Dr. Mihai A. Diaconeasa of the PRA Group was awarded a U.S. Dept. of Energy Nuclear Safety Research and Development (NSR&D) Program grant for a collaborative project led by the Idaho National Laboratory on advancing multi-hazard risk and safety considerations for aging nuclear facilities.
Events such as the 2011 Fukushima Daiichi accident have highlighted the importance of considering the cascading impacts of multi-hazards for PRA. Moreover, many of the reactors in the current nuclear fleet in the U.S. are already operating well beyond their initially planned design life, and applications for further extensions to operating licenses are being considered. Therefore, considering multi-hazard effects and aging deterioration in the natural phenomena hazards probabilistic risk assessment process will contribute to the safety of both existing and future nuclear facilities.
This project will provide technical support to the Office of Nuclear Safety’s NSR&D Program in demonstrating a multi-hazard time-dependent PRA approach for nuclear facilities considering aging-related deterioration of structures. A generic pressurized water reactor (PWR) reactor subjected to seismic mainshock-aftershock sequences considering the aging of the containment structure will be used as a case study to demonstrate the multi-hazard PRA approach. Using advanced modeling and simulation, seismic mainshock-aftershock fragility functions will be simulated for the containment structure considering aging effects. A multi-hazard PRA model for a generic PWR reactor will be built to quantify the multi-hazard core damage frequency (CDF) and large early release frequency (LERF) with explicit time-dependent modeling of event sequences. To date, the cascading impacts of multi-hazards are not adequately accounted for in the PRA models for nuclear facilities. In addition, for both initial and periodic evaluation of facilities to withstand natural phenomena hazards, deterioration of the structures, systems, and components (SSCs) due to aging and other effects is not adequately considered. By advancing multi-hazard considerations accounting for aging effects, this project will contribute to improved understanding of the safety of aging nuclear facilities. Project outcomes such as the multi-hazard CDF and LERF will also allow facility owners to optimize upgrade and retrofit protocols.