Investigating the propagation noise in PWRs via closed-loop neutron-kinetic/thermal-hydraulic noise calculations

Abstract

Neutron noise induced by propagating thermal-hydraulic disturbances (propagation noise for short) in pressurized water reactors is investigated in this paper. A closed-loop neutron-kinetic/thermal-hydraulic noise simulator (named NOISIM) has been developed, with the capability of modeling the propagation noise in both Western-type and VVER-type pressurized water reactors. The neutron-kinetic/thermal-hydraulic noise equations are on the basis of the first-order perturbation theory. The spatial discretization among the neutron-kinetic noise equations is based on the box-scheme finite difference method (BSFDM) for rectangular-z, triangular-z and hexagonal-z geometries. Furthermore, the finite volume method (FVM) has been used for the discretization of the thermal-hydraulic noise equations, which comprises the fluctuations of all the coolant parameters, as well as the radial distribution of the temperature fluctuations in the fuel, gap and cladding.Based on the discretized governing equations and the proposed solving procedure, the closed-loop noise calculations have been performed (using NOISIM) for the case study of a typical VVER-1000 reactor core and the numerical results are presented and analyzed for different scenarios. The noise sources include the inlet coolant temperature and velocity fluctuations, in addition to the power density noises. Moreover, the space- and frequency-dependence of the propagation noise are studied in this paper.