.

Approvedfm public release; distribution is unlimited.

TITLE:

AUTHOR(S):

SUBMITTED TO:

Los Alamos N A T I O N A L L A B O R A T O R Y

A LONG-PULSE SPALLATION SOURCE AT LOS ALAMOS: FACILITY DESCRIPTION AND PRELIMINARY NEUTRONIC PERFORMANCE FOR COLD NEUTRONS

G.J. Russell, Lansce-12 D.J. Weinacht, Lansce-DO E.J. Pitcher, APT-TPO P.D. Ferguson, Lansce-12

0 -4 0

Proceedings of the "Symposium on Materials for Spallation Neutron Sources 1997," held at Orlando, Florida, February 9-13,1997.

n

Los Aiamos National Laboratory, an affirmative actionlequai opportunity employer, is operated by the University of California for the U.S. Department of Energy under contract W-7405-ENG-36. By acceptance of this article, the publisher recognizes that the U.S. Government retains a nonexclusive, royalty-free license to publish or reproduce the published form of this contribution, or to allow others to do so, for U.S. Government purposes. The Los Aiamos National Laboratory requests that the publisher identify this article as work performed under the auspices of the U.S. Department of Energy. The Los Alamos National Laboratory strongly supports academic freedom and a researchel's right to publish; as an institution, however, the Laboratory does not endorse the viewpolnt of a publication or guarantee its technical correctness.

Form No. 836 R5 ST2629 lag1

DISCLAIMER

This report was prepared as an account of work sponsored by an agency of the United States Government Neither the United States Government nor any agency thereof, nor any of their employm, makes any warranty. express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or use- fulness of any information, apparatus, product. or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any spe- cific commercial product, process, or service by trade name, trademark, manufac- turer, or otherwise does not necessarily constitute or imply its endorsement, r e a m - menduion, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

A Long.Pulsc Spallation Source at Lor A h x m FacUlty Descrlptlon and PrcUmlnary Neutrodc Pvlormpna for Cold Neutrons

0. J. Russell, D. J. Wcinacht, B. J. Pitchex, and P. D. Puguson Los Alamos National Iaboratory

Los Alamos, NM 87545

Abstract

The Los Alamos National Laboratory has discussed installing a new 1- MW spallation neutron target station in existing building at the end of its 800-MeV proton liaear accelerator. Bccawa the accelerator provides pulses of protons each about I msec in duration, the new s o m would be a bng-Pulse Spauatlon S o w (LPSS). The facility would employ vertical wrtraction of moderatorr and mficctom, and horizontal wrtraction of the spaUation An LPSS uses coupled moduatorr rathe than dacoupled om. 'Ihue am pottntlal gains of about a factor of 6 to 7 in the timMwaged neutron brightness for cold-neutron production from a coupled liquid IL modaator compand to a decoupled one. Howevu, these gains come at the urpease of putting "tails" on the neutron pulses. The particulars of the neutmn pulses fmm a modetatar (e.g., energy; depeadent rise times, peak inWties, pulse widths. aad decay constant@) of the tails) am crucial paramtas for dcdgnhg htmmmts and

materiat Inand-718 is the m h c e target canista and proton beam W o w mtaial, with Al-6061 being the choice for the liquid I& moduator canistm and vacuum containex. A 1-MW LPSS would haw wodd-class neutmnic patormaace. We describe the proposed Los

timavaaged neutronic peaformaace of a liquid HZ moderator at the 1- MW LPSS is equivalent to about 114th the calculated neutronic pertormaace of the best liquid Dz moderator at the Institut Lauchngcvin nactor. We show that the timGavaaged modaator neutronic brightness incnases as the size of the moderator gets smaller.

esbimatingthdfpatonnMceatanLPSS. ~ i s o w m f ~ c e q

Alamos Ipss facility, and show that, for cold neutrons, the calculated

The Lor Alamos National Laboratory has discussed (1) installing a new I-MW spallation neutron target station in an existing building at the ead of its 8OO-MeV proton linear accelerator (2). Because the d e r a t o r provides pulses of protons each about I msec in duration, the new some would be a Long-Puke Spallation S o m (IPSS), as compand to a Short- pulse Spallation S o w (SPSS) which has proton pulsc widths of around

spallation source would be housed arc located at the Los Alamos Neutron Science Center (LANSCE) (9). Because the spallation s o w would use existing LANSCE infrastructuzc and facilities. such an LPSS facility would be extremely cost effective. Since no new accelerator is to be built or commissioned, p m t estimates arc that the LPSS could be designed and built in three years (1).

