Current trends in Risk-Informed changes to Limiting Conditions for Operation

Abstract

Among the applications of the Probabilistic Safety Analysis (PSA) for analysing safety related issues at Nuclear Power Plants (NPP) one can find the use of the PSA to support the risk-informed analysis of changes to Technical Specification (TS) as a very important application area. Thus, the early 80’s saw the development of methodologies based on probabilistic methods to analysis the impact on the risk level of the changes to the Allowed Outage Times (AOT) and Surveillance Test intervals (STI), which are included in the Limiting Conditions for Operation (LCO) and in the Surveillance Requirements (SR) respectively, which, in turn, are part of the plant Technical Specifications (TS). As probabilistic information provided by the PSA was the first to be considered, these applications were referred to as risk-based analysis of changes to AOT and STI in TS (RBTS). The middle 90’s saw the growth of a new trend towards the addition of deterministic information to PSA applications to support the integrated (deterministic and probabilistic) analysis of the changes to both requirements, yielding to the use of the PSA in the so called risk-informed analysis of changes to AOT and STI in TS (RITS) [1, 2].