%0 Journal Article
%T Risk-Based Allowed Outage Time and Surveillance Test Interval Extensions for Angra 1
%A Sonia M. Orlando Gibelli
%A P. F. Frutuoso e Melo
%A S¨Śrgio Q. Bogado Leite
%J Journal of Quality and Reliability Engineering
%D 2012
%R 10.1155/2012/176270
%X In this work, Probabilistic Safety Assessment (PSA) is used to evaluate Allowed Outage Times (AOT) and Surveillance Test Intervals (STI) extensions for three Angra 1 nuclear power plant safety systems. The interest in such an analysis lies on the fact that PSA comprises a risk-based tool for safety evaluation and has been increasingly applied to support both the regulatory and the operational decision-making processes. Regarding Angra 1, among other applications, PSA is meant to be an additional method that can be used by the utility to justify Technical Specification relaxation to the Brazilian regulatory body. The risk measure used in this work is the Core Damage Frequency, obtained from the Angra 1 Level 1 PSA study. AOT and STI extensions are evaluated for the Safety Injection, Service Water and Auxiliary Feedwater Systems using the SAPHIRE code. In order to compensate for the risk increase caused by the extensions, compensatory measures as (1) test of redundant train prior to entering maintenance and (2) staggered test strategy are proposed. Results have shown that the proposed AOT extensions are acceptable for two of the systems with the implementation of compensatory measures whereas STI extensions are acceptable for all three systems. 1. Introduction Traditionally, Technical Specifications (TS) such as limiting conditions of operation, which include system/component AOT and STI, have been established based only on deterministic analysis [1, 2] and engineering judgment [2]. However, the experience with plant operation indicates that some elements of the requirements may be unnecessarily restrictive, and a few may not be conducive to safety [2], stressing the need to review them based on probabilistic models capable of assessing the incremental risks associated with their modifications. In the last decades, PSAs have been elaborated and used not only to support risk-informed regulation but also to evaluate new plant designs, among other applications. Due to its broad modeling capability, which includes system functions and common-cause failure events (CCF), PSA is especially suitable for the analysis of TS modifications. Risk-based methods to improve TS requirements are meant to (1) evaluate the risk impact of TS modifications in such a way as to objectively justify them and (2) provide risk-based information for the regulatory decision-making process [1]. This work presents an evaluation of AOT and STI extensions for three Angra 1 safety systems [3] through the use of its PSA Level 1 study, namely (1) Safety Injection System (SIS), (2) Service
%U http://www.hindawi.com/journals/jqre/2012/176270/