The target system (targets. moduators, poisons, decouplus. liners, and nflectors) is the part of a target station that contributes dinctly to the production of useful neutrons. (For most users of a pulsed spallation- neutron mum, useful neutrons can be defined as those hcaded in the right direction with appropriate energy at the right time.) A target station consists of the target system, bulk shield, nmote handling system, and

1 Or less (3-8). The acoelerator and tbe bullding in which the

ancihy equipment. The paarculars of a target station depend on

Target stations am vital componeneS of a spallation-neutron source, and targetaation Wgn plays a Wor role in detumfning the ovcrall (neutronic and opedonel) paformaact of the facility. SeVetat new concepts am bdng put f o d to meet the chatlmge of designing a target station tor the next genedon rpauation neutron som (1-5 MW of proton beampowa). It is generally believed that a target station designed for 1 MW can employ &sting target technology (e.g., solid targets cooled by dtha light or heavy watu) (10-12); for higher proton beam powas such as 5 MW, liquid mercury tagets am presently being studied (13.14).

whether it is designed fOf 811 SPSs Of M DsS.

The main advantage of an LPSS for neutron rca#aing will be for WCperIments requiring long-waveleagth ("cold") neutrons or cxpuimmts for which good wavdength nsolution is not needed. For many such wrpaiments, the LPSS will pat ormas wen as or better than the pnsent world leader, the 60-MW nuclear reactor at the M t u t I~wIangevin (ILL) in -le, Rance(15). BccausctheIPSS will produce apnlstd neutron kam ratha than a continuous rtream of neutrons like that provided by a nuclear reactor, the LPSS will use timwf-flight methods for many neutron rcattaiag utperimenb and will open up new opptunities for advances in neutron rcattuing mthods.

The basic neutronia of an LPSS and coupled moderators have becn discussed in Refs. 1619. We will now describe the physical concept of

pufonnance of rmfennce target system to that of the ILL for cold neutron production.

LPSS at LANscE, and cornpan the timaveraged neutronic

Rgun 1 shows the experimental anap at the end of the LANSCE acceluator. Thw anas include the Manuel Lujan Jr. Neutron Scattering Centa W S C , which is now bdng m f d to as the Lujan Center), the Weapons Neutron Research (WNR) facility, and the building housing the proton Storage Ring (PSR), and Area A. The new LPSS will be located in Area A of the LANSCE complex. This new neutron source will provide complemntary capabiitia to thost already available at the Lujan Center and the Weapons Neutron Research (WNR) facility. It will not affect operations at these facilities. The combination of the existing

versatile sources of neutrons in an e n q y range covwing fifteen orders of magnitude: from hundnds of nanovolts to hundnds of megavolts. For many neutron scattUiag experiments using cold neutrons, the LPSS will provide capabilities comparable to those of the ILL 60-Mw reactor.

facilities and the 1-MW LPSS will provide uniquely pow- and

pigun 1: Adal view of LANSCEaccelaatot and experimatalareas. -Ais when the proposed LPSS will be built. This area and the accelantor were f d y known as the Los Alamos Meson Physics Facility 0. -

As mentioned above, the LPSS neutron ptoauction target will be located in Ana A (see fig. 1) which origlaallr housed nuclear physics instruments. Most of tbcsc inshumcnts eithw have been moved or will be decommissioned in the futun because the facility will not be funded as a nuclcar physics facility in the futun. ?he Area A building constructed of metal beams with a sheet metal skin, has approximately 3,000 m* of floor space and a usable height within the building of about 14 m. A 2.5-m- thick conmte floor would support the massive biological shielding in the center of the building. No modifications to the building or the floor will be rcquhd for the IPSS.

The facility is quipped with utilities and ancillary systems including:

- two 30-0311 radiocontrolled bridge cranes that can be coupled for 6O-ton lifts;

a 19,oooCfm capacity radioactive air handling system with a high efficiacy particulate air -A) filter bank and an approved stack emissions monitoring system;

20,000 tons of iron and conmte for biological shielding, some of which can be utilized for the IPSS;

three 3-h4W capacity cooling water systems that me adequate for IPSS;

a 13.2-kV electrical rubstadon with fifteen 1ooO-kVA distribution transformen (nccntly mfurbiished) that can provide power for experiments; and

three nmote handling manipulators and their control systems that will be used to handle targets and other radioactive components.

These systems. which constitute a considmble infrasmctural investment (approximately S38M). will be used to the fullest extent possible to support the LPSS. shielding will be reused when possible to d u c e cost and minimkc the volume of hazardous waste that must be traaspatted away from the site.

including the flight paths. A monolithic steel and conemto biological shield consisting of about 4.5 m of steel and about 1.5 m of c o n a t e will occupy the central part of A m A. Thc top of the shield will be about 7.0 m from the floor. A 1 .S-m-thick poured conemto wall will comprise the outer wall of the shield. This wall will provide seismic stability, a banicr for lowcncrgy neutrons, and containment for radioactive air produced by secondary particles from the target. The shield is designed to limit the radiation dose at the M o r boundary of the monolith to 0.1 mnmh

