Criticality evaluation considering nonuniformity effect using Monte Carlo perturbation method

The objective of this study is to evaluate nonuniformity effect relevant to criticality safety evaluation by means of the flattened principle of fuel importance distribution. We proposed a novel approach using an MVP3.0 perturbation function with JENDL-4.0 and then built a tool to calculate the nonuniformity effect. The tool estimated an optimum fuel distribution that corresponding to the highest multiplication factor in a homogeneity model of UO2-H2O slurry. Consequently, nonuniformity effects specified by the reactivity of a multiplication factor were as much as 0.5 to 5.6%dk/k. Further, preliminary evaluations of heterogeneity effects on optimum fuel distributions were computed using statistical geometry model incorporated in MVP3.0 and then heterogeneity effects observed in optimum fuel distributions also reached 2.3%dk/k at the maximum in multiplication factor. Thus, the effects of both nonuniformity and heterogeneity should be properly taken into account in criticality evaluations.