The International Atomic Energy Agency (IAEA) launched Coordinated Research Project (CRP) I31033, “Advancing the State-of-Practice in Uncertainty and Sensitivity Methodologies for SA Analysis in Water-Cooled Reactors,” in 2019. One of the main outputs of this CRP was a series of technical documents (TECDOCs) presenting the methodologies for performing uncertainty and sensitivity analysis developed by each of the 22 participating institutions and applied to different water-cooled reactors, i.e., pressurized water reactors (including small modular reactors), boiling water reactors (BWRs), CANDUs, and VVERs, as well as the QUENCH-06 experiment.

This paper presents the BWR group´s main outcomes from this CRP and the contents of the TECDOC in preparation, including best practices and lessons learned by the four organizations contributing to the TECDOC: (1) CIEMAT (Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas), (2) GAEC (Ghana Atomic Energy Commission), (3) CNSNS (Comisión Nacional de Seguridad Nuclear y Salvaguardias), and (4) ININ (Instituto Nacional de Investigaciones Nucleares). 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 chose a short-term (unmitigated) station blackout scenario for analysis, and the scope of the analysis was limited to only in-vessel phenomena. In the case of CNSNS, depressurization and reactor core isolation cooling injection were considered mitigating measures, and the analysis included 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 the figures of merit and the set of uncertain code input variables with their associated probability density functions is also presented in this paper.