employ gas-fill,scintillation andsemiconductor gamma-raydetection media. The two keyproperties that distinguishthese three classes of detectionmedia are the intrinsicdetection efficiency andachievable energy resolution.The effect of detectorresolution manifests itself as a‘blurring’ of what in theoryare a number of discretemonoenergetic gamma-rays.The poorer the resolution themore a collection of closelyspaced peak energies appearsas a single broad peak withconsequent loss of ability topositively identify theradionuclides present. Whilstthe energy resolution ofscintillation detectors aresignificantly worse thansemiconductor baseddetectors they can often bemade larger in volume thanpractical semiconductorcrystals, providing a greaterdetection efficiency. They arealso more robust than theirsemiconductor counterparts,which must be kept at liquidnitrogen temperature toachieve optimum energyresolution. Essentially each

page 48

system is comprised of a detectionhead, data acquisition electronics,and computer to control both dataacquisition and perform theanalysis.

A.11 When measuring anunknown radioactive object it isimportant for the gamma-rayspectrometry system to be able toclearly resolve the distinct energiesthat can be used for identificationpurposes. Under such circumstancesa detector based on a high puritygermanium (HPGe) semiconductorcrystal will provide the best energyresolution of all the availabledetector materials. Such HPGedetectors, used to collect highresolution gamma-ray spectra,permit a range of analyses to beconducted.

Isotope identification

A.12 High-resolution gammaspectrometry (HRGS) using a HPGedetector provides indicators of thepresence of some importantisotopes. These include 238, 239, 240,

241Pu, 235, 238U and 241Am, all ofwhich emit gamma-rays of wellknown energies. However where theemission energy is low, e.g. 235U and238Pu, it is likely that surroundingmaterials will attenuate the signal tosuch low level that detection mayrequire a long measurement time.For photopeaks that partiallyoverlap each other, there aremathematical procedures forobtaining the individual photopeakenergies and intensities. Relative isotope abundances

A.13 By measuring the ratio ofthe intensities of appropriatephotopeaks, relative isotopic

abundances can often be obtained.In particular the ratio 240Pu : 239Pucan be obtained in this way. Thesetwo isotopes have photopeakenergies that are close enoughtogether that they will suffer thesame absorption as each other inpassage through any surroundingmaterials, so that their intensity ratiowill be unchanged. This ratio isimportant for identifying warheadgrade plutonium. The ratio 235U :238U can in principle be obtained inthe same way. This ratio isimportant in identifying theuranium enrichment commonlyused in warheads. However thephotopeak energies are verydifferent, so that a differentialabsorption correction is required. Todo this requires a knowledge of thenature and thickness of allsurrounding materials. Thisinformation may not always beavailable. Also the only usefulphotopeak from 235U is of lowenergy, which will be substantiallyattenuated by surroundingmaterials. For this reason it may bedifficult to detect at all. The ratio241Pu : 241Am is related to the timesince the plutonium was separatedfrom the uranium stock, and therefore is of value in identifying theage of a NW. There are photopeaksof similar energies that can be usedfor this determination.

Differential absorption

A.14 Some radioactive isotopesemit gamma-rays of several differentenergies, for which the intensityratios are well known constants. Byobserving the intensity ratios,through intervening materials,which are likely to have differentattenuation coefficients for different

page 49

energies, an estimate may bemade of the thickness of thematerial. This procedure iscalled “differentialabsorption”. It may be ofvalue for estimating thethickness of explosive andtamper shells.

Induced gamma activity

A.15 The presence of somenon-radioactive isotopes canbe identified by the particulargamma emissions induced inthem by neutrons ((n,γ)reactions) from the fissilematerials or from an externalneutron source. These includehydrogen, carbon andnitrogen, which are importantfor identifying explosivematerials. Also, well known(n,γ) reactions occur in anumber of metals such as:beryllium, aluminium, iron,nickel, copper, which may bepresent in the construction ofa warhead.

