Heavy metal and fission product noble gas concentrations in spent fuel from two different PWR'S were calculated using HELIOS and compared to measured results from the literature. It was found that for the U-235/U-238 and Pu-240/Pu-239 isotopic ratios, the HELIOS calculation agreed to within the experimental uncertainty. For the Xe-131/Xe-134 isotopic ratios, HELIOS tended to overestimate the result by up to 4%. Conversely for the Xe-132/Xe-134 ratios, HELIOS underestimated the result by a slight amount ({approximately}1%). This suggests that either the fission product yields for Xe-131 and Xe-132 should be slightly altered or that the absorption cross-section for Xe-131 should be slightly increased. More analysis is necessary to determine which of these two alternatives is more appropriate. This work has shown that the accuracy of HELIOS (within 2% for heavy metals and within 4% for fission noble gases) is sufficient for most analyses

Charlton, W. S.

Fearey, B. L.

Parish, T. A.

Perry, R. T.

UNT Digital Library

,Title:Author(s):Submittedto:LosAlamosNATIONAL LABORATORYComparisons of HELIOS Calculated IsotopeConcentrations to Measured Values forSeveral Reactor Systems@cEltieo4@6~~ ;J$Q?@&plt ,,W. S. Charlton, R. T. Perry, B. L. Fearey,and T. A. Parish16th Fuel Management Systems User Group MeetingMadrid, SpainOctober 21-23, 1998——. __ .- — .— ——_——— —— —_— —-= —_— ._— =======——Los Alamos National Laboratory, an affirmative acfion/equal opportunity empldyer, is operated by the University of California for the U.S. Department of Energyunder contract W-7405 -ENG-3S. By acceptance of this article, the publisher recognizes that the US. Government retains a fIOtWdJSIVe, royalty-free iicense topublish or reproduce the published form of this contribution, or to allow others to do SO,for U.S. Government purpm%s. The Loa Alamoa National Laboratowrequests that the publisher identify thk article es work performed under the auspices of the U.S. Department of Energy. FormNo.836R5ST26291O)91DISCLAIMERThis report was,.prepared as an account of work sponsoredbyanagency of the United States Government. Neitherthe United States Government nor any agency thereof, norany of their employees, make any warranty, express orimplied, or assumes any legal liability or responsibility forthe accuracy, completeness, or usefulness of anyinformation, apparatus, product, or process disclosed, orrepresents that its use would not infringe privately ownedrights. Reference herein to any specific commercialproduct, process, or service by trade name, trademark,manufacturer, or otherwise does not necessarily constituteor imply its endorsement, recommendation, or favoring bythe United States Government or any agency thereof. Theviews and opinions of authors expressed herein do notnecessarily state or reflect those of the United StatesGovernment or any agency thereof.DISCLAIMERPortions of this document may be illegiblein electronic image products. Images areproduced from the best available originaldocument..Comparisons of HELIOS Calculated Isotope Concentrations to MeasuredValues for Several Reactor SystemsbyW. S. Charlton, R. T. Perry, and B. L. Fearey T. A. ParishLos Alamos National Laboratory Texas A&M UniversityLOS AhiKiOS, NM 87545 College Station, TX 77843INTRODUCTIONDue to its involvement in many diverse projects, the Los Alamos National Laboratory(LANL) performs analyses of many different types of nuclear systems with various fhel typesand geometries. The HELIOS1 lattice-physics code, a product of Studsvik ScandPower,performs collision-probability transport-theory calculations for nearly arbitrary geometries. Forthis reason, LANL has been investigating the abilities of HELIOS to model various reactorsystems. Previous LANL investigations2’3 have focused on comparisons between HELIOS- andMCNP-calculated multiplication factors for the Savannah River Reactor assemblies and for U02benchmarks. The work presented here is primarily concerned with the ability of the HELIOScode to predict heavy metal and fission product concentrations in spent fhel.To benchmark HELIOS’ ability to accurately perform burnup”calculations, a series ofexperimental measurements of irradiated spent fbel have been chosen flom the literature. Theseexperiments include light and heavy water moderated reactors in both square and hexagonallattices. The experiments have been modeled with the HELIOS code for burnups