European Clearinghouse: Report on Leaks and Cracks of the Reactor Coolant Pressure Boundary

摘要

Leaks and cracks of the Reactor Coolant Pressure Boundary are a clear indication of degraded conditions inside the nuclear power plants, challenging the barriers against radioactive releases into the environment. Thus it is important to investigate the existing operational experience in this kind of events. The objective is to determine the adequacy of protection of nuclear power plants against leaks and cracks and the effectiveness of the corrective actions implemented, as well as to provide recommendations on how to prevent or mitigate the impact of such events on NPP operation.Leaks and cracks in the Reactor Coolant Pressure Boundary cannot be avoided. Because of this, even the Technical Specifications (or the Plant Normal Operation Procedures) allow a limited leak rate, or a specific time of unavailability, for different systems needed for normal operation of the plant. However, any leak and crack of the Reactor Coolant Pressure Boundary which remains undetected long enough will raise particular challenges for the Systems, Structures and Components within the affected part of the Reactor Coolant Pressure Boundary. Even if the leak is timely detected, there is usually a significant impact on the overall radioprotection of the plant. In some cases, the total reactor coolant loss is important and prolonged outage periods are required for recovery. So, even in the case of successful detection of such events, to analyze them is necessary in order to fully understand the mechanism which provoked such events.This Summary Report presents the results of a comprehensive study performed by the European Clearinghouse on Operating Experience Feedback of NPP with the support of IRSN and GRS.