Convective Heat Transfer in CANDU Spent Fuel Racks After a Loss of Coolant

The event at the Fukushima Daiichi Spent Fuel Pools (SFPs) has renewed interest in quantifying the safety margins related to loss of coolant accidents in Irradiated Fuel Bays (IFBs). Thermal-hydraulic analyses of exposed spent CANDU fuel has been limited to a small number of bundles due to its complex bundle geometry and open rack design. This paper presents a process to predict the steady state temperature and velocity of air as it passes through a rack of spent fuel using analytical models and Computational Fluid Dynamics (CFDs) techniques. The scenario acts as lower bound estimate for the effectiveness of convection during a complete loss of coolant in a fuel bay by examining the heat-up of a stand-alone rack without flow resistance of the bundles. The correct incorporation of flow resistance is a necessary step before conclusions are made about the available safety margins of irradiated fuel bays.