Application of Probabilistic Risk Assessment Approach in Nuclear Power and Space Sectors

Abstract

Probabilistic Risk/Safety Assessment (PRA/PSA) is a comprehensive, structured, logical and a quantitative analysis technique to identify and assess risks in complex technological systems, to improve their safety and performance in a cost-effective manner. PRA methods were developed in the US aerospace industry. The nuclear sector adopted PRA techniques widely in 1980s after the Three Mile Island (TMI) accident. Thereon, the technique has advanced into an important risk management tool and is mandated by nuclear regulatory authorities worldwide. PRA has helped to strengthen the regulatory policies on safety, enhance system engineering, evaluate cost-effective design options, improve accident mitigation procedures and much more. In space industry, the National Aeronautics and Space Administration (NASA) first used PRA in the operational phase of human space flight programs. Since its first comprehensive use post the Challenger Accident, it has been recognized as an effective method for assessing complex mission risks. Early integration of PRA with system and design engineering aided in increasing the reliability and availability of systems, crew safety and optimized lifecycle costs. PRA is now included as a requirement during the design phase of crewed space vehicles as well as for high priority robotic missions and other critical missions in the space sector. The paper provides an overview of the PRA practices in the nuclear and space sector, outlining the overall framework, objectives, definition of risk, regulations, standards and guidance for each sector. It compares the elements/tasks of nuclear and space PRA and addresses the limitations of a conventional PRA approach as well as the challenges in developing PRA models for space missions. The paper also highlights the significance of PRA and how it can be used as a useful risk management tool for space missions. The paper concludes by using the nuclear industry as an example to argue that PRA must be viewed as an essential requirement by space regulatory bodies to analyse the mission risk in a holistic manner.