STPA-Based Hazard and Importance Analysis on NPP Safety I&C Systems Focusing on Human–System Interactions

Abstract

To ensure system safety, conducting required control actions (CAs) in time at the right place is essential. Among the CAs, safety critical ones such as reactor trip signals in a nuclear power plant are preferentially and automatically generated by the instrumentation and control (I&C) system. If necessary, however, they can also be generated manually by human operators. Even for manual CAs, though, the I&C system is still needed to convey relevant feedback to the human operators. It is therefore indispensable to analyze the risk associated with the transmission of feedback to the human operators in terms of the condition of the I&C system. In this context, System-Theoretic Process Analysis (STPA) can provide a framework to link the conditions of the I&C system with the feedback transmission for manual CA generation. Based on STPA, this study proposes a method to analyze I&C system hazards and assess the relative importance of system components in terms of human–system interactions, or more specifically, feedback transmission for manual CA generation. As a feasibility study, the method is applied to an example case requiring reactor trip signal generation in the Advanced Power Reactor 1400 (APR-1400).