T 55A The Actinide Research Quarterly · seams on a soccer ball. Fullerenes and their discoverers, Richard E. Smalley, J. R. Heath, S. C. Scientists Study the Use of Fullerenes to

1Nuclear Materials Technology Division/ Los Alamos National Laboratory

TA55

• A U.S. Department of Energy Laboratory

The Actinide Research

Winter 1997 Los Alamos National Laboratory

o f t h e N u c l e a r M a t e r i a l s T e c h n o l o g y D i v i s i o n

Quarterly

In This Issue

1Scientists Study theUse of Fullerenes to

Trap Actinides

3High-Level PoliciesImpact Stewardshipof Excess Plutonium

5On the Disposal of

Plutonium

6Fabrication of Zircon

Leads toa Pu Stabilization

Alternative

9Ph.D. Thesis

Explores SodiumZirconium Phosphate(NZP) Waste Forms

for Actinide Disposal

11Recent Publications,Presentations, and

Reports

12NewsMakers

Fullerenes are anew class of carbonmolecules, the firsttruly molecular formof pure carbon yetisolated. Fullerenesconsist of hollowcages composed ofthree-connectednetworks of carbonatoms. The namefullerene was chosento honor R. Buck-minster Fuller, thecreator of the geo-desic dome, andfullerenes are alsoknown as “bucky-balls.” The mostfamous fullerenemolecule, C60 or“buckminsterfullerene,”has sixty carbonatoms arranged inthe same geometryas the vertices of theseams on a soccerball. Fullerenes andtheir discoverers,Richard E. Smalley,J. R. Heath, S. C.

Scientists Study the Use of Fullerenes to Trap Actinides

metallofullerene(a metal atom withina closed-cage fuller-ene). In fact, withina few days of theoriginal realizationthat C60 may beshaped like a soccerball, the first experi-mental indication wasobtained that a metalatom can be putinside. Smalleywrites, “For mostobservers on firstlearning of the pro-posed soccer ballstructure of C60,there often is analmost irrepressibleurge to ask ‘Canyou put somethinginside?’” We asked,“Can you put anactinide inside?”Here was an oppor-tunity to trap actinideatoms within one ofthe most stablemolecules or clustersever encountered and

Figure 1. An idealized structure of U@C 60.*The uranium atom in the center of themolecule is too large to fit through any ofthe holes in the five-membered and six-membered carbon rings that make up thefullerene cage. It is expected that the truestructure of U@C 60 will have the uraniumatom off-center as the hollow within thecage is much larger than the uranium atom.It is also expected that the uranium atomwill donate electrons to the cage and existwithin the cage as an ion although themolecule as a whole will be uncharged.

O’Brien, and Robert F. Curl of Rice Universityand Howard W. Kroto of the University ofSussex, England, were honored this fall by the1996 Nobel Prize in Chemistry, eleven yearsafter their discovery.

The cage-like structure of fullerenes canbe used to encapsulate metal atoms on amolecular scale creating an endohedral

isolate it chemically from its environment.The first application to occur to us was to

use endohedral metallofullerenes as the basisfor a superior waste form for actinides. Anencapsulated actinide atom cannot escapefrom its fullerene cage—the holes in the cageare too small even for a helium atom to fitthrough. The problem of a stable waste form

[*See Note p.2]

2 Nuclear Materials Technology Division/ Los Alamos National Laboratory

The Actinide Research Quarterly

Scientists Study the Use of Fullerenes to Trap Actinides(continued)

is reduced to the simpler problem of theimmobilization of the much larger andhydrophobic fullerene with the actinidetrapped inside. In all conventional wasteforms, metal ions have mobility and can beleached out of the matrix. The migration ofa metal atom trapped within a fullerene isexpected to be much lower because the wholefullerene must migrate for the trapped metalatom to move.

Our interest in this approach was stimu-lated in 1991 by a string of discoveries infullerene science. The first and most significantdiscovery was made at the University ofArizona by Huffman and Krätschmer, whodeveloped a method to produce macroscopicquantities of fullerenes in a carbon arc. Beforethis discovery was made, fullerenes werestudied by sweeping the vapor created by anintense laser pulse, which had been focusedonto a carbon target, into a sensitive massspectrometer. The second discovery was thedetection of fullerenes in Precambrian rockbelieved to be more than 600 million years old.Fullerenes thus appear to have been chemi-cally stable in the environment for muchlonger times than those required for aplutonium waste form. The third discoverywas of a uranium endohedral metallofullerene,U@C28, whose efficiency of production wasmuch greater than other endohedralmetallofullerenes. The relative absence ofempty fullerenes, the authors conclude,suggests that fullerene cages are to someextent actually nucleated in the gas phasearound uranium atoms or ions. One couldnot only make actinide endohedralmetallofullerenes, but the productionefficiency was much higher when the metalwas an actinide than it was for other metals.

Investigations of endohedral metallo-fullerenes have been plagued by low produc-tion efficiencies, sensitivity of the endohedralfullerenes to air, and a lack of separationmethods to isolate a pure product. The lastdifficulty arises from the fact that endohedralfullerenes, with the single exception of M@C82,are insoluble in all solvents. We have built acarbon arc apparatus for the production ofactinide metallofullerenes under anaerobicconditions. We have developed a sublimationmethod for the separation of metallofullerenesfrom the “soot” produced in the carbon arcand, by careful control of the temperature,have accomplished separation of metallo-fullerenes from empty fullerenes. A thin filmcan be made by subliming fullerenes onto atarget. Certain carbon atoms can be removedpreferentially by sublimation at relatively lowtemperatures, leaving the metallofullerenes inthe soot. The U@C60 is sublimed after theempty fullerenes have been removed from thesoot by raising the temperature by just a fewdegrees. The ability to produce relatively purefilms of metallofullerenes will allow theinvestigation of their chemical and physicalproperties.

