UNCERTAINTIES ON FISSION PRODUCT RELEASE IN A LOSS-OF-COOLING SCENARIO IN A SPENT FUEL POOL WITH MELCOR 2.0

After the events occurred in Fukushima in 2011, the vulnerability of the Spent Nuclear Fuel (SNF) stored in Spent Fuel Pools (SFPs) was highlighted, and the reliability of the SA codes predictions in SFPs questioned. The present study synthesizes the main insights gained by quantifying the uncertainties and assessing outcomes’ sensitivities of a SFP analysis. Inspired by the Unit 4 SFP of Fukushima-Daiichi, a loss-of-cooling accident was assumed with the focus on fission products release. Calculations were performed with the MELCOR code, and the uncertainty propagation was articulated through the DAKOTA statistical tool. Fifteen input uncertain parameters related to fuel rod failures, their degradation and fission products release were selected. By using several data analysis techniques, some correlations between input parameters and figures of merit were noted. As expected, Xe and Cs uncertainties were qualitatively similar, while Ru release showed its own footprints. Two outcomes of the study worth highlighting here: the relevance of a consistent choice of the input uncertainty parameters set, both number and variables, was shown to be crucial in the analysis; a thorough characterization of the FOM sensitivity will likely require more than just an individual data analysis technique.