FQurC 2 show the ovetall floor plan of the LPSS cxplxbatal ana,

The neutron production target and moderators will be located at the center of the monolith with 15 beam tuba arranged radially. A hot cell will be adjacent to the shielding monolith directly downsttwm of the target system as shown in the cut-away drawing in Fig. 3. Moduators will be extracted vertically from the target chamber and drawn into a remotely operable shielded cask that can be m o d on rails to a position above the hot cell. "be modemtom can be l o d into the hot cell for servicing. This came cask will service the beam diagnostics and materials test components located ups- of the spallation target. The spallation targets will be wrtracted hoazOntally from the target chamber and drawn into the hot cell for ruvidng. This approach ensures that the most highly activated component in the system (Le., the spallation target) wil l always be shielded and contained. Handling of the spallation target will be conducted completely sqaratc from neutron beam expaimmts, thus providing unimpeded usa access to expcdmats and isoladon of radioactive targets and moderators in a controllable mmm. operations in the hot cell will be performed with remote handling systems.

Thc hart of the new LPSS is a system of opauation targets and moderators that generate neutrons for numKous nseatch applications. Loe Alamos National Laboratory has considerable cxpaiam with both the opuatlon of @lation target systems and with the design and opdmirabion of advanced target systems for a variety of applications including the Lujan Center ( 3 9 , WNR e), and the Acoelcrotor Production of fitium (APT) project (20). In our ref- target- moderator design, the spallation target is split to produce the "fiux-mp" goomtry (21) used s u d y at the Lujan center. Figure 4 chows the LPSS rcfennce target-modaatot geawtry which is composed of a split target, two liquid hydrogen moderators in wing gwme4y. and a liquid h y d r o p ntoderatot in flux-trap geometry (viewed both in tMsmission geomtry from one side and in backscattuing geomhy from the opposite side). We mport hue only neutronic performance data for liquid I& moderators. Ambient-- moderators are also unda mdy and may be of intextst for an LPSS. The actual target-modmtor configumtions and moderator typw used will be detcdned by fume neutronic optimization studies and the suite of spectrometers to be installed at the IPSS facility.

A reflector (e.g.. C, Be, W, Pb, etc.) will surround the spallation targets and moderators to enhance the neutronic putormance of the modesators. The nflector must be carefully designed to help produce neutron pulse shapes from the moderators that are suitable for scattering experiments. A composite neutron reflector (composed of beryllium and lead) is also being consided for the LPSS reflector (16-19.21). Heavy water wil l be used to cool the reflector and the spallation targets.

The neutron production target and its associated moderators, reflectors, and iron shielding will occupy a 2-mdiamcter stainless steel vacuum vessel at the center of the shielding monolith. Because the radiation and

heat deposition levels in the vacuum chamber will be low, this component should cuvc throughout the lifetime of the facility

A moderator is bdng considad for Ultra-Cold Neutron CUCN) production. Ultra-Cbld Neutrons (22) ut neutrons with &es less than about 10.' CV. AS rcoping studies of this specialized moderator are currently in progtess, its integration into the LPSS will be part of the LPSS moderator system concepts going forward.

In the refennce LPSS target-moderator geometry, neutron beams will be extracted from both sides of each wing moderator and the dux-trap moderator will be viewed in both transmission and backscattering geomtry, providing six moderator viewed nufaces each with a 10 cm by 10 cm fieldof-view. Since engInaering detail is known to significantly influence target performance, a considerable amount of such detail has been included in the Monte Carlo simulations of the target system. For example, the pnsent Monte Carlo model accounts for targethflector dilution by an amount of heavy water coolant that is adequate for 1 h4W of incident beam pow on the target, a proton beam window. target enclosures, moderator canisters, moderator vacuum enclosures, and neutron flight path penehations. The model does not account for target and moderator cooling lines and baWes or s ~ c t u r a l material in the reflector.

The LPSS flight paths will be quipped with chambers for neutron choppers that will also serve as guides for bladGtypc beam shu#ers. Most of the neutron cca#uing sptmmeters at the LPSS will require what is called aTo choppet that will protect a spectrometer from the flash of fast neutrons and gamrna rays that is gamtcd when pmtons strike the tungsten neutron production target(s). Some IPSS spcctromters will

masunment frame or to shorten the neutron pulses produced by the target system. The location and design of these choppas will depend on the spectrometer wcd, so the chopper housing will be designed to pamit positioning flexibfity and to allow d y access to choppers for maintenauce purposes. Additional rtsearch and development will be necded to ensun that the choppas function nliably and can be maintained without excessive impact on LPSS opmtions.

rlso need lightweight disk choppas either to define the timcof-flight

As mntioned pwiously. useful neutrons (at a pulsul spallation neutron source) arc those neutrons headed in the right dirsction with the rpptopiiate magy at the comct time. Unfortunately, spallation neutrons produced diradly by the rpauation target rarely have these d e s i characteristics. We must, thmfore, add the ~ecessary systems and devices to a ban neutron spallation target to tailor the neutron pulses so their charactexistics axe ps close as possible to the Usezs requirements. As mentioned above, a complete spallation target system consists not only of spallation target(s), but also moduators, retkcto~(s). and, in the case of an SPSS, poisons, &couplers, and liners.