Safe production and manipulation ofactinide-containing fullerenes has beendemonstrated using anaerobic handlingtechniques. Sublimation of empty andendohedral metallofullerenes has provedits utility as a technique for separation offullerenes into cage-size groups. This allowsthe preparation of films containing only C60,C70, and M@C60 as well as films greatlyenriched in higher fullerenes relative to C60and C70. The temperatures required forsublimation of M@C60 indicate that itsenthalpy of vaporization is a few kcal/molhigher than C60, the likely result of strongerinteractions between M@C60 and itsenvironment in the soot.

Collaboratorson this projectinclude MichaelD. Diener, RiceUniversity; andColeman A.Smith, JamesT. McFarlanand D. KirkVeirs, NMT-6.

[*Note on nomenclature: A molecule identified as a fullerene always has a closed-cage structure.Endohedral metallofullerenes are written as M@CX where M is the metal, @ indicates that the metal isinside the fullerene cage as opposed to being bound to the outside of the cage, and X indicates that thefullerene cage is composed of X carbon atoms.]


Winter 1997

On March 1, 1995, President Clintonannounced the withdrawal of 200 metric tonsof fissile materials from the United States’nuclear weapon stockpile, declared that thismaterial was excess to the U.S. nuclearsecurity and defense needs, and publiclycommitted that these excess materials wouldnever again be used for nuclear weapons.This excess fissile material includes 38.2metric tons of weapons-grade plutoniumin addition to a total of approximately 14.3metric tons of fuel-grade and reactor-gradeplutonium. Thus, based on U.S. governmentnonproliferation policies, the U.S. presentlyhas a nominal 50 metric tons of "excessplutonium," which it must manage anddispose of in the future. (Note that this 50metric tons is approximately one-half the totalplutonium inventory currently existing atDepartment of Energy (DOE) sites and withinassembled nuclear weapons in Department ofDefense—DoD—custody).

The developing nonproliferation policy ofthe U.S. government, along with the changingroles and responsibilities of the various DOEprogram offices, will have major impacts onhow the DOE will manage the excess pluto-nium inventory in the future. In turn, thesedeveloping policies, along with guidance andrecommendations for materials managementfrom cognizant DOE program offices, willsignificantly impact how Los Alamos will berequired to manage and control its excessweapons-grade plutonium inventory. Thisis important to Los Alamos because of thevarious programmatic activities that requireeither excess or defense-related plutonium.For example, the DOE Office of DefensePrograms underwrites work at TA-55 (thePlutonium Facility) to develop the capabilityto manufacture small quantities of “warreserve” plutonium pits as part of theStockpile Stewardship and ManagementProgram. At the same time, Los Alamos isdeveloping pit-disassembly technologies (i.e.,ARIES) for dismantling the excess pits in theDOE inventory. This work is performed under

the auspices of the DOE Office of FissileMaterials Disposition (MD). Furthermore,Los Alamos is also working on technologiesassociated with the development of mixedoxide nuclear reactor fuel to make it possibleto burn plutonium in nuclear reactors, shouldthat option be chosen for disposal by DOE/MD. To make the situation even morecomplex, the DOE office of EnvironmentalManagement is evaluating the possibility ofhaving Los Alamos stabilize and processvarious plutonium-containing residues fromRocky Flats as part of the recommendationsof the Defense Nuclear Facilities Safety Board(DNFSB) 94-1 Program. The plutonium in theresidues at Rocky Flats has also been declaredexcess to national security needs by the DOE.

In preparation for President Clinton’snonproliferation policy statement in 1995,the DOE and DoD performed an exhaustivereview of exactly what fissile materials will berequired to meet future U.S. national securityneeds. One result of that review was theidentification of excess-plutonium-containingitems that make up the 38.2 metric tons ofexcess weapons-grade plutonium at thevarious DOE facilities. This review identifiedspecific plutonium pits in DOE custody at thePantex Plant and at Rocky Flats, as well asexcess pits in weapons that are currently inDoD custody and are awaiting return to theDOE for dismantlement. Since the Presidenthas declared that this plutonium has beenpermanently withdrawn from the nation’snuclear weapon stockpile and will neveragain be used for national security programs,it is prudent to ask the following questions:How do we ensure that the President’s statednonproliferation policy will not be compro-mised since TA-55 uses both excess plutoniumitems and defense-related plutonium items?Will additional controls and/or inventoryaccounting procedures be required for theplutonium removed from excess pits duringARIES prototype development to ensureconfidence that the plutonium will not beused in defense-related activities? Will it benecessary for all excess plutonium at LosAlamos to be physically segregated from the

High-Level Policies Impact Stewardship ofExcess Plutonium

The ideaspresented in thiseditorial are theauthor's and donot necessarilyrepresent theopinion of LosAlamos NationalLaboratory, theUniversity ofCalifornia, theDepartment ofEnergy, or theU.S. Government.

