Analysis And Solution Study On Reactor Core Thermocouple Seal Failures

Thermocouples in nuclear core are used to measure refrigerant temperature of given fuel components and the real-time information is feed back to main control rooms. The seal between the reactor vessel head penetrations and guiding column is a part of the main system pressure boundary. Its reliability is of great significance for the rigor and security of the nuclear power plant main system. The combination sealing structure of dish gasket (CONOSEAL) and seal ring (GRAYLOC) was used in Qinshan Nuclear Power Plant for the reactor core thermocouple seal. This seal structure have occurred many leaks defects, although the status of these defects in a controlled range, each nuclear power plant is still attaches great importance to and do possible efforts to eliminate.This article by a comprehensive analysis of the eleventh discovered during the refueling outage of the Qinshan nuclear power plant reactor core thermocouple sealed structure leakage defects, and domestic and international experience feedback analysis to find out the defects in various possible influencing factors and the possible consequences. Structural features works by combination of CONOSEAL and GRAYLOC, sealing structure analysis, there may be parts of the combination of the sealed structure defects, the assembly process, the torque setting deviation, system operating parameters change possible impact factor analysis, and develop a targeted inspection and treatment measures, including parts critical dimensions detection method to prevent the sealing structure assembled people due to the mistakes of the precautions and procedures, sealing structure the tightening torque assessment and pulling force test method.These improvements and control measures, the Qinshan nuclear power plant in running practice over the next three years, the core thermocouple sealed structure does not happen again any leakage problems taken these measures to be effective, ensure the primary circuit pressure boundary integrity and reliability of the nuclear power plant, has played an important role in control of the main system leak rate. The same time, the proposed parts critical dimensions detection, sealing structure assembled people because of the mistakes precautions and procedures, methods of the seal structure tightening torque assessment and pulling force test can prevent other using CONOSEAL and GRAYLOC combined thermocouple sealing structure of nuclear power plants have a certain reference.