Localization of a Noise Source in VVER-1000 Reactor Core Using Neutron Noise Analysis Methods

In this paper, localization of a noise source from limited neutron detectors sparsely distributed throughout the core of a typical VVER-1000 reactor is investigated. For this purpose, developing a 2-D neutron noise simulator for hexagonal geometries based on the 2-group diffusion approximation, the reactor dynamic transfer function is calculated. The box-scheme finite difference method is first developed for hexagonal geometries, to be used for spatial discretisation of both 2-D 2-group static and noise diffusion equations. The dynamic state is assumed in the frequency domain which leads to discarding of the time disrcetisation. The developed 2-D 2-group neutron noise simulator calculates both the discretised forward and the adjoint reactor transfer function between a point-like source and its induced neutron noise, by assuming the noise source as an absorber of variable strength type. Benchmarking of the mentioned neutron noise simulator revealed that it works satisfactorily. Finally, by using the inversion method of reconstruction, the location and values of a noise source of the type absorber of variable strength (or reactor oscillator) in VVER-1000 reactor cores are determined. Accuracy of this method is highly acceptable.