Heat Removal Capacity for a Local Air Cooler Without an Active Fan (Semi-Passive Local Air Cooler)

Abstract

Local air coolers (LACs) in CANDU nuclear power plants (NPP) contain an electric fan that forces containment vapours/gases across a set of water cooled finned tubes. LACs are one of the ultimate heat sinks for a NPP containment, but a loss of electrical power or elevated containment temperatures would render the electric fans inoperable. A set of experiments were performed at Canadian Nuclear Laboratories that demonstrate with available cooling water flow, the LACs can operate in a semi-passive mode to provide 26% to 60% of the cooling capacity of a fully functioning LAC at a bulk vapour temperature of 90°C, 100% relative humidity and atmospheric pressure. This has the potential to condense steam and maintain containment integrity during a prolonged accident at a CANDU NPP. Any safety analysis that neglects semi-passive LAC operation would underestimate condensation, underestimate hydrogen concentration and overestimate steam inerting of hydrogen combustion.