In-Reactor Experiments to Enhance Neutron Noise Analysis Techniques for Vibration Monitoring

The diagnostic potential of neutron noise induced by mechanical vibrations in the Zero Energy Deuterium (ZED-2) research reactor at Canadian Nuclear Laboratories (CNL) was experimentally investigated. A vibrating neutron-absorber plate was used to induce neutron flux fluctuations, measured using six in-core neutron flux detectors and an ex-core radial ion chamber. The absorber plate vibration was precisely controlled with a custom-designed miniature shaker. Results showed that oscillations at discrete frequencies generated neutron flux perturbations across the reactor core, with the strongest response observed near the vibrating plate. Flux amplitudes were frequency-dependent, with higher responses at lower frequencies. Even small plate oscillations of 0.2 mm (zero-to-peak) produced detectable flux variations up to four fuel channel sites away. The preliminary results of this study are the first to experimentally demonstrate harmonic generation—a non-linear phenomenon that occurs under conditions of significant neutron perturbation.