The extended living probabilistic safety assessment

The term living probabilistic safety assessment was defined soon after the initial probabilistic safety assessments were implemented. The objective of this article is to present the extended living probabilistic safety assessment and its applications considering realistic nuclear power plant models, including the low power and shutdown plant operating states. One of the key objectives is to compare the suitability of conventional and additional risk measures, core damage frequency and conditional core damage frequency, respectively. The methods are presented considering all states of the plant from the full power operation to the low power and shutdown states. The example models of the nuclear power plants and the results of the living probabilistic safety assessment of the plant operating states are discussed. The results show that the risk of low power and shutdown states is generally smaller than the risk of full power operation, but the low power and shutdown plant operating states differ significantly among each other regarding the risk level. The deficiency of living probabilistic safety assessment applied to the plant shutdown states is connected with significantly increased human effort for the analyses, with a significantly greater amount of results and with increased uncertainty of some parameters due to the larger dynamics of actions in the plant shutdown versus the full power operation states. The benefit of the living probabilistic safety assessment applied to the plant low power and shutdown states lays in consideration of all states and potential identification of risk significant states and directions for possible safety improvements.