Validation of an MCNP4B whole-reactor model for LWR-PROTEUS using ENDF/B-V, ENDF/B-VI and JEF-2.2 cross-section libraries

A detailed three-dimensional, continuous-energy MCNP4B model of the LWR-PRO TEUS critical facility has been developed for the analysis of whole reactor characteristics using ENDF/B-V, ENDF/B-VI and JEF-2.2 cross-section sets. The model has been applied to the determination of the critical loading, as well as the evaluation of reactivity worths for safety/ shutdown rods, con trol rods, and individual driver-region fuel rods. The initially obtained r esults for the first configuration investigated (Core 1B) indicated that, f or the same geometrical and materials specifications, the ENDF/B-V data lib rary yields the closest critical prediction (discrepancy of 640+/-40 pcm), followed by ENDF/B-VI (980+/-40 pcm) and JEF-2.2 (1340+/-40 pcm). The diffe rences in results between the three data libraries were studied by consider ing the contributions of individual materials to the neutron balance. U-235 and U-238 cross-sections from JEF-2.2, for example, explain an effect of s imilar to 400 pcm. Refinement of the materials specifications in the MCNP4B whole-reactor model, in particular the impurities assumed for the graphite driver of the driver and reflector regions, has been shown to reduce the f inal discrepancy of the ENDF/B-V based k(eff) result to similar to0.2%. The MCNP4B results for relative reactivity effects, such as control rod worths , are found to agree within experimental errors with the measured values. ( C) 2001 Elsevier science Ltd. All rights reserved.