Guest Editorial

Robert G.Behrens of theNuclear Materi-als and Stock-pile Manage-ment ProgramOffice is pres-ently on assign-ment with theDOE Albuquer-que Field Of-fice, WeaponsQuality Divi-sion, NuclearTechnologyBranch. He canbe reached at(505)845-6263.



plutonium used in pit fabrication and otherdefense-related projects? If so, how would thisbe implemented at TA-55 and at what cost interms of facility space, duplication of proces-sing facilities, and additional materials controland accountability, etc.? Will the DOE allowexcess plutonium to be substituted for nationalsecurity plutonium as well as vise versa? If so,how will the DOE provide assurance to thepublic and to special interest groups thatexcess plutonium is not being reused fornational security purposes after the Presidenthas publicly stated that it has been perma-nently withdrawn from such use? These areimportant questions that must be addressedadequately by DOE and Los Alamos nuclearmaterials managers from the perspectives ofoperations, logistics, and politics.

President Clinton’s nonproliferationpolicies also give rise to a second major issueof interest to Los Alamos—the voluntarysubmittal of excess plutonium by the U.S. tothe International Atomic Energy Agency(IAEA) for inspection, as promised by thePresident. Most recently, on September 17,1996, the U.S., Russia, and the IAEA held atrilateral meeting concerning IAEA verifica-tion of fissile material originating fromweapons. Consequently, the DOE has decidedto make international safeguards of U.S. excessfissile materials a routine factor in its planningand budgeting. It has recommended that 15.4metric tons of excess plutonium beingstabilized in the DNFSB 94-1 Program shouldbe made available for IAEA inspection. It hasalso recommended that a long-term plan forsafeguarding U.S. excess fissile materialshould be coordinated with the IAEA, andit is currently taking action to develop animplementation plan and to evaluate thepotential availability of plutonium that can beoffered for IAEA safeguards. This last actionincludes consultations between the DOEOffice of Nonproliferation and the DNFSB 94-1stabilization program as to how, where, andwhen this material should be placed underinspection.

As a result of this planning, excessplutonium residing at Los Alamos couldconceivably be made available for IAEAinspection in the future. Plutonium removedfrom excess pits during ARIES prototypedevelopment and demonstration would beespecially politically attractive in this regard.Much of the weapons-grade plutonium beingstabilized at TA-55 under the DNFSB 94-1Program is not considered excess but isrequired for the development and demonstra-tion of pit fabrication. Therefore, DOE andLos Alamos managers must jointly evaluateany impacts on defense-related activities atTA-55 if any plutonium stabilized under theDNFSB 94-1 Program is considered for IAEAsafeguards. We must be confident that defense-related programs are not placed in jeopardybecause of the high-level nonproliferationpolicies coming out of DOE Headquarters.In addition, excess plutonium at Los Alamosmust be adequately controlled, readilyidentifiable, and available for off-site shipmentfor long-term storage, disposition, or place-ment under IAEA safeguards, should thepolicy makers decide to implement any ofthese actions.

Future institutional, operational, andprogrammatic issues associated with managingthe excess and defense-related plutonium atLos Alamos are complex, and the process toaddress these issues must be carefully thoughtout and effectively managed. It must ensurethat U.S. nonproliferation policies are adheredto through adequate control and accounting ofexcess plutonium as defense-related activitiesat TA-55 proceed. It is important that LosAlamos managers are aware of the politicalnonproliferation policy decisions being madein Washington while also being cognizant ofhow these policies may impact plutoniumoperations at TA-55. Clearly a renewed andincreased institutional attention to themanagement and control of nuclear materialinventories will be required to meet thechanging Los Alamos role and mission intothe next millennium.

Robert G. Behrens

“We must beconfidentthat defense-related pro-grams arenot placedin jeopardybecause ofthe high-level nonpro-liferationpoliciescomingout ofDOE Head-quarters.”


Winter 1997

On the Disposal of PlutoniumEditorial

Looking forward to the dawn of anew century and the second millenium,the Actinide Research Quarterly (ARQ)requested and was granted an audience

with Dr. Actinide to talk onthe subject of plutonium, the

“element of this century.”

ARQ: For over 50 years the nuclear nations of this world wereengaged in the race to produce plutonium for their nuclear weaponsstockpile, which, we are told, helped maintain world peace based onthe insane dogma of mutually assured destruction (MAD). With theend of the Cold War we are now rushing toward finding ways ofdisposing of what’s called “excess plutonium” from retired nuclearweapons. What are your thoughts on this element that you are all toofamiliar with in the universal element chart (our discovery number94)?

Dr. Actinide: A quite natural sequence of events although onoccasions I was quite concerned about the madness that prevailedamong some of you living through the dawn of your nuclear age.

ARQ: In addition to this urgent desire to dispose of plutonium,the following concerns seem to be of paramount importance:preventing theft and proliferation of nuclear weapons, protecting thepublic and environment from contamination, and if economicallyfeasible, using plutonium as a viable energy source to fuel furtherprogress.

Dr. Actinide: Admirable concerns for the human species and theworld’s citizens, indeed.

ARQ: But the problem of disposing of plutonium is compoundedbecause plutonium now appears mixed in many different things.Besides, plutonium present in our environment now presents acontamination hazard.

Dr. Actinide: The dispersion of plutonium is as natural as can be.Contamination is in the eyes and minds of humans. Undo the mixing ifthat’s what you wish to do. However, I would expect that you shouldnot spread plutonium any more than you’ve done already by such sillyactivities as exploding it in the atmosphere or dumping it in yourocean.

ARQ: The most commonly suggested solutions to plutoniumdisposal fall in one of the following categories: burying it, glass-logging it, burning it, mixing it, and storing it.

Dr. Actinide: Such a cacophony of nonsense. You introduced itinto the world; now that you have it, learn to live with it.

ARQ: One of the important concerns we have associated with anyof these disposal scenarios is waste generation. More so than with anyother human activity, the handling of radioactive materials inevitablyincreases waste.

Dr. Actinide: Remember all elements areradioactive on the Creator’s time scale, somemore so than others. It is nature’s law that thetotal energy of the universe is conserved.Energy can neither be created nor destroyed.An element such as plutonium, a form of thisenergy, cannot be destroyed at will. Some ofyou may argue that an element undesirable tohuman species can be transformed to a moredesirable form. But remember also that you donot control the outcome of such transformationof the elemental stuff.

ARQ: Yes, we know that we live in anenvironment of natural radioactivity and,therefore, it is unnatural to think of a“radiation-free” environment. For example,the world oceans contain, although diluted, thelargest amount of uranium, another element ofyour superb expertise. We never hear anyonesuggesting that we should clean up the oceanof its radioactivity. There’s also cosmic radia-tion and radiation in the buildings we work inand live in, the food we eat, the air we breathe.

Dr. Actinide: That’s right. You are aproduct of the earth, this wonderful place welive in. Plutonium also is here to stay with youand your children. The prudent thing for youto do is to manage and safeguard it properly sothat you can draw from it more benefit thanharm.

ARQ: Dr. Actinide, you’ll grant that’seasier said than done....

Dr. Actinide: Almost everything is.Among all things created, ironically forhumankind, plutonium may turn out to be oneof those elemental magnets that makes humanbeings all come together and cooperate to finda lasting solution to this uniquely humanproblem. That’s the challenge.

Kyu C. Kim

The ideas presented in this editorial are theauthor's and do not necessarily represent theopinion of Los Alamos National Laboratory, theUniversity of California, the Department ofEnergy, or the U.S. Government.



Fabrication of Zircon Leads to a Pu StabilizationAlternative

An article byR. Ewing (UNM)appeared in theFall 1995 issueof the ActinideResearchQuarterly. Thearticle in thiscurrent issuedescribes thework initiatedat Los Alamos.

Background and Research ObjectivesZircon, because of its well-known, long-

term durability (~109 years) in the geologicenvironment, has been proposed as a hostmedium for storage of Pu and other actinidesrecovered from dismantled nuclear weapons.Much is known about the structure of thissingle-phase mineral and its homologs (e.g.,Hf, Th, Pa, U, Np, Pu). It is clear that zircon-type orthosilicate structures can accommodate

metal cations having radii bothsmaller and larger than that of the Zr ion inzircon. Natural zircon has been found tocontain approximately 5000 ppm of U and Th.Some of the cations found in natural zircon(e.g., Gd, Hf) are strong absorbers for thermalneutrons. Laboratory-scale samples of zircondoped with up to 10 wt % of Pu have beenprepared for conducting accelerated tests onthe effect of radiation damage on the structure,property changes, and phase stability insimulated geological conditions (by W. J.Weber at the Pacific Northwest NationalLaboratory). Furthermore, small samples ofpure PuSiO4 have been prepared (by C. Kellerin Karlsruhe, Germany), which suggests that itis possible to substitute Zr with more than 10wt % of Pu. From the point of view of nuclearwaste minimization, it is desirable that the

upper limit of Pu solubility in zircon bedetermined. While exploring the potential forincreasing the Pu loading in zircon, we need toinvestigate the issues of criticality safety so thatthe optimum waste form can be determined.

Various methods for synthesizinglaboratory quantities of zircon have beeninvestigated. However, simultaneousapplication of high temperature and highpressure to enhance the solid-state reactionhas not been attempted, especially for zircondoped with large quantities of Pu. With theexisting equipment, such as hot presses and'hot isostatic presses in the Plutonium Facility,LANL is in a good position to develop thetechnology for large-scale fabrication of Pu-bearing zircon and, therefore, to provide thenation with an alternative method for dispos-ing of nuclear materials. The success of thiswork will allow us to address the technicalproblems related to short-term and long-termstorage of nuclear materials recovered fromweapons. The results of this effort will enhanceTA-55’s capabilities in solving plutoniumdisposition problems.

In this work we set out to obtain thefollowing information, essential to large-scalefabrication of Pu-bearing zircon: 1) the processparameters for large-scale fabrication of zirconwith desirable Pu-loading and 2) the solubilitylimit of Pu in zircon. What we learn will beimportant from the standpoint of minimizingwaste volumes. This article presents the resultsof the first study.

Scientific Approach and AccomplishmentsSince the main objective of this work

was to investigate the feasibility of large-scalefabrication of Pu-bearing zircon, it was ofutmost importance to be able to achieve thisgoal without releasing contamination to thework environment. Therefore, the approachtaken in this work was to use the synthesis ofzircon to explore potential problems in thecontainment of materials during processing.Furthermore, since PuO2 is thermodynamicallyless stable than ZrO2, the processing para-meters developed for the synthesis of zirconwould be applicable to those for Pu-zircon.

Figure 2. Thetantalum con-tainer after thefirst HIP run.This figureshows thatthe welds areintact, and thebody of thecontainer re-mains in goodcondition after 2hours at 1450 °Cand 4000 psi.


Winter 1997

The process used was hot isostatic pressing(HIP). The equipment provides high tempera-ture in the reaction chamber through resis-tively heated graphite heating elements. Itprovides high pressure by compressing inertargon gas supplied from gas cylinders to thereaction chamber. The hot press is capable ofattaining temperatures up to 2000°C andpressures up to 30,000 psi. The material to be“hipped” is contained inside compressiblecontainers, typically fabricated from thinmetals, and is compressed with equal forcefrom all directions.

For hipping zircon, a container made ofrefractory metal that melts at high temperatureis desirable. However, most metals arethermodynamically unstable, (and more soat higher temperatures), with respect to theformation of their oxides. Since the startingmaterials for zircon are oxides, the oxidationof the container materials is inevitable unlesssome sort of barrier (inner container) isprovided to separate the reaction mixture fromthe metal container. But this inner containermust also be compressible as well aschemically inert to the reaction mixture.

In anticipation of fabricating Pu-zircon inPF-4, the LANL Plutonium Facility, someschemes need to be developed for packagingthe reaction-mixture/container assembly. First,the powder mixture has to be loaded into theinner container inside a glove box. Then, forsafety reasons, the container has to beassembled and sealed without the use ofexcessive heat. Thereafter, this inner containerwill be transferred from a glove box into the“cold” outer metal container in an introductoryhood while the outer container is maintainedfree of contamination. The metal container willthen be welded in a separate “cold” tungsten/inert gas (TIG) welding hood. Finally, the outercontainer has to maintain its integrity after theprocessing; otherwise the process equipmentcontained inside the hood will becontaminated.

Based on these criteria, tantalum waschosen for the outer container, and quartz theinner one. Tantalum was chosen based on itshigh melting point of 3017° C, its availability,and its relative ease of welding. The choice ofquartz was based on the known phase behav-ior of the ZrO2/ SiO2 system. The phasediagram of this system indicates that zircondoes not form any compounds with SiO2 in thetemperature range of interest. Furthermore,quartz softens at temperatures above 1200°Cand, therefore, can be compressed. Neverthe-less, the potential for reactions among Ta,ZrO2, and SiO2 still exists. Based on thiscontainment system, the range of temperature,pressure, and time were explored to provide areasonable processing scheme.

Results and AccomplishmentsThe tantalum container was compressed

as expected, the welds were intact in all cases,and the quartz joint held together in one piece.The product was monolithic. The results fromx-ray powder diffraction showed that 30 lineswere observed in the starting material, andthat almost all lines can be assigned to eithermonoclinic-ZrO2 or SiO2 (quartz). In the firstHIP run, 39 lines were observed in theproduct. Out of the 39 lines, 25 are assignableto zircon, 11 are due to monoclinic ZrO2, andonly 3 are due to SiO2 (cristobalite). However,the 3 strongest lines are due to ZrO2 and SiO2.This indicates that zircon begins to form inapproximately 2 hours of reaction time, butthe reaction is nowhere near completion.The other samples from all products showedalmost identical patterns and relative inten-sities. This indicates that the extent of reactiondid not differ significantly for reaction timesranging from 2 to 8 hours. A more quantita-tive analysis is necessary using x-ray diffrac-tion on samples that are mixed with standardreference material. Further product materialcharacterization by chemical, analytical, andmetallographic techniques are underway.

Principal investi-gators are KyuC. Kim, NMT-DO, and John Y.Huang, NMT-6.Others contribut-ing to the projectare Patricia LSerrano andMark A.Williamson,NMT-6; MaryAnn Reimus,Gary H.Rinehart, Chris-tina M. Lynch,Paul Contreras,and Paul Moniz,NMT-9; StanleyPierce, MST-6;RudolphFernandez,NMT-4;McIlwaineArcher andRichard G.Logsdon,MST-7; andLuis A. Morales,NMT-5.

continued on next page



Zircon-and-Quartz Containers May Be Usedto Stabilize Plutonium for Disposal (continued)

Figure 3. Cut-up view of a tantalumcontainer after processing. The figureshows that the quartz joint holdstogether. The quartz container hasbroken into pieces and can be sepa-rated from the product.

Under the high-temperature and high-pressure conditions employed in this work,hundred-gram batches of ZrO2/SiO2 mixturebegan to react and form zircon in approxi-mately 2 hours. Considering the thermo-dynamic stability of PuO2 relative to ZrO2(i.e., PuO2 has less negative

standard Gibb’s free energy of formation thanZrO2), it is expected that the fabrication of Pu-bearing zircon will be accomplished moreeasily than the fabrication of zircon alone. Theresult of this preliminary work indicates thatit is feasible to fabricate large quantities of Pu-

zircon; however, furtherdevelopmental work is necessary.

