Consistent evaluation of modern nuclear data libraries for criticality safety analyses of thermal compound low-enriched-uranium systems

This paper addresses the assessment of MCNPX-2.5.0 criticality calculations using continuous-energy neutron cross-section libraries based on ENDF/B-VI.8, JEF-2.2, JENDL-3.3, and the recently released ENDF/B-VII.0 and JEFF-3.1 data files. For this purpose, validation calculations were performed for a suite of benchmarks from the International Handbook of Evaluated Criticality Safety Benchmark Experiments. The benchmarks were selected on the basis of their similarity to designs found in today’s Light Water Reactor (LWR) compact storage pools and transport casks and in total comprised as much as 122 cases belonging to the category of thermal compound systems with low-enriched uranium. In order to define the ranges of applicability of the used calculational methods and to detect possible trends, the spectrum-related characteristics of the modeled critical experimental configurations were analysed. It is found that the latest ENDF/B-VII.0 and JEFF-3.1 libraries improve the older ENDF/B-VI.8 and JEF-2.2 compilations significantly and both lead to values for the weighted average of the normalized eigenvalues very close to unity. All libraries have in common that any evidence of a statistically significant trend in the normalized eigenvalues versus both spectrum-related characteristics and experimental design parameters could not be found.