Gamma scanning

A.16 By placing a collimatorin front of the detector, andscanning the detector acrossthe package, it is possible todetermine the spatialdistribution of a gammasource. When used with anenergy window, this wouldallow the localisation ofspecific gamma emittingmaterials, such as Pu and U.This could be of particularvalue in combination with aradiograph, in order toidentify the nature of denseregions on a radiograph.Active non-destructiveradiometric techniques

Active non-destructiveradiometric techniques

A.17 As noted in the main

text the passive gamma-rayemissions from 235U are quitelow in energy (all less than205 keV with the most intensepeak at 185.7 keV). They aretherefore subject to severeabsorption (including self-absorption) effects within bulkhighly enriched uranium(HEU) and other surroundingmaterials that may be foundwithin some NW designs.Moreover, HEU does notundergo significantspontaneous fission andtherefore, where possible, anactive approach must beadopted to induce within thebulk HEU a radiationsignature that is capable ofbeing readily detected. Betterpenetration and highercounting rates can be obtainedwith neutron interrogationand subsequent detection ofinduced fission neutronsand/or associated gamma-rays. The detected neutronsignature may be associatedwith either prompt or delayedneutron emission. There aretwo main categories of activeneutron interrogationtechnique:

i. interrogation using isotopic(steady state) radiation sources.

ii. interrogation using neutrongenerator (accelerator-produced) sources.

A.18 In both instances thegeneral features of an activeneutronic assay system are thesame, and include:

i. a source of interrogating neutrons (produced by one of the two techniques described)

ii. moderating or othersuitable material around the source to tailor the source neutron energy spectrum, the better to stimulate emissions from the sample under assay

iii. shielding and reflector material around the source

iv. a detector array, designed to detect neutron radiation from the sample withminimum response to the source radiation

A.19 When a high degree ofpenetration is unnecessary, forexample when 235U samplesare small, the interrogationsource needs to be of thermalenergy to provide the desiredmeasurement sensitivity. Forlarge 235U samples, wherepenetration by theinterrogating neutrons isnecessary to obtain arepresentative result, theneutrons are required to be ofa much higher (also termedfast) energy. With largesamples the lower sensitivityobtained with fast neutrons isoften adequate. To distinguishfissile from fertile materials(e.g. to determine 235U in thepresence of 238U), sub-MeVneutron energies below thefission threshold (~ 1 MeV) ofthe fertile isotopes must beemployed.

page 50

Steady state (isotopic) neutroninterrogation sources

A.20 The most common isotopicsources, with their energies andother characteristics are shown inthe table. 252Cf gives the highestneutron yield, but 238Pu-Li can beused whenever a weaker source willsuffice. Here, 238Pu-Li has theadvantage of lower energy, thereforeeasier shielding, moderation, andthe ability to distinguish fissile fromfertile isotopes. This source alsoemits one neutron per (α,n) reaction,thus providing a random source ofneutrons that can more easily bedistinguished from coincident(correlated) emissions resulting frominduced fission in the sample.

Neutron generator (accelerator-produced) sources

A.21 The most commonly appliedaccelerator technique is that basedon the 3H(d,n)4He reaction whichproduces monoenergetic 14.1 MeVfast neutrons. Such accelerators arecompact, employing a small tritiumtarget enclosed in a vacuum-tightaccelerator tube, easily transportableand thus capable of forming amobile interrogation assay system.The accelerator can be pulsed, withpulse repetition frequencies varyingfrom 1 Hz up to ( several kHz.Neutron output rates vary typicallyfrom ( 106 to 109 neutrons/pulse

dependent upon beam current.Accelerator tube lifetimes arenormally limited to ( 105-106 pulses.

A.22 Linear accelerators (termedLinacs) can also be used tointerrogate fissile materials. Suchsystems are generally physicallylarger than pulsed neutrongenerators and therefore not asreadily transportable, but arecapable of providing both gamma(bremsstrahlung) and neutroninterrogation sources. (The latterarise from the use of a ‘converter’material placed around the Linactarget material). Neutrons can thenbe produced in the sample as aresult of (γ,n), (γ,fission) or (n,fission) reactions. Unlike a pulsed

neutron generator, the Linacis not suitable for producingmonoenergetic neutronssince the photoneutron ener-gy distribution (arising fromthe use of a convertermaterial) is a broad one.Distinguishing inducedfrom interrogationradiations

A.23 The methods by whichinduced neutron radiations can bedistinguished from the interrogatingsource are threefold, namely:

i. Interrogate with lower energy neutrons and use a detector biased to be sensitive only to higher energy neutrons.

ii. Interrogate with a random neutron source and use a detector sensitive only to multiple events, i.e. neutrons or gamma-rays received almost simultaneously during a short time interval. As with passive spontaneous fission, induced fission produces on the average 2 to 3 prompt neutrons

Source Approximate Half-life Maximum typicalaverage enegy strength (n/s)

