Application of probabilistic safety assessment to parameters of operational limits and conditions of the opal research reactor

Abstract

This paper gives a brief explanation of Probabilistic Safety Assessment (PSA), the meaning and application of Operational Limits and Conditions (OL&Cs) for facilities and describes the application of PSA to the derivation of OL&C parameters such as Completion Times. ANSTO’s Research Reactor OPAL is used as a case study but the authors conclude that the methodology, based on NUREG/CR-6141, could equally be applied to major hazard facilities.

The PSA indicates that the OPAL reactor meets the regulatory safety limits and safety objectives. The very low risk is achieved by important design characteristics such as the two independent and diverse shutdown systems, minimal dependence on support systems for the safety functions, the absence of in-core experiments, and the redundancy in cooling modes.

Completion times are derived for safety systems and some sub-systems by balancing the incremental risk of single outages of those systems, and also by balancing the incremental risks associated with the expected number of outages of those systems and subsystems while ensuring that the incremental risks are tolerable.

This methodology can give an estimate of the total incremental risk of allowable outages of safety systems and subsystems taking into account the expected number of outages of those systems each year. An assessment of the tolerability of that additional risk can be made.

Keywords:

• Probabilistic safety assessment
• quantifi ed risk assessment
• applications
• operational limits and conditions
• risk-based decision making.

Additional information

Notes on contributors

S J Bastin

Simon Bastin holds a BE Mechanical from The University of Sydney and a MEngSc from the University of NSW. He has over 24 years of engineering experience including 20 years' specialising in risk and reliability engineering. Simon is currently the Manager of Systems Safety and Reliability at the Australian Nuclear Science and Technology Organisation (ANSTO) in Sydney.

J Perera

Joy Perera holds a BScEng degree from University of Ceylon, Sri Lanka and a MEngSc degree from the University of NSW. He has an electrical power engineering background and joined Australian Nuclear Science and Technology Organisation (ANSTO) in 1992 as a Safety and Reliability Analyst. Over the past 15 years Joy has been involved in many varied safety and reliability analysis tasks including the reviews of probabilistic safety assessments of ANSTO's nuclear reactors HIFAR and OPAL. Joy is currently a Safety and Reliability Adviser in ANSTO.