Critical Heat Flux Variations on Surface of a CANDU Calandria Tube

Abstract

In a CANDU reactor in a critical break LOCA scenario, the possible contact of the hot pressure tube (PT) with the calandria tube (CT) could cause rapid redistribution of stored heat from the PT to CT and a large heat flux spike from the CT to the moderator fluid. For conditions where subcooling of the moderator fluid is low, this heat flux spike can cause dryout of the CT and detrimentally affect channel integrity if the CT post-dryout temperature becomes sufficiently high to result in continued thermal creep strain deformation. A mechanistic CHF model has been applied to predict local critical heat flux on the CT surface for such conditions. The model shows good agreement with empirical correlations.