Failure Analysis for Wires of Coordinate Location Sensor for Control Rod in Reactors

The coordinate location sensor of control rod of XX Nuclear Power Plant failed during operation.In order to analyze the reason,it is necessary to take apart of the coordinate location sensor.Each coordinate sensor has 12 wires and each wire has a V flexure at the same position.And one wire is fractured at the top of the V flexure.In order to study the fracture reason of the wire,the microstructures of fractured,flexural and normal wires were investigated by using scanning electron microscope（SEM）,energy dispersive X ray spectrometer（EDS）,and optical microscopy（OM）.The results indicate that the wires are stress corroded,and the grain boundary became rather weak in the high temperature and high pressure environment in the reactor.Finally the wire is broken at the top of the V flexure due to tensile stress which caused by the differential heat expansion coefficient of the material.