Haight, R.C.

Lee, J.D.

Haight, R. C.

Lee, J. D.

UNT Digital Library

. £^-}<r. rhisTtTB'p.regrint of a paper intended for publication In a journal or prb'ceodinjjjs. Since changes mayjMMrtade before publication, this pf^^^i^ntd^k^inSble with the understandingthatlt will not bei!Ift8W^ 11 produced without the permission of the author. UCRL - 75627 PREPRINT AIAJ/. 7V**/Si--( LAWRENCE UVERMORE LABORATORY University of CaKtomia/Livermore, CalHv-va Calculations of a Fast Fission Blanket for DT Fusion Reactors with Two Evaluated Data Libraries R. C. Haight J . D, Lee April 11 , 1974 -NOTICE-This report was prepared as an account of work sponsored by the United states Government, Neither the United Stales nor the United States Atomic Energy Commission, nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes a;iy warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, com­pleteness or usefulness of any information, apparatus, product or process disclosed, or represents that its use woutd not infringe privately owned rights. This paper was prepared for presentat ion a t the American Nuclear Society Meeting, April 16-19, 1974 .aSTRIBUTION Of THIS DOCUMENT IS UNLIMITED —— ——.*• , y-rrr. 'f / ••-; — QJ Calculations of a Fast Fisuion Hlc-inkct for bT 1'nuion i-ieactoj:-:; with Two Evaluated Data Libraries 1 ' 1 J.i. C. Haight and J . D. Lee Iawrence Livermore Laboratory Abstracr A conceptual fusion-fission hybrid reactor blanket of Werner and Loe haL; h?<?n investigated with two evaluated data libraries, Ine ENDF/ii-III and the: Lawrence Livermore Laboratory Evaluated Nuclear Data Library (;.;iDL). ~Jjjni-ficant differences are found for tritium breeding, z 5 9Pu breech.;., and i.-ntrgy production through fission of uranium in the blanket. These diiier-er.eec are due primarily to differences in the 14-MeV neutron-induced emission opectra as evaluated in the two libraries. Introduction In a preceeding paper,1 one of us examined various neutronic aspects of one type cf conceptual fusion-fission hybrid reactor blanket. The results in­dicated that a fast spectrum blanket has a number of attractive features, the rajor ones being that unenriched uranium could be efficiently used as a fuel ani that tritium breeding from lithium would be sufficient to replace the tri­tium burned in the D-T fusion reaction. These results were all derived from a detailed neutronics analysis which was based on an evaluated neutron data set.2 Because of the favorable potential for this concept as a power ̂ reducer., it was decided to verify the neutronics analysis using a different evaluated r.eurron data set.3 If the results had turned out the same, this paper could have been a footnote in the preceeding work. But the results were quite different. Tritium breeding according to calculations with this second li­brary would be practically inadequate to make up for that burned in fusion. Tne energy multiplication by fission in the blanket would be 26% lower, and there would be a decrease in the 2 3 9 P u breeding. These surprising differences required further investigations and comparisons of the contents of the two evaluated data sets. Evaluated nuclear data are based, for the most part, on experimental nu­clear data when they exist and upon systematics or nuclear model codes when experimental data are inadequate or entirely absent. The two data sets used in these calculations were evaluated to a large extent from the same experi­mental data and as a result the evaluations are quite similar in many respects. For example, the often measured 2 3 6U(n,f) cross section is evaluated almost identically in the two sets. Only rather small differences can be found in most of the evaluated total, fission, and capture cross sections for the ma­terials in the present problem. Similarly, only small differences exist in 'v (the average number of neutrons emitted in fission) for 2 3 5 U and 2 3 e U . The differences which do exist appear' in quantities which have not had many experimental investigations. An example is the neutron emission u^jctrum "Work performed under the auspices of the U. S. Atomic Energy Commission. following intoractic.. of 14-MeV ..eutrons with a nuclou:;. Lxcei.c '.or- „:,•. •».