FULL SCALE EXPERIMENT TO DETERMINE THE THERMAL RESPONSE FOLLOWING LOSS OF COOLANT WATER FROM A FLASK CONTAINING IRRADIATED LWR FUEL

Water filled flasks, with a steel body, lead liner and internal fuel containment bottle, are used extensively to transport irradiated light water reactor fuel. If all the water was lost from the flask, then there would be a considerable increase in the thermal resistance between the fuel and the flask body, with a consequent rise in fuel temperatures. Full scale experiments have been conducted on an Excellox flask to determine thermal performance in the dry state. The experimental rig consisted of the flask fitted with electrical heaters to simulate fuel elements and instrumented to investigate temperature changes. Because of temperature limi· tations on the rig, a computer model has been developed to extend the temperature transients to equilibrium. Temperatures have proven to be appreciably lower than previously predicted and can be significantly reduced by partial replacement of water to fill the flask-bottle interspace or by increasing the air pressure surrounding the fuel. The model is being further developed to investigate the performance of flasks of similar design for different fuel arrays and loading