252Cf Fission (2 MeV) 2.6 yr 5 x 109

238Pu-Li(α,n) 0.5 MeV 88 yr 2 x 106

238Pu-Be(α,n) 5 MeV 88 yr 108

241Am-Li(α,n) 0.5 MeV 458 yr 5 x 105

124Sb-Be(γ,n) 30 keV 60 days 107

page 51

and 7 to 10 prompt gamma-rays simultaneously. Thus, coincidence countingtechniques areadvantageous for thispurpose.

iii. Interrogate the sample, remove the source, and detect delayed fission-product radiations (gamma-rays or neutrons). Fission products produce( 0.02 neutrons and 5 gamma-rays per fission during the first minute after a fission. Various techniques exist forseparating the delayedfission radiations from the source radiation, including the use of pulsedaccelerator sources, isotopic sources that are quickly removed from the vicinity of the sample and the detector at the end of the irradiation, and mechanical shutters to begin and end the irradiation. Counting delayed neutrons can begin less than one second after the end of irradiation. Delayed gamma-rays are generally countedsomewhat later (several seconds to ( 1min). Because delayed neutron yields per fission are so small,repetitive irradiation of the sample is usually employed together with high-efficiency neutron detectors.

Radiography

A.24 Radiography is theprocess by which an image isrecorded of the transmitted

intensity of a beam ofradiation. This image has,untill now, been captured on aphotographic emulsion inwhich a general darkening ofthe emulsion is associatedwith the cumulative effects ofmany individual radiationinteractions. However, suchimages can now be capturedin digital fashion usingmodern day film equivalentsbased on amorphous siliconscreen technology with theadded benefit of significantlyreduced image processingtimes, lower exposure timesresulting from improvedsensitivity, and improvedimage resolution. Digitalradiography also impliesrapid image manipulation andenhancement usingproprietary softwarepackages.

A.25 It should be noted thatwhen the object to beradiographed containsradioactive sub-components -such as in the case of a NW -the background radiationlevels produced by theseitems may well lead to a lowlevel exposure (generalfogging) of the film, thusdegrading the overall imagequality.

Gamma- and x-ray radiography

A.26 This techniqueessentially produces a pictureof the internal structure of anobject that is revealed by thepenetrative capacity of thegamma- or x-rays used as theinterrogating source.Although the most common

radiation used in radiographyare x-rays generated bystandard tubes, higher-energygamma-rays fromradioisotope sources or high-energy bremsstrahlung fromelectron linear accelerators canalso be used, particularlywhen the penetration of athick and/or dense object isrequired. Film density isproportional to the degree ofexposure and, forconventional emulsions, it isnecessary to recognise thecompromise which must bestruck between sensitivity andspatial resolution which arisesfrom the use of imageintensifier screens placed inproximity to the standardemulsion.

Neutron radiography

A.27 Low energy (alsotermed thermal energy)neutrons can be imaged bysandwiching the emulsionbetween foils of gadolinium,which exhibits a large neutroncapture cross-section. The βparticles emitted in theprompt decay of the productradioisotopes can enter theemulsion and lead to itssensitisation. Such low energyneutrons will arise frominteractions with low-Z (lowatomic number) elements,particularly hydrogenousmaterials, present in the objectand thus the radiograph isessentially a picture of low Zsub-components. Fast neu-trons from the radiographysource that do not undergointeraction in the object, orsuffer only minimal energyloss, will not appreciablyaffect the radiograph.

page 52

Information on SNM, other radioactive, and non-radioactive components likely to bepresent in a NW obtained by the application of NDA techniques (and combinationsthereof).

APPENDIX B - Nuclear WarheadComponents

InformationObtaied

Innercomponentlayout

Location andphysicalextent ofradiationsources

Identificationof SNM andother RAmaterial types

Identificationof SNM andother RAmaterial types

Quantificationof SNM(assumingevidence ofdetection ofPu or enricheduranium)

NDATechnique

Radiography

Passivescanning

LRGS

HRGS

Calorimetry+ HRGS

Limitations of Technique (In terms of confirming item statusas NW

Inherent shielding may prevent determination ofexpected internal design features crucial for confirmingNW status. Requires supplementary data, particularlyregarding type and masses of SNM components, toimprove confidence in radiographic interpretation andassessment.

Locates only those radioactive components whose passivesignatures penetrate through internal components and thewarhead casing. Accuracy to which the source extent canbe measured is dependent upon degree of collimationemployed and available measurement time. Withoutidentification of radioactive material type it is notpossible to confirm presence of SNM. Hence nosignificant improvement in confidence that item is NW.

