Source Term Analysis in the Fuel Degradation Phase of PHEBUS FPT-1 Experiment using MELCOR 2.2

Abstract

A severe accident in a nuclear power plant is accompanied by complex phenomena within the containment building due to the release of various fission products and combustible gas. An accurate prediction of the source term is crucial for preventing the release of radioactive materials outside the containment building and for implementing appropriate mitigation measures under severe accident conditions. In this study, we analyzed the parameters related to the core degradation and the release fractions of fission products by benchmarking the PHEBUS FPT-1 experiment using the MELCOR 2.2 code. The simulation results were compared with experimental data of the temperatures of fuel and cladding, hydrogen production rate, and the release fractions of fission products to the containment vessel for source term assessment. The fission products discussed in this study include Xe, Te, Cs, and I classes. The predicted release fractions of xenon, tellurium, and cesium were similar to those measured in the experiments, while the release fraction of iodine was underestimated by about 20%. This indicates that further efforts in modeling with the MELCOR code are required to reproduce iodine behavior observed in the FPT-1 test. Uncertainty and sensitivity analyses are also deemed necessary for future work.