Edge-wise perturbations to model vibrating fuel assemblies in the frequency-domain using FEMFFUSION: development and verification

Abstract

[EN] The mechanical vibrations of fuel assemblies have shown to give high levels of neutron noise, triggering in some circumstances the necessity to operate nuclear reactors at a reduced power level. This behaviour can be modelled using the neutron noise diffusion approximation in the frequency-domain. This work presents an extension of the finite element method code FEMFFUSION, to simulate mechanical vibrations in hexagonal reactors in the frequency domain. This novel strategy in neutron noise simulation is based on introducing perturbations on the edges of the cells associated with the vibrating fuel assemblies, allowing to model the movement of these fuel assemblies accurately and efficiently, without the necessity of using locally refined meshes. Numerical results verify the edge-wise methodology in the frequency-domain against the usual cell-wise frequency-domain model and the time-domain model. The edge-wise frequency-domain methodology has also been compared to other neutronic codes, as CORESIM and PARCS.