from O to50,000 MWd/MTU. Since the data for pressurized water reactors (PWR) is the most extensive;the PWR cases from the series of I.xmchmark experiments were the frost to be compared to theHELIOS calculations. These PWR results are presented here.MEASURED VALUESTo facilitate benchmarking of the HELIOS code for isotopic determination in spent fuelfrom PWR’S, two different PWR’S were chosen as test cases. The first reactor to be modeled.was the Obrigheirn Reactor, which is a fairly standard PWR with Siemens 14 x 14 assemblies.The assemblies modeled contained 2.83 wt% U-235 fuel with Zircaloy-4 cladding. TheObrigheim experiments consisted of mass spectrometric determination of heavy metal and noblegas fission product concentrations in fuel samples cut from various positions of selected fuel rodsfrom one assembly (BE 210). The samples were cut from four different positions in the rods(15.0, 132.8, 220.8, and 242.6 cm from the bottom of the rod). The burnup was determinedusing the following three techniques: Nd- 148 measurement, Cs- 137 destructive examination, andCs- 137 non-destructive examination.The other PWR modeled was the Trino Vercellese reactor. This reactor had severalunique characteristics. The Iiel assemblies consisted of square sub-assemblies with 208stainless-steel clad fuel pins. The reactor had cruciform-type control rods with fiel followers.Each cruciform sub-assembly consisted of 28 stainless-steel clad fhel pins with a slightly largerdiameter than those pins contained in the square sub-assemblies. The assembly modeledcontained 3.13 wt~~ U-235 fiel. The experiments again consisted of mass spectrometric -determination of heavy metal and noble gas fission product concentrations in fuel samples cutfrom nine evenly spaced positions of selected fuel rods from the assembly (No. 509-069). Theburnup was again determined using the following three techniques: Nd-148 measurement, Cs-137 destructive examination, and CS-137 non-destructive examination.The burnup determination had been estimated for both experiments between 1.5% and5.0% depending on the technique used. Because of this significant range of values, we havechosen to use a constant value of i 25%0 for all measured burnups. The experimenters estimatedthe heavy metal and fission product measurement uncertainties to be approximately t 1%.However, the spread in the data suggests that this may be anspectrometry uncertainties. Thus, we have elected to use aspectrometry measurements of* 270.underestimation of the massconstant value for all massHELIOS MODELTo calculatemodel for a pin cellthe spent fbel isotopics for the two reactors described above, a HELIOSwas generated for each reactor. These pin cell models were adjusted suchthat the pitch used resulted in a fuel-to-moderator ratio equivalent to that for an entire assembly.Numerical experiments have shown that this calculational level yields spent fuel isotopics within.0. 1% of the assembly level result. Each pin cell was modeled with nine different fbel regions,one clad region, and one moderator region, The calculations were performed for a singleirradiation at the nominal reactor power from O to 50,000 MWd/h4TU with 1000 MWd/MTUsteps. The resultant isotopics at each burnup step was allowed to decay for 150 days to allow forcomplete decay of all shorter-lived parents. The bumup calculation was performed for allactinide isotopes (U-234, U-235, U-236, Np-237, Np-239, Pu-238, Pu-239, Pu-240, Pu-241, Pu-242, Am-241, Am-242, Am-243, Cm-242, Cm-243, Cm244, and Cm-245) and select noble gasfission products (Xe-131, Xe-132, Xe-134, and Xe-136). The angular dependence at theboundary of the pin cell was discretized using 8 angular sectors. Collision probability coupling(k=O) was used for all other interfaces.RESULTSThe U-235AJ-238, Pu-240/Pu-239, Xe- 13l/Xc- 134, and Xe-132/Xe- 134 isotopic ratioscalculated by HELIOS were compared to those from the experiments for both the Trino -Vercellese and Obrigheim reactors. The Xe- 136/Xc- 134 ratio was not compared to the measuredresults due to its large dependence on operational history (which was not modeled). The otherheavy metal isotopics were either not measured in the experiments or of less interest to thisstudy. Figures 1–8 contain plots of the measured and calculated isotopic ratios versus burnup. Itcan be seen that for the U-235/U-238 and Pu-240Ru-239 isotopic ratios, HELIOS yields results.generally