Experimental Analysis of Coherent Neutron Flux Fluctuations Observed in a Pressurized Water Reactor

Plant signals from the Borssele nuclear power plant in the Netherlands were analyzed to investigate the characteristics of neutron flux fluctuation in the low-frequency range 0 to 0.5 Hz, focusing on its spatially coherent motion. The second azimuthal oscillation mode was observed at the frequency of ∼0.03 Hz while the corewide oscillation mode was at ∼0.1 Hz, and the fluctuation at the corewide mode was much stronger.