Potential jamming of recirculation system valves in the safety injection system (SI) and containment spray (CS) systems for 1300 MWE/P'4 PWRs
By the end of the year 2000, an anomaly has been found in the recirculation system valves of the Safety Injection (SI) and Containment Spray (CS) systems on twelve French 1300 MWe/P'4 pressurized water reactors. This anomaly might block the valve and prevent its opening, especially in case of loss of coolant primary accident (LOCA), due to an operating stress exceeding the value considered for motorization sizing. The reason is a high overpressure in the valve body caused by a temperature rise of the water contained in the body ("thermal binding"). This fault constitutes a potential common-mode failure risk, which could cause the inoperability of the recirculation flow both redundant tracks of the SI and CS systems. The Institute for Protection and Nuclear Safety estimated the core damage risk in this situation at 3x10-4 per unit per year. The emergency of processing the generic anomaly led the utility Electricité de France (EdF) to develop a modification in two steps (temporary solution and final solution).