In addition to the choice of material. temperature, geometry (e.g., wing versus flux-trap moderaton) (21), and the pnscnce or absence of a reflector. moderator neutronic performance is also strongly tied to the pnsence or absence of poisons, dacouplers, and liners. The choice of mate&& and thickness for these target system components is a crucial part of moderator design (10). The function of poisons, decouplers, and liners is to tailor the temporal and energy characteristics of the neutron pulses emitted by the moderator (17). Figwe Sa shows the arrangement of poisons, &couplers and liners for a split-target, flux-trap moderator gaometry (3.4). For t h d neutrons, the poison neutronically defines that part of the moderator "viewed" by M experiment. Dccouplers surround a moderator and both geometrically and neutronically isohte it

Rgurc 2 Overall layout of the LPSS facility. The target system and shielding monolith will be positioned in Ana A as shown. The target test cell is no longer bcing consi&mi for the UPSS.

figure 3: Cut-away view of the shielding monolith and hot cell.

W g u n 4 U S S reference target system. This figure docs not show the reflector, UCN moderator, or bwm tubes.

FULLY MCOUCLSO 1.00 RELATIVE NEUTRON FLUX (s I mV)

[*I.. OYOTEY Y L N W I 00 (10 PULIE WIDTH. OTANDARD DEVIATION (E I MOW

FLUX-TRAP DECOUCLER REFLECTOR DEOOUPLER

niuomED

FULLY WUPLED OYOTEY

led.

Figun 5: Arrangement of poisons. decouplers, and liners in a flux-trap modemtor geometty. As &own in Fig. (a), poisons an t yp idy oriented parallel to and positioned come distance (-1 to 3 cm) behind the modaator viewed surfaces. The flux-trap demuplus neutronidy insulate modercltors from one ~ 0 t h ~ . wheseas the nflector decouplac neutronidly isolate moderatonr from the adjoining nflector material. &ers mtronically bulate the nfiector from the moderatot viewed surface. PigUte (b) shows the effect of poisons, dtcouplers and liners on neutron pulse intensity and pulse width far liquid H2 (orthdpara W50 v9b) moderators. The labels on the left ride of the bar graph indicate what items amplesent for the comsponding bm. The neutron pulse width is defined as the standard &viation of the time at which neutrons leak from the modaator viewed nuface. The 22.5-a-long, D2o-coOled W tod-target is singly split and the four 5x13~13 cm3 modmators an in flux-trap geometry. The poison is 0.00508-cm-thick 04 and the decouplers and linac an 0.0813cm-tbkk Cd. The nflector is D20-cooled Be @2O/Be 15/85 a). The proton beam ene%y is 800 MeV. The target-moderator geometty is that described in Ref. 3.

from the nflector. Ihs geomctddy and neutronidly isolate the "viewed" d a c e of the moderator from the reflector. We deliberately &!he decouplus and b a s separately because they caa be m m t materials each with distinct thickness, as in the bjan Center target rystem design 0.4).

The goal of SPSS moderator deslgn is to get as much useful neutron intensity from a moderator as possibk with little or no attadant degradation in the neutron-pulse time distributions. For LPSS moduator design, poisons, decouplers, and liners will dthcr be not used or used judiciously. The goal of LPSS modaator design fr to get as much wfid neutrw intensity h m a moderator as possible while matching the neutron-pulse time dis~butiOnS to wrperimntal q-ts (la). We will now discuss the neutronic gains in going from and an SPSS to an LPSS (19).

If we employ decouplers and liners in conjunction with a moderatot cumundcd by a reflector, wc refer to those modaators as "dacoupled" modantors. To date, only decoupled moderators have been used at the

of UI upgrade project to the bjan facility (23). The choice of material and tbidmess of the mataial for decouplere and liners is impoltant in optimizing the neutronic p c d o m c e of the next generation (1-5 MW) SPSS. Adequately cooling the decouplers and liners for the next generation SPSS's will be a design challenge.

If wc do not employ decouplers and liners in conjunction with a moduatot surrounded by a nflwtor, wc refer to those moderators as "coupled" moderators. Coupled moderators an in use at the SINQ quasi- continuous spallation neutron s o w (24). and, as mentioned above, partially coupled moderators an being designed for an upgrade to the Lujan Cenm spallation taget system. Coupled moduators am provide dgnificaatly highu neutron fluxes than decoupled ones. Howevu, neutron pulse widths Erom a coupled moderator an much larger than that from I decoupled one. We illustrate this neutronic gain in Rgurc 5b for a liquid H2 moderator as the decouplers and liners an removed in stag=

Uristhg SPSS tacilith (3-8). HOWeVa, f b h j M h& will be wing pattially coupled moderatorr in its new SPSS target rystetem which is part

