Sealing Solutions for an Aging Reactor

There are an increasing number of nuclear reactors around the world operating well beyond their original design lives. Some pump seals supplied by original equipment manufacturers are either no longer available or their performance does not meet current requirements. This paper describes both the testing and operational experience of two nuclear pump seals that have been developed by AECL to replace the original equipment manufacturer’s seals in AECL’s National Research Universal reactor, which has been operating since 1957. The two seals described are the main heavy water pump seal and the heavy water degassing pump seal. The main heavy water pump seal is a tandem seal containing two identical, but 180° offset, eccentric seals of 95 mm balance diameter. The requirements were low pressure (0.3 MPa), low leakage (< 0.2 mL/min) and long, reliable lifetime (seven years). The seals were arranged to put full pressure across the outboard seal initially, with the inboard seal providing complete back up in the event of an outboard seal failure. Laboratory testing and operational performance, since initial installation in 1993, is described. The heavy water de-gassing pump seal design is based upon the main heavy water pump seal (a tandem seal containing two identical, but 180° offset, eccentric seals) but its balance diameter of 65 mm is much smaller than that of the main heavy water pump seal. Laboratory testing and operational performance, since initial installation in 2001, is also described.