Neutron clustering in Monte Carlo iterated-source calculations

Abstract

Monte Carlo neutron transport codes generally use the method of successive generations to converge the fission source distribution to—and then maintain it at—the fundamental mode. Recently, a phenomenon called “clustering” has been noted, which produces fission distributions that are very far from the fundamental mode. In this study, a mathematical model of clustering in Monte Carlo has been developed. The model draws on previous work for continuous-time birth–death processes, as well as methods from the field of population genetics.