-cent stuJies of Koninoivlicner,'' few measurenentc had LC<TI made oi i:.i:. ';'J....ity and evaluation:; of it relied on neutron evaporation model:; or •syjii.:^: '.'.-... Yet, these emission spectra appear to be especially relevant for tho ii:.:.or.-fissior. hybrid and in fact account for most of the differences in the calcu­lated parameters. Calculation A conceptual hybrid reactor model of Werner5 and Lee1 was ir.vestig--\ec by means of Monte Carlo calculations. To illuminate various asr^cts, the spherical system was divided into IS zones as indicated in Fig. -• ZCTA: 2, 4, 6, 8, 10, 12, 14, and 18 are only 0.001 cm thick each and were included to investigate the neutron spectra. The materials and densities arc lifted in Table I. Where more than one element is present in a zone, ar. haT.oge.-iized mixture is assumed. Two data libraries were used. The DIDF/3-III j.i:,rnry: <ITJ± ti.<-- Laveur.ee Livermore Laboratory (LLL) Evaluated Nuclear Data Library (i-.'.'.iL)5 wore pro­cessed into 176 group-averaged data by the LLL jjiocessiiig co<.e CLY./..' A î -ii flux weighting spectrum was used for each group. Calculations- of the hybrid systems were perforated W-'L.I „:.I.- ..•<>..• TAJ-'."' which Joes an analogue Monte Carlo calculation. The soiarce u: i'.-;•:. .' .•».-.- ,:̂ ;.u was assumed to be uniformly distributed within the 320 on radiu;.. LuK.plc:. of 10,030 fusion neutrons were studied for each calculation. The cod'.- com­puted the numbor and spectrum of neutrons entering designated zones, the num­ber of each type of reaction within a zone, and the probability that the reaction was initiated by a neutron of a particular energy. Results The calculated results are given in Table II. For tritium breeding, calculation with the ENDF/B-III yields tritium breeding which is tx\ t;:e or-er of 20% less tlian given by the calculation which used the CNDL. The ior?..er-result would imply, assuming 100% recovery, a bare equality between •critiuv. burned and that prcduced. On the other hand, the latter result is c comfort -ably adequate breeding factor. (It should be noted that in this .-need, unlike the so-called "standard CTR blanket" design,6 the 7Li(n,n't) reaction contri­butes little to tritium breeding.) A greater disparity occurs in the number of fissions where t'r.̂  -IXcVi-lll result is 26% lower than the calculation with Er.DL. This result varies only slightly for the different zones which contain uranium. Most of the fissions in this design occur in the abundant 2 3 < U isotope which has a threshcl"' for fission of about 1.5 MeV. It is in this isotope where the largest difference occurs in the two calculations. 2 3 9 P u is bred by the usual sequence of reactions 2 3 3L'(;-.,Y) : J JL' -» *J-:;p -* 2 3 9i'u. THUS, the number of neutron captures on * 3 0U give:-; the ;,ju'-.\,niur.-breeding factor. For this quantity, the two calculati&nc. give ^ ^ . u diifer-ing only by 7% with the ENDL result again being the larger. Figures 2-6 give comparisons of the calculation for the quantities of interest as a function of the neutron energy which initiates the various reactions. Representative zones have been chosen for iiiustraticr.. These plotted results are proportional to the particular reaction crcsi secticr. weighted by the neutron flux spectrum in the zone. Figures 7 and 2 ̂ ive tra spectra of neutrons entering zones 6 and 10. Except for a factor c: iA.-.'v2, these litter two spectra are equal to the flux spectrum at t..