Degradation mechanism of check valves in nuclear power plants

A large amount of deposit was detected at a 6-in. check valve installed in a nuclear power plant. To identify the origin of the deposit, the chemical composition of the deposit was analyzed. In this paper, in order to find out the degradation mechanism of the 6-in. check valve, vibration and temperature monitoring of the check valve are carried out during plant heat up and standby conditions. And some degradation mechanisms of the check valve are investigated. Results show that the degradation was caused by valve chattering due to the acoustic resonance.