Requires measurable passive or induced gamma-raysignature. Poor energy resolution reduces overallconfidence in the identification process. No ability todetermine isotopic/enrichment data.

Requires measurable passive or induced gamma-raysignature. Although superior energy resolution(compared with LRGS) yields high confidenceidentification, the quality of isotopic and enrichmentdeterminations is dependent upon the magnitude ofpassively transmitted gamma-rays in selected energybands.

Long measurement time associated with time taken toreach thermal equilibrium. Technique cannot confirm thatall heat generated is attributable to the presence of Puunless independent assessment of Pu mass is available.

page 53

InformationObtaied

Identificationof non-RAcomponents

NDA Technique

Active neutroninterrogation +HRGS

Passive totalneutroncounting +HRGS

Passive neutroncoincidencecounting +HRGS

Passive neutronmultiplicitycounting +HRGS

HRGS

Limitations of Technique (In terms of confirming item status as NW

Induced neutron response is a complex function of item design(since this impacts interrogating neutron energy spectrum andhence the degree of induced fission achieved). Hencequantification of 235U (and hence total U using HRGS-derivedenrichment factor) is extremely difficult. Measurementsensitivity and data interpretation also impaired by likelypresence of spontaneous fission background (due to Pu).

Requires a priori knowledge of SNM chemical form, neutronmultiplication and neutron detection efficiency to determine240Pu mass and thence total Pu mass from HRGS isotopic data.

Still requires two of the above parameters to be known todetermine Pu mass. Technique requires typical neutron detec-tion efficiency of ( 1% or more. (In practice commercial wellcounters exhibit 10-20% efficiency).

Still requires one of the above parameters to be known todetermine Pu mass. Technique requires detection efficiencysignificantly in excess of that available for standard commercialcoincidence well counters.

Secondary gamma-ray production rates are a complex functionof item design. but do not preclude simple elementalidentification. Analysis may yield further detail on item design,e.g. explosive composition and thickness (the latter quantityobtained from neutron measurement data) and the presence ofreflecting material consistent with most NW designs.Substitution of non-RA components would be easily identified.

page 54

This Appendix discusses the confidence associated with various dismantlementstates arising from use of radiation signatures

APPENDIX C - RadiationSignatures

Serial

A

B

C

DismantlementState

High explosiveand SNM of 1st-stage removed asa single unit fromNW

As serial A butwith highexplosive andSNM nowphysicallyseparated

As serial B butwith additionalevidence thatSNM shape hasbeen severelymodified

Appropriate VerificationSignature Measurements

i) Examine NW gammaspectrum to confirmreduction (and in somecases total loss) of SNM-generated photopeaksand (n,γ) components.

(ii) Monitor NW forchanges in neutrondetection rate, energyspectrum and neutronmultiplication.

(iii) Mass of removedSNM component andassociatedisotopic/enrichmentdata should beconsistent with pre-dismantlement values.

As per serial A for theremaining NW andremoved SNMcomponent.

As per serial A for theremaining NW andremoved SNMcomponent, supple-mented by neutronmultiplicationmeasurement and pas-sive gamma-rayimaging of the shape-modified SNMcomponent.

AssociatedConfidence Level

Overall confidence that NWcan be considered dismantledis HIGH.

Safety considerations wouldlead to immediate physicalseparation of SNM and highexplosive with the resultantSNM in a form suitable forstorage (as is) or could besubject to further reworkingto destroy classified shape.Accountancy and physicalprotection controls equivalentto IAEA Safeguards could beapplied to classified shape.

Overall confidence that NWcan be considered dismantledis greater than Serial A. Gamma-ray spectrum of SNMcomponent will show,through diminished (n,γ) peakamplitudes, evidence of highexplosive removal.Controls as for Serial A can beapplied to the SNMcomponent.

Overall confidence that NWcan be considered dismantledis better than Serial B.Supplementary measurementsyield evidence for reducedneutron multiplication andSNM shape(s) incompatiblewith the requirements ofgeneric NW designs.SNM form readily acceptableinto conventionalaccountancy and physicalcontrol regimes applied under IAEA Safeguards

page 55

Numerous references wereused during the study phase.The following records some ofthe sources used in creatingthe detailed report:

1. Controlling Nuclear Warheads and Steps Towards a Comprehensive Regime, Keeny, S.M., Panofsky, W.K.H., Arms Control Today, 3, Jan/Feb 1992.

