Modeling common-cause failures using stochastic hybrid systems

Abstract

In this paper, we develop a novel Common-Cause Failure (CCF) model for reliability assessment, based on component degradation information. A Stochastic Hybrid Systems (SHS) model is developed to describe the components and system degradation process by state dynamics, under CCFs. A component failure is either caused by cumulative degradation of the component or by destructive external events (shared root causes of CCFs). A case study is considered regarding the Auxiliary Feedwater Pumps (AFPs) of a Nuclear Power Plant (NPP) suffering internal flooding. AFPs may fail due to internal flooding from three main water sources, i.e. service water (SW), circulating water (CW) and fire protection water (FPW). A flood barrier is built to protect the AFP from internal flooding. System's fault tree is presented in Figure 1. Two CCFs are considered in this paper, as illustrated in Table 1. The developed SHS model is graphically illustrated in Figure 2. In the developed model, degradations of the components are characterized by stochastic differential equations: