Reliability analysis of passive systems: An overview, status and research expectations

Passive systems, operating on the principle of natural circulation, are adopted extensively in advanced and innovative nuclear reactor designs. Though passive systems are adjudged to be safe, simple and economical, they are often characterized by uncertainties. To ensure the effective and stable operation of these safety-based systems when deployed, it is important to evaluate their reliability using dependable methods. This work presents an extensive coverage of the research contributions to the thermal-hydraulic reliability of passive systems of simple configurations with the different approaches to passive systems reliability evaluation discussed. In addition, the technical issues in the key procedures for implementing thermal-hydraulic reliability methods which consist of systems characterization and reliability mathematical modelling, identification of influencing parameters, uncertainties quantification, sensitivity analysis and setting of failure criteria are extensively discussed. The drawbacks of the existing thermal-hydraulic reliability methods which serve as motivation for future research have been highlighted. The ways to resolve the issues associated with the highlighted procedures in thermal-hydraulic reliability analysis are proposed and efforts being made to improve on thermal-hydraulic reliability methods are discussed in detail. Furthermore, recommendations for further research necessary to ensure the development of robust and consistent thermal-hydraulic reliability methods are enumerated. This paper in its entirety thus serves as a synoptic guide to newcomers in reliability analysis, an up-to-date reference for researchers and also to set future research tracks in passive systems reliability.