Coupling model checking and PRA for safety analysis of digital I&C systems

Digital instrumentation and control (I&C) systems play an important role in the operation of nuclear power plants (NPP). Due to many unique features of digital systems the safety and reliability analysis of such systems can be challenging. There are several methods used for analyzing the safety and reliability of digital systems in NPP with their strengths and weaknesses. In this paper, the focus is on model checking and fault tree analysis (FTA) in the context of probabilistic risk assessment (PRA). Model checking is a computer-aided verification method developed to formally verify the correct functioning of a system design model by examining all of its possible behaviors. Fault tree analysis is a top down approach used for failure analysis. In this paper the two approaches are presented and compared in the modelling of an example system and their benefits and limitations are discussed. The example system used with both approaches is a fictive boiling water reactor. Additionally, ways to couple these methods to enable more extensive or practical safety analysis of digital systems are proposed.