Study on Different Ways for Selecting NPP Design Extension Conditions

Abstract

With the further improvement of the safety requirements, the Design Extension Conditions need to be fully considered as an important design requirement in the design of advanced nuclear power plants. For Chinese new nuclear power plants and future new reactor types, in principle, a set of Design Extension Conditions must be obtained on the basis of engineering judgment, determinism and probability theory evaluation to further improve the safety of nuclear power plants. In current practice, PSA methods and models are often used to identify and determine extremely unlikely events and multiple failure events in the selection of the Design Extension Condition sequence list, while considering the design extended conditions given by determinism and engineering judgment. However, even with the same frequency screening values, the way in which the PSA model is used can be different, so it is necessary to study the effect of different ways on the results of DEC selection. In this paper, combined with the determination process of the DEC-A list of a third-generation reactor type, two different ways of identifying the DEC-A event sequences based on the PSA event sequence and based on the cutset-importance, are described, and the results are compared and discussed.