ENDF/B-V and ENDF/B-VI Calculations for theLWBR SB Core Benchmarks with MCNP5?

摘要

The Light Water Breeder Water Seed and Blanket critical experiments are ofrnparticular interest because they include lattices of 233U and highly enrichedrnuranium fuel pins completely immersed in water. All eight experiments havernthermal spectra.rnMCNP5 calculations have been performed for these benchmarks, usingrnENDF/B-V and ENDF/B-VI nuclear data libraries. ENDF/B-V produces goodrnagreement with the benchmark values for keff. ENDF/B-VI produces reasonablernagreement with the benchmark values but not as good as ENDF/B-V. However,rnthe ENDF/B-VI results are less sensitive to the H/U ratio.rnBoth ENDF/B-V and ENDF/B-VI substantially underpredict keff for the threerncases that have 233UO2-ThO2 blankets. The thorium contains a small amount ofrngadolinium, and the calculated reactivity worth of that gadolinium ranges fromrnapproximately -0.002 △k to approximately -0.004 △k for the three cases. Givenrnthe ambiguity in the gadolinium content and its reactivity impact, it isrnrecommended that the uncertainty in the benchmark value of keff be increased forrnthese three cases.