This work revealed potentialcontainer problems that could beencountered at the developmentalstage and suggested practicablesolutions. The quartz innercontainer, the glass sealant, andthe tantalum outer container allshowed expected behavior. Theprocess developed for joiningquartz parts with the use of aspecial glass sealant, as analternative to high-temperaturefusion, inside glove boxes is aninnovative approach that isapplicable to other operationsin the Plutonium Facility. Thecontainment system allowed thereaction mixture to becompressed isostatically. The

separation of final products from thecontainer materials was not difficult. Thereactions between tantalum, SiO2, and ZrO2could be prevented by providing a sacrificialbarrier between the inner and the outercontainers. Clearly, further developmentalwork is needed to establish a safe process forlarge-scale fabrication of Pu-bearing zircon.


Winter 1997

P

Zr

Zr

Zr

Zr

Zr

Zr

P

Na+

Na+

Na+

Na+

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Na+

Na+

P

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Zr

Zr

Zr

Zr

PP

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Ph.D. Thesis Explores Sodium Zirconium Phosphate(NZP) Waste Forms for Actinide Disposal

Figure 4. The NZP structure isa three-dimensional networkof interconnected zirconiumoctahedra (red polyhedra) andphosphorous tetrahedra (graypolyhedra). The structureaccommodates cesium andstrontium ions in large inter-stitial cavities occupied bysodium ions in the parentstructure. Fission productsand residual actinides sub-stitute for zirconium asessential constituents of thethree-dimensional network.

continued on next page

The disposal of high-level radioactivewastes generated during the reprocessing ofspent fuel rods from nuclear reactors torecover the actinides is an ongoing problem forthe DOE, costing billions of dollars. Thesewastes include defense wastes currently storedat a number of locations such as the tank farmsat Hanford and the underground storage binsat the Idaho National Engineering Laboratory(INEL). Wastes generated during the reproces-sing of civilian nuclear reactor spent fuel rods(before a 1977 moratorium on reprocessinginitiated during President Carter’s administra-tion) are stored at the West Valley reprocessingfacility (Western New York Nuclear ServiceCenter) in West Valley, NY. These wastesrepresent millions of gallons of liquids andtens of thousands of cubic meters of solids; atINEL alone over 2200 m3 of unconsolidatedsolids remain.

Chemically and radiologically,reprocessed wastes are extremely complex.They contain fission products, residualactinides, cations from the dissolution of metalfuel rod containers, anions from acids used inthe dissolution process, alkali salts employedfor the purposes of neutralization, and avariety of organic sequestering agents. Toreduce their volumes and to stabilize theirchemistries, reprocessed commercial wastesin liquid form are often converted to solidform by drying and calcining them attemperatures below 600°C. During thecalcination step, the wastes decompose intoamorphous mixtures of chemically inertoxides; volatile reaction products are drivenoff. The solid products or calcines arecharacterized by moderate to high leachabilityand must be converted to chemically stableforms before they are disposed of.

Neither commercial nor defense high-levelwastes are uniform or well-characterized. Asa result, the development of waste forms thatare suitable for the immobilization of reproces-sed high-level calcines has continued to

challenge the waste managementcommunity. In response to thischallenge, researchers haveproposed a variety of wasteforms including noncrystalline,crystalline, and multiphasematerials. Each of thesematerials possesses uniquecapabilities and deficiencies.For example, noncrystallinewaste forms such as theborosilicate-based glasses arerelatively insensitive tofluctuations in waste streamcomposition, and the processused to prepare such materialsis reliable and straightforward.Industrial-scale processing ofborosilicate-based waste forms is in place andhas been demonstrated at the Defense WasteProcessing Facility (DWPF) at the SavannahRiver Defense Plant. However, borosilicate-based glasses are thermodynamically unstableand are susceptible to uncontrolledcrystallization under some repositoryconditions. Such materials lack the thermaland mechanical stability possessed bycrystalline waste forms.



Heather Hawkinsis a graduatestudent in theIntercollegeMaterials Re-search Programat the Pennsylva-nia State Univer-sity. She isstudying thestructure andstability of ac-tinide-doped NZPmaterials for theexperimentalportion of herPh.D. thesis. Hermentor is KirkVeirs of NMT-6

Ph.D. Thesis Explores Sodium Zirconium Phosphate(NZP) Waste Forms for Actinide Disposal (continued)

Unfortunately, operations at the DWPFhave been repeatedly delayed because of acombination of public relations issues andtechnical barriers. This delay has led torenewed interest in research on alternatewaste forms. Scientists in the waste manage-ment community have continued to propose,synthesize, and characterize novel wasteforms. Notable among these waste formsis sodium zirconium phosphate (NaZr2(PO4)3or NZP), a crystalline material that can accom-modate the chemical complexity of high-levelwastes.

The three-dimensional skeletal structureof NZP, as shown in Figure 4, allows theaccommodation of cations of various sizesand oxidation states on three distinct crystal-lographic sites; in fact, the NZP structure mayaccommodate all of the chemical species asso-ciated with reprocessed, commercial, high-level waste calcines. Uranium, thorium, neptu-nium, and plutonium occupy the zirconiumsite in the parent structure. Cesium andstrontium are accommodated on interstitialsites typically occupied by sodium. The substi-tution of sodium, zirconium, or phosphorousby fission products or actinides results in astructural isotype referred to as [NZP]. A widevariety of cations have been insertedinto the NZP structure. It may accommodateapproximately two-thirds of the ionic speciesof all known elements.

