NAPS PSA application allowed outage time optimisation

PSA provides an integrated model of the overall safety of the plant, which puts the safety issues in perspective, and helps in safety decisions related to both design and operations. NAPS Level-l PSA has been completed with the objective of presenting an integrated picture of safety of the NAPS which encompasses design, operational practices, component reliability, dependencies and human reliability. This has helped in understanding the weak links and plant vulnerabilities and the strengths in design and operational practices. There is always a desire to optimize the technical competency, resources and to operate the plant in most efficient practicable manner. In recent years, the operation of Indian Nuclear Power Plants has been characterized by improved availability/capacity factors and reduced forced outages. NAPS Technical Specification for operation has been revised in the year 2009. NAPS PSA level-1 was extensively used as an engineering tool for Risk Informed Decision making for optimization of Station Technical Specifications with regard to Allowed Outage Time (AOT) and Surveillance Test Intervals (STIs). The approach outlined in USNRC RG-1.174 [5] andRG-1.177 [6] has been used as a guideline for optimization of Allowed Outage Time taking into consideration Instantaneous (conditional) risk, Cumulative Risk over the allowed outage time period, and the average risk over a long period. This paper outlines the approaches followed for the revision of AOTs in station technical specification. The paper also covers the acceptance criteria for the assessment of the submittals on technical specification change proposals. The illustrative clauses, where application of this methodology for technical specification optimization are presented.