Rigorous derivation of interfacing system LOCA frequency formulas for probabilistic safety assessment of nuclear power plants

Abstract

Determining interfacing system loss of coolant accident (ISLOCA) frequency is important from a public safety viewpoint. With the recognition that the conventional ISLOCA frequency formulas are rooted in approximations and derived with the integration of approximations, this paper provides general ISLOCA frequency formulas that are firmly rooted in mathematical definitions and derived more rigorously. The conventional formulas are shown to be special cases of the presented newly derived general formulas when the product of each of the failure rates and the mission time is sufficiently small. A numerical comparison between the conventional and general formulas with a case study is provided. The general formulas derived in this paper provide higher assurance on the conventional formulas that are widely used in the practice of probabilistic safety assessments of nuclear power plants.