Refilling and rewetting of horizontal fuel channels

The core of CANDU-PHW reactors consists in part of an array of horizontal fuel channels that are individually connected by feeder pipes to headers located above the core. In a loss-of-coolant (LOCA) accident, various flow and heat-removal conditions are possible. To investigate the processes associated with the refilling phase of a LOCA, experiments have been done on full-size channels containing electrically heated rod bundles. The physical phenomena observed in the experiments are described, with emphasis on the modelling requirements. At high refilling rates, homogeneous equilibrium models are shown to be in good agreement wiht the experiments. At low refilling rates, the flow in the channel is initially stratified, consisting of steam and water streams with different velocities and temperatures. An unequal velocity, unequal temperature (UVUT) model of separated steamwater flow is described, that incorporates the essential physical phenomena. Comparisons between prediction and experiment are presented