Frequency-domain models in the SPN approximation for neutron noise calculations

Abstract

[EN] Simulations of the neutron flux fluctuations, known as neutron noise, can be performed by means of the spherical harmonics equations (SPN) approximation with higher accuracy than with the diffusion equation. In this sense, one can solve these equations in the time-domain or in the frequency-domain. This last approach permits solving the neutron noise without performing complete time-dependent simulations for monochromatic perturbations. This work presents two formulations of the SPN equations in the frequency domain, that are obtained by using different treatments of the time derivatives of the field moments. The methodology is verified with several neutron noise problems where the numerical results are compared with the time-domain computations of FEMFFUSION code. The C5G7 noise benchmark compares both SPN formulations, showing the applicability of the diffusive SPN approximation.