Integrated Reliability and Risk Assessments of Nuclear Facilities

Reliability is the probability that a system will perform its intended function satisfactorily during its lifetime under specified environmental and operating conditions. Risk can be measured by assessing the probability of an undesired event (e.g., a system failure) and the magnitude of its consequences. Therefore, risk and reliability are complementary variables. Licensing of nuclear facilities requires safety and risk assessment. Probability risk assessment implies carrying out a quantitative assessment of the reliability of items important to safety (IISs). In addition, reliability assessments are required during all lifetime phases for optimizing plant performance, maintainability and safety. Thus, the outcomes of reliability and risk assessments are interchangeable and complementary. This chapter proposes a framework for integrating reliability and risk assessments of IISs of nuclear facilities using tools of reliability engineering, as Markov models, fault tree analysis, event tree analysis, reliability block diagrams and life data analysis. Based on frequency-dose limits to the public, risk acceptance criteria are also suggested in the scope of the framework. A case study demonstrating the advantages of using the integrated approach applied to a preliminary plant design phase of a nuclear fuel fabrication, to meet risk acceptance criteria and licensing requirements, is presented.