Monte Carlo analysis of the propagation of fusion neutrons in a high enriched uranium system

Abstract

Monte Carlo methods were used to calculate experimental observables related to the propagation of pulses of fusion neutrons in a compact and highly enriched (90%) subcritical system. These observables are the amplitude and phase of the Fourier transform of the detection rate of a 3He moving detector, they correspond to the propagation of neutron waves excited by a sinusoidal neutron source. The MCNP code was used to model in great details all the heterogeneities of the experimental set up allowing in particular to have a good model of the neutron leakage in the direction perpendicular to the propagation.The very good results of the comparison with the experimental results contrast with previous comparisons with diffusion and transport theory models. The Monte Carlo modeling allows a full analysis of neutron wave experiment in space, time and energy allowing to define asymptotic regions where global complex wave vector exists. We propose to use the extensive literature of neutron wave experiments for further benchmark of MCNP.