The [NZP] compounds permit theincorporation of all of the ions present inreprocessed, commercial, high-level wastecalcines into crystalline waste forms whoseresistance to dissolution and retention of[NZP] constituents is remarkable. Cursorystudies indicate that the [NZP] materials arehighly resistant to radiation damage. Ascrystalline waste forms, [NZP] compoundsoffer inherently low leach rates for singlephases, negligible coefficients of thermalexpansion, and the ability to immobilize highconcentrations of waste in high-density

phases. This latter characteristic of [NZP]waste forms renders these materials promisingcandidates for the disposal and consequentreduction of large volumes of wastes contain-ing significant quantities of nonradioactiveconstituents; plant operation, storage, anddisposal costs decrease with decreasing wastevolume. In this regard, crystalline waste forms,such as [NZP], offer a notable economicadvantage over the less dense borosilicate-based glasses.

The ease of processing [NZP] wasteforms is an additional feature that makesthese materials attractive alternatives to otherpotential waste forms, such as SYNROC(synthetic rock), a multiphase waste form. The[NZP] materials may be synthesized by solid-state reaction of mechanically-mixed, copreci-pitated, or hydrothermally prepared powders.Such [NZP] powders may be cold-pressed andsintered in air at moderate temperatures (600-1350°C); however, modifications of thesetechniques would be required for the indus-trial-scale production of [NZP] waste forms.

Some [NZP] compounds with wasteloadings as high as 40 wt % have beenprepared with simulated nonradioactive,reprocessed, high-level waste calcines by theauthor at The Pennsylvania State University;however, the preparation of [NZP] wasteforms with actual reprocessed high-levelwaste calcines has not been demonstrated.A methodology has been developed and testedthat allows one to determine appropriate batchformulations for several waste compositions.The batch formulations take into account siteand charge balance so that the final product isphase-pure, i.e., amorphous and undesiredphases are absent. Future work at LANL willinclude the preparation of actinide-loadedsamples, their characterization, and acomprehensive study of their behavior underrepository conditions.


Winter 1997

Publications,Presentations, and Reports(October 1996–December 1996)

Journal Publications

M. D. Diener, D. K. Veirs, and S. S. Eaton (Univ. ofDenver), “An Empty Fullerene Donor, C74,”submitted to J. Amer. Chem. Soc.

M. D. Diener, C. A. Smith, and D. K. Veirs,“Anaerobic Preparation and Solvent Free Separa-tion of Uranium Endohedral Metallofullerenes,”submitted to J. Chem. of Matr.

Conference Presentations

K. M. Axler and M. H. West, “Process Modelingand Development for Treatment of Uranium-Contaminated Solid Wastes,” The Second Interna-tional Symposium on Extraction and Processing forthe Treatment and Minimization of Wastes,Phoenix, AZ, October 27, 1996.

S. M. Dinehart, K. A. Qubat-Martin, D. W. Gray,V. A. Hatler, and S. W. Jones, “Radioactive SourceRecovery Program: Responses to Neutron SourceEmergencies,” Hazwaste World/Superfund XVII,Washington, D.C., October 15–17, 1996.

H. L. Nekimken, N. G. Pope, J. M. Macdonald,R. A. Bibeau, B. G. Gomez, D. J. Sellon, “Case Studyfor the Evaluation and Selection of Man-MachineInterface (MMI) Software,” Fall 1996 InstrumentSociety of America Meeting, Chicago, IL, October7–10, 1996.

The following were presented at The 1996 TrainingResources and Data Exchange (TRADE) Confer-ence, Anaheim, CA, November 19–21, 1996:M. A. Stroud, “Pollution Prevention and WasteManagement Performance Improvement at theLANL Plutonium Facility” and T. L. Binder,“Dressing Up With Somewhere To Go—Radiologi-cal II Practical Exercises at the LANL PlutoniumFacility.”

L. A. Avens, K. K. S. Pillay, and S. M. Dinehart,“The 94-1 Core Technology Research and Develop-ment Program,” The American Nuclear SocietyInternational Meeting, Washington, D.C., Novem-ber 11–15, 1996.

T. O. Nelson, D. E. Wedman, and H. E. Martinez, “Electrolytic Methods for theDecontamination of Metal Surfaces,” 23rd national Meeting of the Federation ofAnalytical Chemistry and Spectroscopy Societies (FACCS), Kansas City,Missouri, September 29–October 4, 1996.

The following were presented at the American Nuclear Society/EuropeanNuclear Society 1996 International Conference and Embedded Topical Meet-ings, Washington, D.C., November 10–15, 1996: H. T. Blair, K. M. Chidester,and K. B. Ramsey, “Fabrication of Mixed Oxide Fuel Using Plutonium fromDismantled Weapons”; K. M. Chidester, C. A. Beard, and H. T. Blair, “Fabrica-tion of Mixed-Oxide Nuclear Fuel in Support of the Parallex Project”; andK. B. Ramsey and K. M. Chidester, “Fabrication of Non-Fertile and Evolution-ary Mixed Oxide Fuels.”

H. T. Hawkins and B. E. Scheetz (Pennsylvania State University), “Preparationof Monophasic Sodium Zirconium Phosphate [NZP] Radiophases: PotentialHost Matrices for the Immobilization of Reprocessed Commercial High-LevelWastes,” Proceedings of the Materials Research Society 1996 Fall Meeting,Boston, MA, December 2–6, 1996.

E. Garcia, J. A. McNeese, V. R. Dole, and W. J. Griego, “Vacuum DistillationSeparation of Pyrochemical Residue Salts,” 16th Pyrochemical Workshop,St. Charles, Illinois, October 28–31, 1996.

