Uncertainty analysis related to the early containment failure phenomenon for Ulchin Units 3 and 4 nuclear power plants

Up to now, even though various researches related to severe accident phenomena have been going on in Korea, research results conducted in the U.S. in the 1980s are still applied to the probabilistic safety assessment as reference materials. To invigorate the risk informed regulation and application that use probabilistic safety assessment (PSA) results and information, the quality of PSA must be improved. To improve the quality and reduce uncertainties of PSA, phenomenological uncertainty analysis of the level 2 PSA has been done using the MELCOR code. For uncertainty analyses, the MELCOR 1.8.6 model for Ulchin Units 3 and 4 nuclear power plants were developed according to their own design data. Especially, control volumes of the reactor coolant system were divided in detail to simulate the natural circulation flow phenomenon. And then, uncertainty variables that have an effect on the early containment failure phenomenon were selected through the sensitivity analysis and the expert judgment. The MELOR uncertainty engine was used to generate samples of uncertainty variables. A number of MELCOR calculations were performed for various uncertainty variable combinations using the batch MELCOR for convenience. (author)