Fire Probabilistic Risk Assessment and its Applications in the Nuclear Power Industry

Advancement of fire risk analysis methods has resulted in widespread development of detailed fire probabilistic risk assessments (PRA) at nuclear power plants. The PRA models are maintained and frequently exercised to help ensure safe, reliable, and cost-effective operation of nuclear power plants. Quantitative risk metrics and criteria have been established for total plant risk (for example less than 10−4 per year total plant core damage frequency across all hazards) and change in risk associated with proposed plant changes (for example less than 10−6 per year increase in core damage frequency), and these quantitative metrics are used to support risk-informed decision-making. A brief overview of fire PRA and its applications is provided, with the intended audience being the general fire protection community who may not be familiar with the risk analysis methods and applications used by the nuclear power industry. At a high level, the fire PRA process can be organized into three tasks: fire scenario definition, plant response model development, and quantification. The fire PRA process is performed iteratively, with increasing levels of modeling realism commensurate with risk significance. At the end of the process, the PRA includes conservative modeling of low risk fire scenarios, very detailed modeling (and understanding) of the most risk significant scenarios, and a sliding scale of modeling detail for scenarios of intermediate risk significance. These analyses have provided meaningful qualitative and quantitative insights that are readily used for the identification and management of risk. Fire PRA has achieved sufficient credibility and value within the nuclear industry that the United States federal regulation was amended to allow implementation of the risk-informed, performance-based fire protection standard NFPA 805 as an alternative to the traditionally prescriptive fire protection requirements.