within the uncertainty of the measured values. For the Xe- 13l/Xc- 134 isotopic ratios,HELIOS consistently tends to overestimate the result by approximately 3-4%. For the Xe-132/Xc- 134 ratios, HELIOS tends to underestimate the result by a slight amount (- l%). Overall,the fission product noble gas ratios compare reasonably well (within +4% for all cases).CONCLUSIONSHeavy metal and fission product noble gas concentrations in spent fuel from two differentPWR’S were calculated using HELIOS and compared to measured results from the literature. Itwas found that for the U-235AJ-238 and Pu-240/Pu-239 isotopic ratios, the HELIOS calculationagreed to within the experimerital uncertain y. For the Xe- 13l/Xe-134 isotopic ratios, HELIOStended to overestimate the result by up to 470. Conversely for the Xe- 132/Xe-134 ratios,HELIOS underestimated the result by a slight amount (-1%). This suggests that either the.fission product yields for Xe-131 and Xe-132 should be slightly altered or that the absorptioncross-section for Xe-131 should be slightly increased. More analysis is necessary to determinewhich of these two alternatives is more appropriate. This work has shown that the accuracy ofHELIOS (within 2% for heavy metals and within 4% for fission noble gases) is sufficient formost analyses.ACKNOWLEDGMENTSThe authors would like to thank the contributions made by William D. Stanbro, JanePoths, and John R. Quigliano at Los Alamos National Laboratory for their comments andsuggestions. Los Alamos National Laboratory is operated by the University of California for theU. S. Department of Energy under contract W-7405-ENG-36.REFERENCES1.2.3.4.5.E. A. Villarino, R. J. J. Stamm’ler, A. A. Ferri, and J. J. Casal, “HELIOS: Angularly-Dependent Collision Probabilities,” Nucl. Sci. and Eng, 112, 16 (1992).R. T. Perry, R. D. Mosteller, and D. C. George, “Status of the HELIOS Code and Library atthe Los Alamos National Laboratory,” The Twelfth FMS User Group Meeting, Brunnen,Switzerland, May 26-28, 1993, Los Alamos National Laboratory report LA-UR-93-1673.R. T. Perry, R. D. Mosteller, P. Chodak III, W. S. Charlton, and B. T. Adams, “HELIOS:Applications at the Los Alamos National Laboratory;’ The Fifteenth F’MS User GroupMeeting, Budapest, Hungary, October 30-31, 1997, Los Alamos National Laboratory reportLA-UR-97-4272.P. Barbero et al., “Post Irradiation Analysis of the Obrigheim PWR Spent Fuel” Eur. Appl.Res. Rept. – NUCLSci. Tech. 2(l), 129 (1980).P. Barbero et al., “Post Irradiation Analysis of the Fuel Discharged from the Trino VercelleseReactor after the 2ndIrradiation Cycle, ” Commiss. Eur. Communities - NUCLSci. Tech., EUR5605e (1977),0.030.030.02ii ‘“m0.010.01Osxl0.s00.700.600.50.!2~ 0.400.300.200.100.00Erru Bars he +/- 2%.m w .0 5c0010000150a20caI 25cn20m 3500040000 45w050ccioFig. 1. U-235AJ-238 RatioBumup (MWCUMTU)Versus Bumup for Obrigheim Reactor.Emu Bars Are +1- 2%,40 5mJ 10JOU 15000 2Uoc0250w30cm25cQo 4000045000 E4WxiBumup (MWCUMTU)Fig. 2. Pu-240/Pu-239 Ratio Versus Burnup for Obrigheim0.450.400.35#K0.300.250.20&mr Ban Are +/- 2%.I o Meawwi Io 5000 1000O 15000 2oooo 25000 30000 25000 woo m 50000Burnup (MWdM41U)Fig. 3. Xe-13 llXe-134 Ratio Versus Bumup for Obrigheirn Reaetor.0.950.900.35-0.80-0.75- :~ 0.70-.-$o.&s -0.60-0.55 ~0.50- :0.45- -ErKXBars Are +1- 2%.I — HELIOSo Measured 10 5000 10000 15003 20C4)0 25000 20000 350Ca 40000 45000 51MO0Bumup (MWCUMTU).,Fig. 4. Xe-132/Xe-134 Ratio Versus Bumup for Obrigheim Reactor,?Error Sars Are +/-2%.o 5000 1Oow 15000 20000 25000 2J3000 35000 40CI)0 45000 50000Sumlsp (Mwdmlu)Fig. 5. U-235AJ-238 Ratio Versus Burnup for Trino Vercellese Reactor.0.6-0.5 10.4i 0.30.20.10.0— HEUOSO Messured40 5mo 100001 sooo2c00025000 s00m35@30400w450@3 50000Sumup (MWSUMTU)Fig. 6. Pu-240/Pu-239 Ratio Versus Burnup for Trino Vercellese Reactor.0.450.400.35.sr%0.300.250.20.Error Bara Are +t- 2%.A— HELIOSo M%aaurado 5000 10000 15000 20000 25000 3(KYM 35000 40000 45000 500000.950.900.s50.800.75= 0.70g0.650.600.550.500.450.40Bumup (MWVMTU)Fig. 7. Xe- 13 l/Xe-132 Ratio Versus Burnup for Trino Vercelles Reactor.Error Bars Ara +/- 2%,— HELIOSo Maaeurado 5000 100oil 15000 20000 25000 30000 35000 4c000 45000 5ocooBumuP (MWdMllJ)Fig. 8. Xe- 132/Xe-134 Ratio Versus Burnup for Trino Vercellese Reactor.

Comparisons of HELIOS Calculated Isotope Concentrations to Measured Values for Several Reactor Systems

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