Research on the Propagation Characteristics of Neutron Noise Under Different Core Design

Neutron noise in pressurized water reactors (PWRs) is mainly induced by fluctuations in macroscopic neutron cross-sections, which can be triggered by various factors such as vibrations of reactor internals. Existing studies mostly focus on calculation methods and software development of neutron noise, as well as in-core inversion diagnosis of noise source. Given the considerable differences in core design between Chinese PWRs CPR1000 and HPR1000, analyzing their propagation characteristics of neutron noise is significant for in-core anomaly detection and diagnosis of specific reactor types. This paper establishes a high-precision calculation method of neutron noise based on the transient neutron diffusion equation and Fourier transform technique. By simulating noise sources from macroscopic cross-section fluctuations, time-dependent relative power of each fuel assembly is obtained, and the amplitude and phase distribution of power fluctuations is derived via Fourier transform for propagation characteristic analysis. Simulations are conducted with assembly vibration noise sources for first-cycle and equilibrium-cycle cores of the HPR1000 and CPR1000. Numerical results indicate that propagation characteristics of core neutron noise are mainly dominated by noise source location and core configuration, with minor influence from burnup.