(Le., in going from a decorapled moderator to a coupled moderator). For a liquid hydrogar modantor, a totally coupled moderator provides about 6 to 7 times grw& neutron pulse intensity (for E 5 mew than a decoupled moderator. Howeves, as indicated by the standard deviation, the neutron pulses an "broadd' in time from a coupled moderator comparsd to a dtcouplad one, which is an issue that must be dealt with effectively. These gains in going from decoupled to coupled moderators depend on the t a r g e t - m r geomrry.

pigun 6 depicts the enugy-dependent gain in neutron bwm intensity for a coupled liquid I-& moderatot compand to a dacoupled one. As caa be teen, the maximum gain in neutron intensity occurs below the dacoupling umgy (in the "useful" neutron @me). ThC time distributions of coupled and decoupled liquid & moderatonr uc depicted in Fig. 7. Coupled modc&m bave higher peak neutron leakage intensity than decoupled om. Howeva; coupled moderators have a longer ''tail" on the neutron pulses.

In Fig. 8, wc &OW the ratio of c o u p l d ~ ~ p l e d data for liquid Hz moderators integrated over dm, wc call this rhe Hme-dcpcndcnr neutron leakage gafn. The resulk chow that the neutron gain depends on the time

gain for liquid EL is the factor of between 6 and 7 (as r +). In practice, the actual Hme-drpendenr neutron kakage gain will depend on the "c@ucring realities" of the specific target system being considered.

The data pnscnted in Figux~~ 5-8 an for the nux-trap moderator geometry of Ref. 3. and there an no pmmoderators in the calculations. Also, the 5x13~13 cm moderators an unpoisioned, and the B W reflector is 85/50 v9b B-0.

O W Which the nCUmIU CllIl be Utilized in M CXpClimCDt. The IlUXhUIXl

The nfcrence geometry for Monte Carlo simulations of neutronic p c d o m c e is a singly-split tungsten target with a square cross section. This geomettical model was devised by Pitcher (17). The Monte Carlo model is based on horizontal proton beam insertion into the taget system The Monte Carlo geometry of the mference target system is depicted in Fig. 9. The upstream target is 10~10~8.5 cm' and the downstream target

is 1OxlOx19.5 cm3, with homogenized mataial compositions equivalent to that of the tungsten plate target concept pposcd by carpentet (7).

1 MW of proton beam power at 2 &V. We i n d the coolant gap to 0.2 cm and rdded 0.05 cm of tantalum cladding to each plate pa a discussion with Broom (25). TWs gave the following homogwizbd volume fractions of 69.4 v% W, 9.4 v% Ta, and 21.2 v% Dzo for the ups- taget and 85.1 v% W, 4.6 v% Ta, and 10.3 v% Dzo for the downstnam taget. Inconel-718 target canisters. The flux-trap gap between the two target sections is 115 cm.

Thematerialcomposidom of the two targets were O ~ y ~ t o h M d l C

Both UL'@ & O ~ S are enclosbd in 0.2~m-thick

Located at the flux-trap gap is a 6x10~10 cm3 liquid IL flux-trap moderator. The liquid hydrogen modemtor is enclosed in UI A-6061 canister with 0.35 cm walls at 20 K. The moderator canister is separated from a 0.35-m-thick AI-6061 vacuum canister by a vacuum gap of 0.5

modaators on the top and bottom of the upstnam target. The flux-trap moderator has wrapped around its perimeter, a 2-m-thick layex of Hzo, at a tempcratum of 293 K. A similar Ha layer is pmcnt around each wing modCmtor, except that the thickness is 1 cm. For the flux-trap moderator, the distance l b m the proton beam centeriine to the inner surface of the liquid IL is 7.1 cm. This distance for a wing moduator is 8.4 cm. The refaace arthdpara-hydtogea concentration was assumed to be 50150 v% at 20 K. The anticipated orthdpara-hydrogen concentration in the LPSS moderator needs furtha study.

CIIL A Dimilar Canister m - t d k for the two liquid-& wing

Before striking the spallation targcts, the 800-MeV proton beam passes through a proton beam window, nprestntbd by two 0.108cm-thick Inconncl-718 plates separated by a 0.2-m-thick gap filled with Hzo.

The overall nflector size is 150 cm diametu by 150 cm high. Thh reflectMcomposition was assumed to be B W w i t h 85 v% Be and 15 v% D20. Pitcher (26) has &own that the neutronic performance of coupled lmodaators is not too sensitive to the Dzo coolant &action in a tungsten target. A similar study needs to be performed for the coolant -on in the nflector.

&s.ub

We used the WIET Codc System (LCS) (27) to calculate the tim amaged paformance of the LPSS refennce target system. The magnitude of the abe%y-depcndent, spatial-amge. modaator brightness is Wvcd tiom point dctector tallies placed 10 m from the moderator leakage nufacu. The four leakage surfaces from the wing moderators were a m @ togethu to nduce the statistical mor. The results of the calculation are shown in Rg. 10 for the nfurnce target system Also, wc am studying ways to improve the IPSS modaatot performance below about six angstroms. An example of this effort is depicted in Hgure 11, where wc change the moderator width and height (the moderator thicknesses are the same) from 10 cm by 10 cm to 9 cm by 9 cm. Figure12 shows data for 8 cm by 8 cm moderatom. Basad on these calculations, the overaU SOW brightness of the LPSS r e f m c e targct system (from 2-10 A) is comparable to about one quarter that of the ILL over the wavelength range. two to ten angstroms.

It is important to note that all thtac moderators in our refmnce targct system an high-intcnsity moderators (Le., all moderators perform essentially the same neutronically). Thus, for the target-moderator geometry of Figure 4, all eighteen neutron beam lines (e.g.. thne beam lines per moderator viewed surface) would be serviced with high-intensity cold neutron beams.

Tungsten is our reference material for the LPSS spallation target. It is a high tempcram material with good characteristics for producing

0.0001 0.001 0.01 0.1 10

NEUTRON ENERQY (#VI

pigun 6 Neutron flux spsctrum for a daooupled liquid H2 (orthdpara 5W50 v%) moderator showing the eaugy-dependent dif€aenca of leakage neutfons.

1.4

1 1

1 A

0.8

0.m

0.4

0 1

.n

F 5 p 7: Tim distributions for coupled and dacoupled liquid H2

timedependent differences of leakage. neutrons. ( o r t h d m 5W50 v46) moda&S in flux-trap gtomctry, showing the

0.001 0.04 0.1 4

TUE (nil 40 4 0 0

Figure 8: The timedependent coupledldecoupled gain for an coupled and decoupled liquid HZ (orthdpara 5W50 6) moderators in flux-trap geometry, showing the time-dependent differences of leakage neutrons.

.

Rgurc 9 Csoss sectional views of the LPSS target system Monte cario model: (a) elevation view showing the split target, flux-trap gap, and the two wing moderators; (b) plan view depicting the flux-trap moderator and neutron bcam extraction in backscattenn ' g geometry and transmission geometry; (c) plan view of upper wing moderator showing neutron bcam extraction; and (d) plan view of lower wing moderator depicting neutron beam extraction. A total of six moderator viewed-surfaces are possible with this target-moderator configuration.

. spallation neutrons. However, tungsten is a modcrate neutron a b s o k requiring special attention to design details, including target geometry and the choice of coolant. Cladding tungsten appears to be required for high-power spauation target applications because of potential corrosion issues. Tungsten has been used su:ucctssfully at the Lujan Center as a spallation target material. Because of its successful use at the LANSCE 800-MeV proton acceluator, Iawnel-718 is the choice for the r e f m c e target canister and proton beam window material. Aluminum-6061 is the refmce matcrial for the liquid IL moderator canister and vacuum contain% this material has been used for this purpose at the Lujan Center and at othw spallation neutron s o w . More work needs to be done on the choice of these materials for the IPSS application. As experience from operating spallation s o w accumulates, as appropriate data from the APT materials irradiation and corrosion programs become available (29.30). and as our basic understanding of radiation damage to materials in a spallation source environment improves, we need to reevaluate our choices of materials for the IPSS application.

10"

10"

pigun 10 Avuagc moderator brightness for the reference target system as a function of neutron wavelength. The 10 cm by 10 cm wing moderaton and the 10 cm by 10 cm flux-trap modaator (viewed in both backscattering geometry and transmission geometry) all provide high- intensity neutron beams for cxperimeng.

I lo" 11 8L lo" p! a

1 0'0 2 3 4 5 8 7 8 9 1 0

Neutron wavelength (A)

Figun 11: Average moderator brightness for 9 cm by 9 cm wing moderators and 9 cm by 9 cm flux-trap moderator (viewed in both backscattering geometry and transmission geometq). The moderator brightness increase as the moderator size gets smaller.

1

Agure 1 2 Avttage moderator brightness for 8 cm by 8 cm wing moderators and 8 cm by 8 cm flux-trap moderator (viewed in both backscattcnn g geometry and transmission geometry). The moderator brightness inutasc as the moderator size gets smaller.

The performance of a r e f m c e target system for the IPSS has been established using the WS. W e ongoing rtsearch and development is

system demonstrates that adequate neutronic performance for cold neutrons can be obtained. Work is continuing on the neutronic optimization of an LPSS target system, including calculating time- dependent neutron beam fluxes. The coolant fractions in the various components of the target system need furthw ctudy.

The per fomce of IPSS for neutron scattering depends on both the time-integrated neutron flux generated by the target system and on the shape of the neutron pulses. These two quantities may be traded against one another by altaing the relative amount8 of reflector materials rumunding the target-- system. A nscafch and development program that accounts for spectrometer perfomce will be needed before final decisions uc made regarding the optimum configuration and materials for the LPSS target system.

