Analysis of TCA critical experiments for PWR MOX fuels with the TRIPOLI-4 Monte-Carlo code

Six TCA two-region critical experiments of MOX/UOX fuel arrays from Japan Atomic Energy Research Institute (now JAEA) have been utilized in this study to investigate the nuclear data libraries and the reactor physics parameters. The TRIPOLI-4 continuous-energy Monte Carlo transport code has been applied under the criticality mode to analyse these critical experiments. Recent developed options of TRIPOLI-4 code, the effective delayed neutron fraction estimation, the multi-mesh tally calculation, and the multi-grid meshed maps display are the three essential elements of this work. Comparing to the previous JEF-2.2 data library, the new JEFF-3.1.1 one produces higher and better K_eff results for the present benchmarks. Average difference in reactivity of 280 pcm has been obtained. With Probability Tables option in TRIPOLI-4 calculation a gain of 30 pcm has been observed for three of six MOX/UOX configurations. The calculated β_eff values are between 571 and 650 pcm for these TCA cores. TRIPOLI-4 calculated delayed neutrons distribution shows that the UOX driver zone contributes important delayed neutrons. Both the rim effect of fission events in MOX fuel pin level and the power distribution in MOX fuel lattice level for two TCA cores have been investigated using the new developed TRIPOLI-4 display tool. (authors)