2. Reversing the Arms Race, Von Hippel, F., Sagdeev, R.Z., Gordon and Breach Science Publishers, 1990.

3. Halting the Production of Fissile Material for Nuclear Weapons, Delpech, T., Dunn, L.A., Fischer, D., Sood, R., Research Paper No 31, UNIDIR, 1994.

4. Dismantlement and Irreversibility, Gooby, J., Day 2 of the meeting on the Future of Russian -US Strategic Arms Reductions: START-III and Beyond, Feb 1998, available on the Internet atwww.armscontrol.ru/start/.

5. Fetter, S., Nuclear Archaeology: Verifying Declarations of Fissile Material Production, Science & Global Security, 3, 237, 1993.

6. Pillay, K.K.S., Disposition Scenarios and Safeguardability of Fissile Materials Under START Treaties,

7. Bunn, M., The US Program for Disposition of Excess Weapons Plutonium, International Symposium on Nuclear Fuel Cycle and Reactor Strategies: Adjusting to New Realities, 324, 79, 1997

8. Office of Non-proliferation and National Security, Arms Control and Non-proliferation Technologies, ‘Radiation Detection’, DOE/NN/ACNT-97, 1997.

9. Office of Non-proliferation and National Security, Arms Control and Non-proliferation Technologies, ‘The threat of Nuclear Smuggling’, DOE/NN/ACNT-96AB, 1996.

10. Office of Non-proliferation and National Security, Arms Control and Non-proliferation Technologies, ‘Co-operative Remote Monitoring’, DOE/NN/ACNT-95D, 1995.

11. W E Kane et.al., Theapplication of HRGS to Nuclear Safeguards, Non-proliferation, and Arms Control activities, Proceedings of the Institute of Nuclear Material Management 38th Annual Meeting, Phoenix, Arizona, 20-24 July, 1997.

12. J F Morgan, Transparency and Verification Options: An initial analysis of

approaches for monitoring warhead dismantlement, Proceedings of the Institute of Nuclear Material Management 38th Annual Meeting, Phoenix, Arizona, 20-24 July, 1997.

13.P E Fehlau, An Applications Guide to Pedestrian SNM Monitors, LA-10633-MS, February 1986.

14.P E Fehlau, An Applications Guide to Vehicle SNM Monitors, LA-10912-MS, March 1987.

15. IAEA Safeguards Enhancement by Remote Sensing Satellites, Jasani et al, ESARDA BulletinNo. 27, p76.

16. Canberra Commission on the Elimination of Nuclear Weapons, Report of the Canberra Commission, Department of Foreign Affairs, Commonwealth of Australia, 1996

17.The Strategic Defence Review, July 1998

18.An Alternative Framework for the Control of Nuclear Materials, Robert Rinne, Center for International Security and Co-operation (ISBN 0-935371-55-9)

APPENDIX D - Sources

page 56

There are many terms associated with the nuclear weapon and warhead communitiesthat deserve clarification. Whilst every effort has been made to ‘spell out’ acronyms,there always exists the possibility that ‘strange language’ has crept into the paper. Forthis reason the lay reader may find the following glossary and list of acronyms helpful.

Term Definition93+2 See IAEA 93+2ACSA(N) Assistant Chief Scientific Adviser (Nuclear)ARS Acoustic Resonance Spectroscopy. A technique in which the

acoustic resonance signature of an object is used to infer itsphysical make-up

AWE Atomic Weapons EstablishmentBaselining Using information, such as process records or Signatures, to

determine the expected measurements from a plant, process or object. Baselines establish a verified source from which process changes or deviations may be detected

CCTV Closed Circuit TelevisionChain of Custody A process of contiguous accountability from a point of

known provenance.Confidence Building In general the release of information or the undertaking of

activities, through voluntary, co-operative and transparent processes, to show good faith and increase confidence.

CTBT Comprehensive Test Ban Treaty CWC Chemical Weapons ConventionData Fusion The process of associating, correlating and combining data and

information from multiple sources.Dismantlement To take apart a nuclear weapon (not necessarily irreversibly) prior

to final material disposition.Effluent Materials such as gas, solids (particulates), liquids and vapours

emitted from an operational plant or facility.Emission An effluent or some physical signal, from a plant or facility. This

includes radiation.ESARDA European Safeguards Research and Development AssociationEURATOM The European Safeguards Office based in Luxembourg implement

safeguards in the EU, pursuant to the Euratom Treaty, to confirm that civil nuclear material is not diverted from its declared end uses.

