Incorporating MACST Mitigation Strategies into PSA Models: HRA and Data Issues

The Fukushima accident indicates, among others, that flexible and diverse mitigation strategies are needed to cope with a variety of unforeseen accident conditions that may be brought about by occurrence of beyond design basis accidents (BDBAs). These mitigation strategies will be typically implemented in Phase 2 or 3 when the evolving accident cannot be properly coped with by use of installed equipment alone. In this paper, we discuss the issues associated with crediting MACST equipment and relevant mitigation strategies in Probabilistic Safety Assessment (PSA), focusing on Human Reliability Analysis (HRA) and data issues. There are a number of issues that need to be addressed in order to properly credit portable equipment and relevant mitigation strategies in PSA. The research performed by EPRI, NEI and PWROG in this regard sheds light on these issues, providing some interim solutions. In this paper we discussed a couple of prominent issues, namely HRA issues and data issues. Provide that more details become available regarding procedures for portable equipment and failure data for such equipment are compiled, these issues could be addressed more appropriately, enabling more realistic estimation of the plant risk with credit for portable equipment in accident scenarios for which they provide an alternate success path.