Monitoring the Technical Condition of the Self-Powered Neutron Detector of a Water-Cooled Nuclear Reactor in Static and Dynamic Modes

Abstract

Reliable operation of self-powered neutron detectors (SPND) included in the in-reactor monitoring system of nuclear reactors, in particular, VVER-1200 water-cooled reactors, allows obtaining an accurate picture of the energy release distribution in the core. In this regard, when monitoring the state of the core, the technical condition assessment of these sensors is important. However, existing monitoring methods do not allow the assessment with sufficient accuracy. The paper considers a method for optimizing the monitoring of the SPND technical condition in static and dynamic modes of the measuring circuit operation, based on determining its capacitance, the emitter generating capacity and the insulation resistance of the sensors measuring cable at several reactor power levels. Based on the sensor readings, a method for assessing the multiplying properties of the core (local reactivity) is proposed. A mathematical model of electrical processes in SPNDs is proposed, based on the equations of their electric circuit elements in static and dynamic operation modes. Based on the proposed model, calculations were performed that showed the possibility of expanding the sensors operability range. An algorithm for increasing the accuracy of determining the sensors diagnostic features is described, based on calculating the sensors electrical circuit at different reactor power levels. The possibility of estimating the local reactivity value at the installation site of SPNDs during transient modes accompanied by the movement of control rods is presented using the method of inverted solution of the reactor kinetics equation. The proposed technique will improve the accuracy of the sensors technical condition diagnosis and expand the range operability by 3-4 orders of magnitude in insulation resistance. Determining the sensors diagnostic features at different reactor power levels will allow refining the emitter generating capacity, which is important for the subsequent use of sensor readings to estimate the reactivity value.