Fissile material Materials with fission cross-sections sufficient to undergo fission in a thermal neutron fluence. e.g. U-235 and Pu-239

FM Fissile MaterialFMC Fissile Material Component. A component of a warhead made

from or with fissile material.H-bomb Bomb relying on fission in a 1st stage to drive fission and

fusion in a 2nd stageHEU Highly Enriched UraniumHPGe High Purity GermaniumHRGS High Resolution Gamma SpectroscopyIAEA International Atomic Energy AgencyIAEA 93+2 A programme set up by the IAEA after the discovery

of the Iraqi nuclear programme, which identifiedtechnologies and procedures to strengthen detectionof horizontal nuclear proliferation. Manyenvironmental technologies were added to theverification regime

IMS CTBT International Monitoring SystemIn-Field Technique Technique that can operate with equipment that can be

transported to a location to take measurements andprovide data

In-situ analysis Analysis carried out at the sample locationINF Intermediate Nuclear Forces TreatyINMM Institute of Nuclear Materials ManagementIsotopics The proportion of a particular isotope in a mixture of an element

APPENDIX E - Glossary

page 57

Laboratory Technique Technique that requires equipment based in a fixed laboratory, socollected samples are transported for measurement

LEU Low Enriched UraniumLIDAR Light Detection and Ranging: using reflections from a laser beam to measure characteristics of cloudsLRGS Low Resolution Gamma-ray SpectroscopyMOD Ministry of DefenceMOX Mixed Oxide Fuel - U and Pu oxideMPC&A Material Protection Control and AccountingNAA Neutron Activation AnalysisNaI Sodium Iodide - a sensitive, low resolution gamma ray detector materialNDA Non-destructive assayNDE Non-destructive evaluationNGO Non governmental organisationNPP Nuclear Physics Package, the part of the weapon containing the fissile material components, and that

part that produces the nuclear yieldNPT Non Proliferation Treaty.NTM National Technical Means. Technologies supported and practised at a State level in support of

intelligence-gathering Nuclear weapons cycle The stages of design, materials production, component manufacture, assembly, deployment into

service, maintenance, disassembly and disposal including transport and safety aspects, that comprise the nuclear weapon system.

NW Nuclear weapon or nuclear warheadNWS Nuclear Weapon StateNWFZ Nuclear Weapon Free ZoneOSI On site inspectionOvert Visible, undisguised and observable; undertaken with the knowledge of the State from whom the

information is gathered.P5 US, UK, Russia, France and China - the declared or de jure nuclear weapon statesPACS Proliferation and Arms Control Secretariat within MoDPhysics Package The part of the nuclear weapon containing the fissile material components, also called the NPPPit Stuffing A term used to cover techniques associated with physically disabling the ability of the

fissile assembly of a warhead to become critical under implosive conditions.Proliferation Used in two senses. The horizontal proliferation of nuclear weapon related information or materiel to

another nation. Vertical proliferation involving the acquisition of knowledge by a Nuclear Weapon State designed to take that State’s weaponunderstanding to a higher level, for example fission to fusion.

Provenance The stockpile source of a warhead or component being verifiedPTBT Partial Test Ban TreatyPu PlutoniumRemote Monitoring Monitoring using instruments which can operate without attention.Remote real time As above but providing a continuous record of a measurement monitoringSafeguards Processes and mechanisms under the control of the IAEA or EUATOM to account for nuclear

materials. Safeguards do not cover nuclear weapons related fissile material stockpilesSDR Strategic Defence ReviewSignature The chemical, isotopic or physical characteristics that identify a particular material,

assembly or process.SNM Special Nuclear Material. A material containing fissile nuclides.SSS Strengthened Safeguards System, consisting of existing IAEA safeguards measures demonstrated by

93+2 to strengthen the effectiveness and improve the efficiency of the safeguards system.START The US-Russian bilateral Strategic Arms Reduction TreatyTransparency In general a process directed at the voluntary or co-operative release of information to improve

confidenceTTBT Threshold Test Ban TreatyU UraniumUN United NationsUNSCOM United Nations Special CommissionVerification Authentication and validation of a State’s compliance to a TreatyWMD Weapon of Mass Destruction. A generic term associated with nuclear, biological and chemical weapons

and devices.

© Crown Copyright 2000“The right to prevent or restrict copying of this Crown Copyright document is dispensed

with. The contents of this document may, however, not be modified or reproduced in part ifsuch activity results in the material giving a different impression compared to that in the

entire and unmodified document”.

Designed and Produced by Media & Publishing Group