Implementation of a frequency-domain neutron noise analysis method in a production-level continuous energy Monte Carlo code: Verification and application in a BWR

A Monte Carlo algorithm for solving the transport equation of the neutron noise in the frequency domain has been newly implemented into a production-level continuous energy Monte Carlo code, MCNP. Using the continuous energy Monte Carlo code, accurate neutron noise calculations can be performed with fewer approximations. The implemented algorithm is based on a method that was previously developed by the author of this paper. The modified code is currently applicable to neutron noise calculations only within the plateau frequency range. The modified code is applied to the neutron noise calculations in a one-dimensional homogeneous multiplying system to verify its effectiveness through comparison with a two-energy group in-house research-purpose code. The neutron noise calculations for a benchmark model of a BWR core are performed using the modified MCNP code. The spatial and frequency characteristics of the neutron noise propagation in the BWR core are investigated through the calculations. The neutron noise near the noise source differs largely from the point kinetics because of the higher order mode effect.