Operating Experience With Mechanical Seals in Reactor Shutdown Cooling Pumps

The CANDU nuclear reactor has a dedicated shutdown cooling system (SDC) to remove heat from the primary heat transport system and transfer it to the high pressure service water open system. There are four individual SDC circuits, each connected to one of the four quadrants of the reactor. The four circuits are independent and each of them consists of one SDC pump and one heat exchanger. When the reactor is within normal operation, all four SDC loops are isolated but kept pressurized to the reactor inlet header of 9.7 MPa (1410 psi) and warmed up to 93°C. During reactor shutdown condition and at reactor start-up operation, the SDC pumps are in-service. They operate in several different configurations and are exposed to a number of different pressure conditions. This paper will present typical failures of the seal components.