Monte Carlo Simulation of Neutron Transport Applied to Criticality: Focus on Sources and Flux Convergence Issues

Abstract

Safety studies to determine criticality risk (uncontrolled multiplication of neutrons) in systems containing fissile material require the use of computer codes (software programs) that can simulate neutrons in complex three-dimensional configurations. This article describes the specific features of the Monte Carlo simulation method, used to simulate neutron transport for criticality studies conducted using the MORET code developed at IRSN. It highlights also the flux convergence issues in Monte Carlo depletion simulations.Neutron diffusion waves allow, in principle, the determination of sources of neutron flux variations in a nuclear reactor, so they can be used as an additional diagnostic tool. A model was developed to explore the properties of such waves.Preliminary results on neutron diffusion waves in CANDU reactors are presented. The results include information on dispersion relations for the neutron waves and interference effects involved in neutron wave propagation.