Study on early core anomaly detection system using nuclear instrumentation; Study on core anomaly detection system based on fluctuation characteristics of neutron flux monitors in JOYO

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A neutron flux monitor can be effective for early detection of reactivity anomalies in a FBR core. For instance, when a local blockage causes a bubble, there is a slight reactivity change in the high frequency band. It is important to understand the fluctuation characteristics of neutron flux monitors. Analysis of the JOYO reactor showed that flux-monitoring fluctuations are pink noise. These noise characteristics drive the requirements for the JOYO reactor anomaly detection system. The system requires fast time resolution and analog to digital resolution with sufficient dynamic range. A real time arithmetic unit is needed to compare the flux monitor signal with signals from normal conditions. This report describes the characteristics of neutron flux monitor signals and the anomaly detection system designed to analyze them.