Integrating RAMI into risk-informed decision-making for nuclear facilities

Operation of nuclear facilities requires the highest standards of risk management, where safety-related decisions must be rigorously justified, transparent, and auditable. However, the risk measures applied in decision-making for complex nuclear systems and processes are inherently heterogeneous and subject to uncertainty. Moreover, the long-term operation of the nuclear facilities must ensure economic viability at an acceptable level, which should be integrated into the decision-making process without compromising safety. Therefore, non-routine decisions concerning nuclear facilities typically extend beyond deterministic and probabilistic safety studies. They may involve additional factors such as economic indicators, security aspects, and societal concerns. Addressing such a broad range of issues requires a complex multi-attribute decision-making procedure. In response to this need, the Integrated Risk-Informed Decision-Making (IRIDM) framework was developed by the International Atomic Energy Agency. IRIDM provides a structured approach in which diverse aspects (deterministic and probabilistic safety assessment, standards and good practices, operational experience, human and organizational issues, security aspects, and socio-economic factors), represented by different risk metrics, are systematically evaluated and integrated into the risk-informed decision-making process. This work aims to extend the IRIDM framework by incorporating lifetime characteristics of the Reliability, Availability, Maintainability, and Inspectability (RAMI). Complementing the conventional Probabilistic Safety Assessment (PSA), which quantifies the accident scenarios leading to core damage and radiological releases, the integration of RAMI parameters provides broader insights into the probabilistic aspects. It captures scenarios that increase the forced outage rate without directly challenging safety and are therefore not addressed in PSA. The integration of RAMI into the IRIDM framework is presented and discussed in the context of real decision-making processes on the MARIA research reactor, operated by the Polish National Centre for Nuclear Research. The concept proposed herein is, however, broadly applicable within the nuclear industry to improve risk management processes.

Keywords: IRIDM, IRISC, IRDA, RAMI, MARIA.