Radiation damage to materials and corrosion issues wil l likely determine the lifetime of critical componeats in the IPSS spallation target system, including the proton beam window. We must continue to evaluate the choice of mataials for the LPSS application as: a) data from radiation damage and corrosion experimntS become available; b) our basic theoretical understanding of radiation damage and corrosion effects inaease; and c) experience is gained from operating existing SPSS's.

A 1-Mw LPSS has worldclass neutronic performance. For cold neutrons. the calculated timeaveraged neutron performance of a liquid H2 moderator at the 1-Mw IPSS is equivalent to about 114th the calculated perfomawe of the best liquid Dz moderator at the IUL reactor. The IPSS moderator brightness incrurses with decreasing moderator size. All the neutron beams from the reference LPSS target system en high- intensity neutron beams.

likely to lead to e m better pc€formanccl the reference LPSS target

Acknowledeements This work was supported by the Department of Energy. BES-DW under contract No. W-7405-Eng-36.

Refcnnces 1. "A Long-Pulse Spallation Source at Los Alamos National

Laboratory", (Report LA-UR-95-2760, Los Alamos, National Laboratory, October 1995).

2. M. S. Livingston, "LAMPF a Nuclear Research Facility" (Report LA-6878-MS. UC-28 and UC-34, Los Alamos Scientific Laboratory, Septemba 1977).

G. J. Russell, C. D. Bowman, E. R. whitalru. H. Robinson, and M. M. Meier, "LANSCE High-Power (200 FA) Target-Moderator-

Meeting of the International Collaboration on Advanced Neutron S o m . Rutherford-Appleton Laboratory report RAL85-110 (November 1985), pp. 272-293.

3.

Reflector-Shield," in ICANS-VIII: Promedm * gs of the Eighth

4. 0. J. Russell, J. S. oilmore. H. Robinson, 0. L Legate, A. Bridge, R. J. Sanchez, R. J. Bnwton, R. Woods, and H. G. Hughes, W S C E Target System Performance," in Advanced Neutron Sources 1988: Proceedings of the Tenth MCCting of the International Collabomtion on Advanced Neutron Sources

England), Vol. 97, pp. 4834% (August 1989).

0. J. Russell, H. Robinson, and H. 0. Hughes, 'The LANSCE Target system," in Proceedings of the Internatiod Workshop on Cold Neuttvn Sources, Los Alamos National Laboratory report LA-

N. Watanabh S. Ikeda, and Y. W w a , "KENS Target Station, :' in IG4hS-W: Proceedings of the Fourth MCCting of the International Colhbomtion on Advanced Neutron Sources, Y. Ishikawa, N. Watanabe, Y. Endoh, N. Niiura, and J. Newsam, Eds., National Labomtory for High Enu'gy physics npoa KENS-II

(1CANS-X), W Hw, Ed. (IOP Publishing Ud., Bristol

5.

1214642, PP. 565-573 (August 1991).

6.

(March 1981). pp. 181-199.

7. J. M. Carpen6z. C. W. Potts, and 0. H. Lander, "Intense Pulsed Neutron Sonrce (JPNS) a! Argonne National Laboratory (ANL): A Status Report as of June 198V h ICANS-VI: Proceedings of the Sixth Meethg of the International Collabomtion on Advanced Neuttvn Sources, Argonne National Laboratory report -82-80 (January 1983). pp. 77-101.

8. A. D. Taylor, "SNS Moderator Pwformancc," in ICANS-VIII: Roobedings of the Eighth Meeting of the International Collaboration on Advanced Neutron Sources, Rutherford-Appleton Laboratory q r t RAL-85-110 (November 1985), pp. 319-328.

P. W. Usowski, C. D. Bowman, G. J. Russell, and S. A. Wcnder, 'The Los Alamos National Laboratory Spallation Neutron Sources,"

9.

NUCL Sci. and En@., 106, pp 208-218 (1990).

10. N. Bultman, A. Jason, E. Pitcher, 0. Russell, W. Sommer, D. Weinacht, and R. Woods, 'Zos Alamos Nwrt-Oeneration Spallation Sotme," (Report LA-UR-954300 Volume I, Los Alamos National Laboratory, December 1995).

11. "PNS Upgrade A Feasibility Study", (Report ANL95/13, Argonne National Laboratory, April 1995).

12. B. Guttek, "Resent Status of the ESS Tantalum Target," in ICANS- HII: Proceedings of the 13th Meeting of the International Collaboration on Advanced Neutron Sources, G. S. Bauer and R. Bercher, Eds., Paul S c h m Institut report PSI 95-02, ISSN 1019- 6447, pp. 495-509 (November 1995).

13. 0. S. Bauer, 'Mercuy as a Target Material for Pulsed (past) Spallation Neutron Source System," in ICANS-XIII: Rocacdings of the lWrtccnth Meeting of the International Collaboration on Advanced Neutron Sources, Paul S c h m Institut Roceedings 95- 02 (November 1999, pp. 547-558.