-jce two narrow zones, or.e being midway through the fissile material and the otr.er i'-eing 13 err. into the predominantly lithium-filled zone. In all those fibres, J.:<? E>CF/bdII results and the ENDL r\ ults differ in magnitude and, -or the lew nurrjerers zones, in shape. :'i.VU:.!: ion The rather large differences in the results calculated with t.iu :-.L:V;',-'.III iinJ the L\nJL appear to be due to differences in the neutron ttrdsoion r^vcra Induced by 14-.MeV neutrons. After the first interaction ol 14-tfeV -.eut."onu ::.-. •.;;.>:.".::v.:.i.-;: uranium, the cidssion spectrum if- tint of Fi;j. 'J- ''•<•'- :.ol'.r; til." :v..L:\3:v: .:l:ov«j 2 MeV are more pix>bablc according to th<j i-.'Li. t:. ..-i .ir.-oorvj-.!:•<•. ii- ii»' liXW/i'-i ri. A very similar result holds for- the i4-KO/ i.vJ>io«/i c:d:;i;.Lor. ..pectrum I iinn the SUIT, of the structural iiuterdijl:;, nioi.''«•;. -jr.''. stain­less steel. (The «iij;;i;ion spectrum o! iron has Iveon dr.'.u:;.-....; .jt i'--n;'.l:i by L. ". ;«'Ui-jcu et a_l. s). The differences in the evaluation:; for lithium at lu MeV are in the iiLiw direction but much smaller. These spectral differences work on the S J 0 U fission probability, .''ecoll that the : 3 6 U fission cross section has a threshold at 1.5 KeV above- which it risej to about 0.S5 barns, Near 6.3 KeV, the threshold for (r.,n'!) it iV-Luv-eJ arJ the total fission cross section rises to about 1 barn. Lear li.B XeY, the cross section rises again to about 1.4 b a m s . Tnus, the raze ener­getic the neutron emission spectrum (i.e. that in 2 © L ) the snore likely the secondary neutrons will induce fission. The total number of 2 " U fissions is th.u. greater in the calculation with the ENDL data. Similar considerations hole for the fission of : l 5 U . Fcr the reacfions 6Li(r.,t) and 2 I*U(n,Y). the cross sections ir. -.he XeV rai^e decrease with increasing neutron energy. Tnus., the nuT-ber o: these reactions is determined by the numiwr of neutrons below the fusion source peak, iiecause there are .Tore fissions per fusion neutron in the calculation with ;X.'L, there are more neutrons in the system per fusion. The calculation vita LXLL therefore give-., rrnre trititaa and 2 , * P u breeding. We note that reac­tions below 1 MeV are not very important because the absorption by lithitar. depletes the flux at these low energies. In conclusion we have found that the l4-?<e7 neutron-induced emission spectra data are crucial to the calculation of a fusion-fission 5-.yb.--id reactor. Relevant data1* for many materials have recently beoonve available and could, be included ir. evaluations. Finally, we note that the amission spectra find es­pecially good tests in pulsed sphere experiments v;here the sphere:; are r.o larger then a few mean oaths in radii. Cf the r.-iaterials under consideration here, spheres of iror.9>'"> and isotopes of uranium and lithiur.-.'c have beer. investigated at 14 KeV. The emission spectra above 2 MeV, for thu lithiur. spheres are calculated 1' quite well with either the E-3F/3-III or- t.-.e Il'LM. The spheres or' iron 9 or of the uranium isotopes' 2 en the other hand are calculated ~:ech better with ENDL than with EffiF/B-III for emission energies above 2 XeV. References J.L. Lee, "Xeutronics Analysis of a 2500 XVM Fast Fission Natural I'rania.-Blanket for a DT Fusion Reactor." Proc. this conference, to be published. M.K. Drake, "Data Formats and Procedures for the ENDF Neutron Cross Section Library," 5KL S0274 (T-501), vol. 1 (1970); D.E. Cullen and P.J. iaavac, "EL'OF/3 Cross Sections," BNL 17100 (1972); 0. Ozer and D. Garber, "ENDF/5 Su.™ary Documentation," BNL 17541 (1973). 3J\.J. Howerton, R.J. Doyas, T.C. Michels, and S.T. Perkins, "An Integrated Sy^ter. for Production of Neutronics and Photonics Calculational Constants," I'C.