Neutronics Analysis of Full MOX BWR Core Simulation Experiments FUBILA

Abstract

A part of the experimental program FUBILA was dedicated to the study of the core physics characteristics related to in-channel void fractions of BWR MOX assemblies at power operation. The present paper describes analysis results of the experimental data with deterministic analysis codes and a continuousenergy Monte Carlo code coupled with major nuclear data libraries. It also discusses the accuracy of the adopted analysis methods. The major findings are summarized. The calculated critical k eff 's with the Monte Carlo calculations range from 0.999 to 1.006. Those of the transport calculations with sixteen energy groups are close to those of the Monte Carlo calculations; those of diffusion calculations with the sixteen energy groups are systematically smaller by À0:4 to À0:5%Ák than those of the Monte Carlo calculations. The RMS's of differences between the calculated and measured core radial fission rates are from 1.1 to 2.2%, which are from about one to two times larger than the measurement errors. The axial fission rate distributions measured using integral gamma scanning and 235 U and 237 Np fission chambers are well reproduced by the diffusion calculation. The analysis results well reproduce the measured modified conversion ratios for the 40% void core; however, they overestimate those of the 70% void core. They tend to underestimate the measured spectrum indexes f (239 Pu)/ f (235 U) and f (237 Np)/ f (239 Pu).