Reactor coolant pump seal leak rate simulation

Hydrostatic seals so-called leakage controlled seals are applied as the No.1 seal to RCP (Reactor coolant pump) for PWR type plants in Japan. The No.1 seal is a shaft seal to keep stiff and small gap between rotating and stationary parts and to restrict leakage through it. The leak rate of the No.1 seal is one of the most important informations to diagnose the RCP operating. But observed operating data of the leak rate seems to be very complicated; for instance, on some occasions, leak rate is directly proportional to the seal water temperature but on anther occasion it is inversely proportional to it. In order to make clear this phenomenon and to develop a method to estimate the leak rate, principal causes of the phenomenon are discussed and evaluated sensitivities of various parameters to the leak rate analytically and experimentally. Combining these elemental data, computer simulation of leak rate variation is carried out. Applying actual inlet temperature data to this simulation program, leak rate is calculated and compared with the pump operating data. The results calculated agree well with the measured data. It is verified that the friction force between the secondary seal and the inset affects the leak rate variation, and that the simulation by the simple model in which the time constants and sensitivities are predetermined analytically and experimentally is effective to estimate the seal leak rate variation with the seal water temperature. (author)