-.L 50400, vol. 4 (1971), "Evaluated Nuclear Cross Section Library." \J.L. .<.::;..e:v;ii;n<.:.-, ".\eutron Spectra Dratted by 2 3 0 ! \ i , 21i\J, : 3 5'J, ;':;, N"̂ , Fe, .•'-.::, .*:•... C Iivadiateo by 14-KeV N'euU-ons," UCRL 51232 Lawrence Liverwort Li. -'-:..teny, Ji\.'i!. '.vi-:»-r fiiiJ L.D. i in iLjboroujih, "A MuJuiai' Fi^c i.oii-l"ii:.lori Wy.Ji-J'. :;..«-.y..-i," to Lu published. ".;..-. iViy.i:;, T.C. Nii'lu.-.!::, S.T. I'urkin:;, .uid K.J. IkM-.rUM, "f\t: Jt.i'r.'-'i<:'J ::*.-:tcin U'i- !'iwhicti.on of Ncutroiuci; olid Photonic;: CtaJtjiiJ.rr.I.'JU.• 1 <>.iii-.L.ini-.," w.. 5 (1971) CLYDE, a Code for the Production of Calculai Lcnal Coir-unii-1TC;II Nuclear Data." We are grateful to R.J. Doyac for assistance with t;,c w-odi2 CLYDE. 'E.F. iMechaty and J.R. Kimlinger, private coircnunieation. Wo art: ;jrmtefu_ to Messrs. Plechaty and Kimlinger for assistance with the code T/J:';'. BD. Steir.er, "Analysis of a Benchmark Calculation of Tritium Breedin;; in a Fusion Reactor Blanket: The United States Contribution," OKJL-TX—.^77 (1973). *L.F. Hansen, J.D. Anderson, P.S. Brown, R.J. Kowerton, J.L. iCarrmei'cier.er, C.H. Logan, E.F. Plechaty, and C. Vtong, Nucl. Sci. Eng. Sl_, 278 (1S71). , 0C. Wong, J.D. Anderson, P.S. 3rcwn, L.F. Hansen, J.L. Kanmerdiener, C.X. Logar., and 3. ?ohl, "Livermore Pulsed Spher* Program: Progm.-. £>u;...ary through July 1S71," UCRL-511H4 (1971). 1!.:\.J. iicwerton, private conmunication. !2.\.J. Howarton and M.H. MacGregor, "Evaluated Neutron Reaction Data for Urari.wr.-23S," UCRL-S1427 (1973). Table I - Material Composition Zones Density (gm/cm3) 1 1 0 - 7 2-7 13.3 -15, 17, 18 1.07 16 2.0 C 1.0 19 S.82 Material Atom Fractio: D + 1 (a) 2 3 e u C.710 »*u 0.005 'Li 0.127 6Li 0.01C Fe 0.073 >Ji 0.017 Nb 0.060 'Li 0.730 sLi 0.062 Fe 0.083 Ni 0.020 Nb 0.055 H 0.475 B 0.003 C 0.21.3 Fe 0.260 (a) Since the ENDF/B-III library does not contain tritium as a material, pure deuterium was assumed in Zone 1. il>li' II - Ko.irl. inn:: l<y Zuru; [ X T I'M:; ion K.-.i.-l ion Zone UNDP Tritium lirtjf VIW10 (jjii,r/i:iii>i.) cL:'.(n,t) 3 0.044 0.053 (j.b'i 5 0.039 0.047 b.b'i 7 0.051 0.064 0.80 9 0.159 0.205 0.78 XI 0.13? 0.172 Q.77 13 0.219 0.273 0.80 15 0.216 0.254 0.6S 17 0.079 0.093 0.80 Total 0.94 1.16 0.81 7Li(n,n't) Total 0.06 0.07 0.8 Total Tritium Breeding 1.00 1.23 0.81 2 3 9 P u breeding 2 3 a U ( n > Y ) 3 0.675 0.705 0.96 5 0.603 0.628 0.96 7 0.847 0.944 0.90 Total 2.13 2.28 0.S3 Fission 2 3 8 U fission 3 0.278 0.372 0.75 5 0.171 0.239 0.72 7 0.153 0.228 0.67 Total 0.60 0.84 0.72 U fission 3 0.039 0.044 0.88 5 0.C34 0.038 0.89 7 0,044 0.052 0.85 Total 0.12 0.13 0.87 al fission 0.72 0.97 0.74 Figure Options 1. Zoning of the fast fission blanket. 2. Li(n,t) reactions versus neutron energy - zone 5. 3. Li(n,t) reactions versus neutron energy - zone 11. 238 4. U fissions versus neutron energy - zone S. 235. 5. u fissions versus neutron energy - zone 5. 238 6. U captures versus neutron energy - zone 5. 7. Spectrum of neutrons entering zone 6. 8. Spectrum of neutrons entering zone 10. 9. Spectruri of neutrons after one interaction of a 14-MeV neutron with natural uranium. Neutron source o 2 3 4 5 6 o in oo co 1 -o o Zone 9 10 D.T [ U.Li.Nb.SS — - J - a - — -Material Fig. 1 11 12 13 14 15 16 17 1& 19 o o o co § cm •Li.Nb.SS Nb SS -Fe.C.H.B A 4 6 8 NEUTRON ENERGY-MEV 10 12 14 F i g . 2 L I - - 6 ( N , T ) REACTIONS PER MEV / 14 MEV SOURCE NEUTRON 4 6 8 NEUTRON ENERGY-MEV 10 12 Fig . 4 .JZ: - ENDF - ENDL J — L _ L J I I I J L_l_ 10' ,-3 10-2 10" 1 0 u 10 A NEUTRON ENERGY-MEV Fig. 5 4 6 8 NEUTRON ENERGY-MEV 10 12 14 Fig . 6 4 6 8 NEUTRON ENERGY-MEV 10 Fig . 7 4 6 8 NEUTRON ENERGY-MEV F i g . B 4 6 3 NEUTRON ENERGY-MEV 10 12 14 F i g . 9 

Calculations of a fast fission blanket for DT fusion reactors with two evaluated data libraries

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