C. A. Smith, M. D. Mayne, K. Rodriguez-Cales, J. C. Baiardo, and T. R. Mills,“Hydrochloric Acid Recycle: Chloride Crystallization and Acid Reconcen-tration by Gas Phase Membrane Separation,” 2nd Annual SERDP Symposium,Tyson’s Corner, VA, November 20–22, 1996.

M. A. Williamson, “The Chemistry of Fluid Fuel Nuclear Systems,” 16thAnnual Pyrochemical Workshop, St. Charles, IL, October 28–31, 1996.

Reports

F. N. Schonfeld and R. E. Tate, “The Thermal Expansion Behavior of UnalloyedPlutonium,” LA-13034, October 1996.

M. A. H. Reimus and J. E. Hinckley, “General Purpose Heat Source: Research &Development Program Radioisotope Thermoelectric Generator/Thin FragmentImpact Test,” LA-13220, November 1996.

D. D. Padilla, L. A. Worl, F. C. Prenger, and D. D. Hill, “Magnetic Roll Separa-tion of Sand, Slag, and Crucible,” Final Fiscal Year 1996 94-1 R&D ProjectReport LA-CP-96-262, November 1996.

K. W. Fife, C. W. Hoth, and J. B. Nielsen, “Nuclear Materials Stabilization andPackaging End-Of-Year Status Report,” LA-13238-MS, November 1996.


TA55


LosN A T I O N A L L A B O R A T O R Y

Alamos The Actinide Research Quarterly is publishedquarterly to highlight recent achievements and ongoingprograms of the Nuclear Materials Technology Division.We welcome your suggestions and contributions.

Nuclear Materials Technology DivisionMail Stop E500Los Alamos National LaboratoryLos Alamos, New Mexico 87545505/667-2556 FAX 505/667-7966

Los Alamos National Laboratory, an affirmative action/equal opportunity employer, is operated by the University of California for the U. S.Department of Energy under contract W-7405-ENG-36.All company names, logos, and products mentioned herein are trademarks of their respective companies. Reference to any specific company or product is not to be construed as an endorsementof said company or product by the Regents of the University of California, the United States Government, the U.S. Department of Energy, nor any of their employees. Los Alamos NationalLaboratory strongly supports academic freedom and a researcher's right to publish; therefore, as an institution, however, the Laboratory does not endorse the viewpoint of a publication orguarantee its technical correctness.

NewsMakers

Plutonium Futures The Science

Los Alamos, New Mexico 87545

Call for Papers

A formal Call for Papers has been issued for “PlutoniumFutures—The Science,” a conference to be held at the Hilton inSanta Fe, NM, on August 25–27, 1997. Authors are encour-aged to submit summaries of papers describing work that is

new, significant, and relevant to plutonium and actinide science. Topics include separations, transuranicwaste, isotopes/nuclear fuels, detection and analysis, materials science, novel plutonium/actinidecompounds and complexes, and environmental and biosphere chemistry. The conference programChairs must receive these summaries by March 24, 1997. The summaries will be printed in a confer-ence transactions document. The Call for Papers and other conference information is available byvisiting the World Wide Web at http://www.lanl.gov/PuConf97, sending e-mail to [email protected], orcalling 505-667-8663. The conference is sponsored by Los Alamos National Laboratory in cooperationwith the American Nuclear Society.

NMT Division welcomes a new scientific member. Dr. Dane Spearing recently graduated fromStanford University with a Ph.D. in geology and a minor in materials science. Much of Dane'sdoctoral research involved examination of the mechanisms and dynamics of displacive phasetransitions in a number of minerals and ceramics using nuclear magnetic resonancespectroscopy and x-ray diffraction. Dane will be working with John Huang (NMT-6) on thesynthesis and characterization of zircon as outlined in his postdoctoral research proposal.

As part of the NMT Division Review process, the following Extenal Advisory Committeemembers visited the division during this quarter to get familiarized with the division projects tobe reviewed in March 1997: Dr. Rohinton Bhada of the New Mexico State University (10/2/96),Dr. Gregory Choppin of the Florida State University (10/16/96), Dr. Robert Uhrig of theUniversity of Tennessee (10/16/96), Dr. Todd LaPorte of the University of California-Berkeley(11/21/96), and Dr. Darryl DesMarteau of Clemson University (12/17/96).

Professor Alexandra Navrotsky of Princeton University visited NMT Division on October 4 andpresented a seminar on "Thermodynamics of Glasses and Crystals Related to ActinidesImmobilization and Confinement."

LALP-97-5Director of NMT: Bruce MatthewsDeputy Director: Dana C. ChristensenChief Scientist: Kyu C. KimWriter/Editor: Ann MauzyDesign and Production: Susan L. Carlson

We would like to hear from our readers. If you have any comments, suggestions, or contributions, you may contactus by phone, by mail, or on e-mail ([email protected]). ARQ is now on the Web also. See this issue as well as backissues on-line (http://www.lanl.gov/Internal/organizations/divisions/NMT/nmtdo/AQarchive/AQindex/AQindex.html).

Documents

T 55A The Actinide Research Quarterly · seams on a soccer ball. Fullerenes and their discoverers, Richard E. Smalley, J. R. Heath, S. C. Scientists Study the Use of Fullerenes to