Reliability based inspections of safety systems in NPP

An approach is proposed for the use of results of level 1 PSA for safety decisions with respect to inspections in NPP. The approach uses risk indicators. The indicators combine probabilistic importance measures of basic events which are defined in PSA. As a first step of the approach risk indicators of basic events are considered. However an inspection generally comprises several basic events. Thus risk importance of inspections will depend on combinations of several risk indicators of basic events. As for the first step risk indicators are of a more general meaning for risk-based decisionmaking. The concept of the first step is described in these paper. Application of combinations of several risk indicators is subject to further development. Examples are given in this paper for the use of each type of risk indicators at system function level. However, to point out risk importance of basic events risk indicators should be applied at each of the different levels of PSA. Some specific aspects are delineated in this paper for their application at accident sequence as well as hazard state level.