Risk informed regulatory decision-making in assessment of changes in technical specifications

Probabilistic Safety Assessment (PSA) is increasingly being used in Nuclear Power Plants (NPPs) worldwide for assessment of core damage frequency, radioactivity release frequency to the environment and assessment of risk to the public. PSA methodology has matured over the years and is also finding applications in areas such as on-line risk monitoring and performing living PSA, Optimisation of Technical Specification, Risk Informed In-Service Inspection and Reliability Centered Maintenance. PSA provides a systematic approach for integrating the risk concept into safety assessment and regulatory decision-making. A worldwide consensus is emerging for the use of PSA as a complement to the deterministic analysis and in arriving at more balanced decision-making. This approach is normally referred to as 'Risk Informed' decision-making. PSA models should meet certain technical requirements for being useful in such applications and the quality of PSA should be consistent and commensurate with the intended application. Effective use of PSA results requires that comparison be made against a set of either established acceptance criteria or targets. In this paper, the technical requirements for adequacy of PSA for use in Risk Informed decision-making in different areas are presented. The methodology for application of PSA for technical specification optimisation is described. The acceptance criteria for the assessment of the submittals on technical specification change proposals are discussed. The illustrative example for application of this method of technical specification optimisation is presented. (author)