Vacuum Drying Strategies for CANDU Power Plants

Abstract

Nuclear power plants often require prolonged maintenance or refurbishment outages in order to replace or refurbish various critical components. In order to isolate key piping systems in a dry state, various draining and drying techniques can be applied (e.g. dry air purge, drying by heating). Vacuum drying is a technique that reduces the temperature at which evaporation can occur by lowering the air pressure within the piping. The drying of either light or heavy water results in a significant reduction of radioactive dose, emissions and associated hazards during maintenance. However, specialized equipment (vacuum pumps, heat exchangers, heaters, etc.) are required in order to successfully implement vacuum drying in the primary heat transport or moderator systems in a CANDU plant. This paper explores vacuum drying strategies and equipment considerations across previous nuclear refurbishment outages and outlines some recommendations for future outages (primarily the Ontario Power Generation’s Darlington Unit 2 Refurbishment).