Recommendations for Design-Stage Safety and Security Probabilistic Risk Assessment Co-Development

As many advanced and small modular reactor developers are entering the licensing process and seeking to expand their commercial offerings internationally, nuclear security is a critical but often overlooked element in the design process.Probabilistic risk assessments (PRAs) are being used to support risk-informed safety assessments but have not gained significant awareness as highly effective multi-purpose tools for a broad range of nuclear security applications.Designing a plant protection system and other barriers that might serve a security function after a conceptual or basic design phase may lead to higher total security costs and/or redesign of other buildings, structures, and system placements or components.This motivates a "security-by-design" approach.PRAs can supplement this approach by aiding in identifying and quantifying the risk importance of various target sets and assessing the impact or consequences of security scenarios, thereby improving the protection strategy to adequately address the risks due to all design basis threats.However, there are many fundamental differences between a PRA used for safety and one used for security events (i.e., sabotage events).When these differences are identified and included in the development processes, a coupled safety and security PRA can be effectively constructed without placing significantly more burden on the design and analysis teams.Using traditional PRA elements as a guide, this paper provides technical recommendations for the integration of security and plant protection features into a safety PRA, which can easily be turned on or off depending on the application.The goal is to create an effective and integrated safety and security PRA model without having separate models, thereby eliminating version control and consistency problems to which design phase risk assessments are vulnerable.1.