Verification of Modified SCDAP/RELAP5 Against CANDU Fuel Deformation Experimental Results

Two new models for treating the fuel channel during the early phase of a severe accident in CANDU reactors were recently created and tested in SCDAP/RELAPSIM/MOD3.4. These treat the deformations phenomena and the possible relocation of metallic melt mixture inside the fuel channel, respectively. The horizontal relocation model consists in a series of modifications in the original Relocation-Flow-Solidification (LIQSOL) model in SCDAP code. The purpose of the paper is to apply the code to an experiment dedicated to CANDU fuel bundle behavior during degraded cooling and to attempt a validation of the model. The work generates and discusses the results of the modified SCDAP/ RELAP5 on a particular experiment in which a 37-element CANDU bundle was subjected to superheated steam inside a ballooned pressure tube. The focus is on the temperature evolution, the hydrogen accumulation and the metallic melt final relocation geometry.