Lessons Learned and Best Practices on BWR Severe Accident Uncertainty and Sensitivity Analysis in the Framework of the IAEA CRP I31033

Abstract

IAEA launched the CRP I31033 “Advancing the State-of-Practice in Uncertainty and Sensitivity Methodologies for Severe Accident Analysis in Water-Cooled Reactors” in 2019. One of the main outputs of this CRP is a series of TECDOC documents presenting the methodologies for performing uncertainty and sensitivity analysis developed by each of the 22 participant institutions and applied to different water-cooled reactors, i.e. PWR (including SMR), BWR, CANDU, and VVER, as well as to the QUENCH-06 experiment.

This paper presents the BWR group´s main outcomes from this CRP and the contents of the TECDOC document in preparation, including best practices and lessons learned by the 4 organizations contributing to the TECDOC: 1) CIEMAT, 2) GAEC, 3) CNSNS, and 4) ININ. The first two institutions addressed severe accident scenarios in a BWR/3 with Mark I primary containment, while the last two used models of a BWR/5 with Mark II containment. Except for CNSNS, the participants have chosen a short-term (unmitigated) Station Blackout scenario for analysis, and the scope of the analysis is limited to only in-vessel phenomena. In the case of CNSNS, depressurization and RCIC injection are considered mitigating measures, and the analysis includes both in-vessel and ex-vessel phenomena. The MELCOR code was used by the first three participants, and the MAAP5 code was used by ININ. Information on figures of merit and the set of uncertain code input variables with their associated probability density functions are also presented in this paper.