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.