Defects Analysis of CRDM Weld in EPR Nuclear Power Plants

The control rod drive mechanism (CRDM) pressure housing in nuclear power plants is subjected to high temperature, high pressure and high radiation. The pressure housing welds is prone to crack defects, which is the focus of the in-service inspection during the overhaul. In view of the suspected defects found by Ultrasonic inspection in the pre-service inspection, supplement nondestructive test and destructive test were implemented. The results proved that the indications were metallurgical indications caused by the austenitic hardened grain with incomplete recrystallization, which is without effect on the quality of the welds. The methods of signal analysis for suspected defects were summarized.