STRATEGIES FOR MITIGATING RELEASES DURING A SEVERE ACCIDENT

摘要

In 2012, EPRI published "Investigation of Strategies for Mitigating Radiological Releases in Severe Accidents - BWR Mark I and Mark II Studies" (EPRI 1026539). This report assessed the value of various strategies starting from the perspective that there was a core vessel breech situation without regard for how the scenario progressed to that point. The objective was to identify strategies that could enhance containment performance. In the current study, EPRI performed a more comprehensive evaluation of the scenarios and how they developed. This allows for state-of-knowledge to be incorporated into the potential release scenarios. A focused scope level 3 Probabilistic Risk Assessment (PRA) was developed for Extended Loss of AC Power (ELAP) sequences to evaluate not only the releases from the various scenarios, but also the potential for offsite consequences. The analysis shows that near all consequence reduction can be achieved by providing a method for severe accident capable water addition to the containment in Mark I and Mark II plants. Any other strategy provides marginal additional benefit. In this study, EPRI used high powered computing (HPC) to explicitly transfer sequence knowledge through the analysis out to the consequence end states. More than 500 Modular Accident Analysis Program (MAAP5) simulations were run to characterize each mitigating strategy; and more than 12000 simulations in all were performed for the study. Methods were developed for generating the input for these simulations and presenting the output in a meaningful manner. A focus of this paper is on the presentation of output from such a large set of simulations in a meaningful manner. Some of the more useful ways of characterizing the output are presented.