Predictions of Fuel Channel Behaviour for Large LOCA in CANDU Reactors

Abstract

This paper describes a model used for fuel channel simulation during large break loss of coolant accidents in CANDU reactors. The model will be used to assess the fuel channel response under conditions in which the pressure tube is heating up and straining. The model is a detailed idealization of a fuel channel using the CATHENA two fluid code (Reference 1). The model can account for pressure tube temperature non-uniformities due to fuel bearing padpressure tube (BPIPT) contact, and for the resulting strain localization. Simulations of a 20 percent reactor inlet header break in the CANDU 6 design illustrate the capability of the model. Arbitrarily large power pulse was used to check the BP/PT model. Simulations with and without modelling of the heat transfer through a bearing pad to the pressure tube show the effect of bearing padpressure tube contact in developing a hot zone on the pressure tube. Finally, a comparison between CATHENA and HOTSPOT (Reference 2) predictions shows good agreement.