Adoption of the Phenomena Identification and Ranking Table (PIRT) Methodology for Safety Assessment of a 1 GWe Stellarator Fusion Power Plant

The safety assessment of fusion power plants has historically relied on methodologies originally developed for fission reactors, with adaptations to address fusion-specific phenomena. However, a systematic and traceable methodology to identify and prioritize physical processes influencing plant safety has not yet been established in the fusion domain. In this work, we present the first application and formal adoption of the Phenomena Identification and Ranking Table (PIRT) methodology to the safety assessment of a 1 GWe stellarator fusion power plant (Chartreuse-P reactor). Building on the fission safety experience summarized by IAEA-FIP/P3-20 and OECD/NEA's best-estimate and uncertainty frameworks, our study develops a fusion-adapted PIRT framework that integrates with model-based systems engineering (MBSE) and digital safety environments. The methodology enables structured expert elicitation, scenario-driven ranking of thermal-hydraulic, magnetohydrodynamic, tritium transport, and structural integrity phenomena, and their mapping to system functions and safety criteria. The resulting Fusion PIRT matrix serves as a foundation for experimental planning, model validation, and code development-bridging safety demonstration requirements with digital verification workflows. Its implementation within the Chartreuse-P safety program supports the French regulatory process, including the Dossier d'Options de Sûreté (DOS) and proposes a case study for future regulatory licensing of stellarator facilities under ASNR guidance. This paper therefore establishes PIRT as a cornerstone methodology for fusion reliability and risk assessment, promoting traceability, transparency, and prioritization of safety-critical research activities within next-generation fusion power plant programs.

Keywords: PIRT, Fusion Safety, Stellarator, Safety Assessment, Phenomena Ranking, Reliability.