Shutdown Probabilistic Safety Assessment - A Case Study for the Pressurized Water Reactor

Shutdown probabilistic safety assessment may be considered as an extension of power probabilistic safety assessment applied to the shutdown conditions of the nuclear power plant. It is more complex in sense of variety of models, because the plant shutdown is a sequence of plant operating states, which differ among each other so much that the probabilistic safety assessment models, which represent them, need to be varied in order to represent them realistically. The method is developed, which follows mostly the steps known in power probabilistic safety assessment with an exception of definition of plant operating states, which are defined in a way that one plant operating state suits its respective specific probabilistic safety assessment model. The number of plant operating states has to be large enough to consider the differences between them in sense of the related plant parameters and configurations of the plant equipment. At the same time, the number of plant operating states has to be small enough, in order that the number of the probabilistic safety assessment models representing them is small enough for the performance and cost effectiveness of the related work. The results of a case study based on a two loop nuclear power plant with the pressurized water reactor are presented and discussed. The results show that the risk of different plant operating states varies significantly and is in average lower than the risk of the plant in full power operation.