Developing reliable and safe reactor coolant pump seals

Reactor coolant pumps (RCP's) are the pulsing heart of a nuclear power plant - essential, but generally unobtrusive. When their seals fail, however, it becomes painfully evident how fragile is the plant's dependence on a few micrometers of fluid and a few lightbands of flatness. Recent reliability studies in the US show mean capacity factor losses due to RCP seals of around 1% for PWR plants and 1/2% for BWR's. Seals in early CANDU plants were no better. At the same time, there were good reasons (heavy water and on-power refueling) why seal unreliability could be particularly costly to CANDU. AECL therefore began a major effort to understand seal performance in the mid sixties and proceeded to develop improved designs for nuclear service. These 'CAN-seals' began being installed in Canadian plants ten years ago, and four year lifetimes are now being achieved consistently, as illustrated by data from the four unit Bruce-A plant. In the fourteen units now using CAN-seals, all with Byron Jackson (BJ) pumps, only about twelve outage days can be attributed to the seals in over sixty reactor-years of service. This represents less than 0.1% mean capacity factor loss, and is an order of magnitude better than US experience. There have also been no serious leakages or spills. In this paper, the CANDU RCP seal experience, the methodology for attaining reliable long RCP seal life and the adaptability of this technology to LWR's are described and discussed. The objective is to suggest how others may achieve savings in downtime and higher integrity of the reactor coolant system through improvements to their RCP seals