State of the art in reliability of thermal-hydraulic passive systems

In order to address the issues posed by the development of advanced nuclear technologies, this article endeavours to analyse the current state of the art in reliability of passive systems, for their extensive use in future nuclear power plants. Inclusion of failure modes and reliability estimates of passive components for all systems is recommended in probabilistic safety assessment (PSA) studies. This has aroused the need for the development and demonstration of consistent methodologies and approaches for their reliability evaluation, within the community of the nuclear safety research. This report provides the insights resulting from the survey on the technical issues associated with assessing the reliability of passive systems in the context of nuclear safety, regulatory practices and probabilistic safety analysis. Special emphasis is placed on the reliability of the systems based on thermal-hydraulics, for which methods are still in a developing phase. The main achievements of these studies are presented and a viable path towards the implementation of the research efforts is delineated as well.