A Mechanisitic Model for Pressure Tube-Calandria Tube Thermal Contact Conductance for a Pressure Tube Ballooning Event

Abstract

During an event resulting in loss of cooling ability to the fuel such as a critical break large Loss of Coolant Accident (LOCA), pressure tubes in a CANDU® reactor could undergo ballooning deformation resulting in physical contact between the pressure tube (PT) and its surrounding calandria tube (CT). Thermal contact conductance between the two tubes plays a major role in whether CHF occurs on the outside of the calandria tube. A mechanistic model for contact conductance under transient contact pressure is developed. The resulting contact conductance transient is then compared to experimental data obtained in a graphite heater fuel channel deformation experiment. It is shown that a sustained high level of PT-CT contact conductance is not consistent with the results obtained through the developed mechanistic model.