Comparisons for benchmark calculations with MCNP4C libraries based on ENDF/B-VI.8, JENDL-3.3, and JEFF-3.0

The comparative study on the neutron data libraries processed for MCNP4C code has been performed with the latest evaluated nuclear data libraries ENDF/B-VI.8, JENDL-3.3, and JEFF-3.0. The benchmark calculations for the libraries have been conducted for 91 criticality benchmarks established for validating MCNP library by LANL. Out of these benchmarks, 11 assemblies have been selected to clarify the cause of large differences among three MCNP4C libraries. For the fast systems loaded with highly enriched U-233 or U-235, the effective multiplication factors resulting from the use of JENDL-3.3 or JEFF-3.0 have been increased due to the large U-235 fission reaction rates in the fast energy region. For the fast assemblies reflected with normal uranium, the keff's by JENDL-3.3 or JEFF-3.0 have a tendency to decrease from the large capture and small fission rates of U-238. Considering the use of unresolved-resonance probability tables, the benchmark results for fast assemblies including W-isotopes of ENDF/B-VI.8 or U-238 of JENDL-3.3 tend to excessively increase the keff's because of the small U-238 capture rates or the large U-235 fission rates