Neutron noise analysis of simulated mechanical and thermal-hydraulic perturbations in a PWR core

KWU-PWR plants show a high level of neutron noise that usually represents added problems in their operation. The frequency region of interest is below 1 Hz, so that thermohydraulic oscillations seem to be one of the main reasons behind. Nevertheless, recently, the neutron noise has experienced an increase in its normalized root mean square that coincide in time with the introduction of a new design of fuel assembly. This fact points out that there should be some relationship between neutron noise spectral characteristics and fuel assemblies’ performance. In order to advance in understanding this phenomenon, the transient nodal code SIMULATE-3K (S3K) has been used to simulate mechanical vibrations of fuel assemblies and thermohydraulic oscillations of the core inlet flow. The simulated results obtained are neutron detectors signals which are analysed with noise analysis techniques and compared to real data.