An assessment of RELAP/SCDAPSIM/MOD3.2 using bundle heating and melting experiments with irradiated fuel

The RELAP/SCDAPSIM code, designed to predict the behavior of reactor systems during normal and accident conditions, is being developed at Innovative Systems Software as part of the international SCDAP Development and Training Program (SDTP). Although the SCDAP models have been widely validated against a variety of bundle heating and melting experiments over the past 20 years, the results of a recent International Standard Problem Exercise (ISP-46), based on the Phebus FPT-1 experiment have indicated that the currently available models may significantly underpredict the slumping of the irradiated fuel rods under certain conditions. To determine the cause for this discrepancy, the SFD 1-4 experiment, which used a bundle design similar to the FPT-1 experiment was reviewed and the results were compared. This paper briefly reviews the results of the ISP and SFD 1-4 RELAP/SCDAP calculations, compares the FPT-1 and SFD 1-4 experiments, and discusses the implications of the results for the analysis of LWRs under severe accident conditions. (author)