14. T. A. Gabriel, et al, 'y)vcrview of the NSNS Target station," in proooedings of the Intcmational Topical Meeting on Advanced Reactor Safety, ARS'97, Orlando, Florida (1997).

15. P. Aguon, "Special Neutron Sources," in Symposium on Neutron Scattering in the Nineties, Jan. 1418,1985, IAEA Vienna (1985).

16. G. J. Russell. E. J. Pitcher, and P. D. Perpuson, "Neutronic

Workshop on Neutron Instrumentation for a Long-Pulse Spallation Source, Lawrence Bcrkley Laboratory report, LBL-37880, April 18-

Performance of a Benchnuuk 1-MW, LPSS," Pmcecdm - gs of the

21,1995, pp. m-33 to IU-41 (April 1995).

17. 0. J. Russell, E. J. Pitcher, and P. D. Ferguson, 'y=Oupled Moderator Neutronics", in 1WS-XlI: Proceedings of the 13th Meeting of the International Collabomtion on Advanced Neutron Sources, 0. S. Bauer and R. Berchcr, Eds., Paul Schecnr Institut report PSI 95- 02, ISSN 1019-6447, pp. 495-509 ( N O V C ~ 1995).

18. E. J. Pitcher, 0. J. Russell, P. A. Seeger, and P. D. krguson, "Performance of Long-Pulse Source Reference Target-Moderator- Reflector Configurations," in ICANS-XII: Proceedings of the I3th h k t i n g of the International Cohkbonation on Advanced Neutron Sources, 0. S. Bauer and R. Berchet, Eds., Paul Scherrer Institut report PSI 95-02, ISSN 1019-6447, pp. 323-329 (November 1995).

19. G. J. Russell, E. J. Pitcher, P. D. Pcrguson, and B. W. Patton, 'Zong-Pulse Spallation Source Neutronic Perfomcc," Workshop On Neutron Scattcrhg Oppoaunities At Long Pulse Spallation Sources, 24-27, June 19%, HMI Bulin, Germany (to be published).

20. E.J. Pitcher, G.J. Russell, R.B. Kidman, P.D. Pcrguson, and M. Todosow, "Neutronic Design of the APT TargetlBhket," to be published in the proceedings of the Embedded Topical Meeting on "Nuclear Applications of Accclcrator Technologies, 1997.

21. G. J. RUSSCU, P. D. Puguson, E. J. Pitcher, and J. D. Court, ''Split- Target Neutronics and the MLNSC Spallation Target System," CP392, Applications of Accclcrators in Research and Industry, edited by J. L Duggan and L L Morgan, AP Pnss, New York

22. Golub, D. Richardson, S. K. Lamorcqux, --Cold Neufmns. (Bristol, England, Adam Hilger imprint by IOP Publishing Ltd, 1991).

1997, pp. 361-364.

23. P. D. Pcrpuson, G. J. Russell, E. J. Pitcher, and J. D. Court, "Calculated Neutronic Performance for the Upgraded Manuel, Lujan, Jr., Neutron Scattering Center Target System," - this TMS meeting

24. W. E. Wscher, "Status Report of SINQ: A Continuous Spallation Neutron Source," in Advanced Neutron Sources 1988: Proceedings of the Tenth Meeting of the International Collaboration on Advanced Neutron Sources (ICANS-X), Dianne Hyer, Ed. (IOP Publishing Ltd.. Bristol, England), Vol. 97, pp. 67-78.

25. T. A. Bmme, private communication.

26. E. J. pitcher, private communication.

4 .

27. R. E. Prael and H. Iichtcnstein, “User Quide to LCS: The WIET Code System.” Los Alamos National Laboratory =port, LA-UR-89- 3014 (Septemba 1989).

28. P. Apron, s‘Cold Neutron Sources at l.4” Nucl. Ins. & Methods in Physics Research, A284 197.1978.

29. S.A. Maloy, W.F. Sommer, R.D. Brown, J.E. Roberts, J. Eddeman, E. Zimmcrman. and G. Wdcutt, “Prognxs Report on the Accelerator Production of Tritium Materials Irradiation Program”. to be published in the procbcdings of the TMS annual Meeting, Orlando, FL, 2/97. Los Alamos National Laboratory report JAUR- 97-831 (1997).

30. AR. S. Lillard, D. L Pile, and D. P. Butt, “Materials Corrosion and Mitigation Strategies for AFT, End of FY97 Report: L Inconel718 In-Buun Corrosion Rates From the 97 A6 Irradiation,,” Los Alamos National Laboratory report (submitted 1997).

M98004681 llllllllllll11111111111ll11 lllllllllllllll lllll1111 Ill1

Report Number

Publ. Date (11)

Sponsor Code (1 8)

UC Category (19)

1

DOE