Implementing Probabilistic Component Design Methods in Plant Systems Design

An ASME Plant Systems Design (PSD-1) standard is being developed for design of facilities with potential for significant hazards to the health and safety of the public, the worker, and the environment. The standard includes requirements and guidance for design organizations to incorporate risk informed probabilistic design methodologies with traditional deterministic design methods, using reliability and availability targets. Previous papers have described the overall approach of PSD-1, where the plant systems and structures overall design is developed using appropriate probabilistic methods and then followed by component level design. This paper describes the component level design approach and the structure of the PSD-1 requirements and guidance. The steps include defining the component boundaries, assessing where a probabilistic method is appropriate, defining failure modes and mechanisms, defining mechanistic models, selecting appropriate probabilistic analysis methods, and performing the probabilistic analysis. The selected probabilistic models can depend on the availability of input data, the resolution of the model, and the computational cost for the analysis. The outcome of the probabilistic analysis for the component is fed back into the system and structures level analysis to verify that the system and structure level reliability and availability targets are met. If not met, the analysis may be repeated with changes to the system and structure design so the targets can be met. The process is demonstrated using an example of a steam generator with reliability and availability targets based on the system and structure design assessment.