Application of System-Theoretic Process Analysis (STPA) in Nuclear Instrumentation and Control systems

Abstract

This thesis evaluates the application of System-Theoretic Process Analysis (STPA) in analyzing the Instrumentation and Control (I\&C) systems within Nuclear Power Plants (NPPs). Ensuring the safety of I\&C systems is crucial, as they play an important role in NPPs' operations. Most I\&C systems in NPPs are reaching their end of life and require upgrades. These upgrades will replace the older analog electromechanical systems with newer software-intensive digital I\&C systems.

Traditional hazard analysis methods, such as Fault Tree Analysis (FTA) and Failure Modes and Effects Analysis (FMEA) are more suitable to be used when analyzing older analog electromechanical systems and they have limitations when applied to these newer digital I\&C systems.

System-Theoretic Accident Model and Processes (STAMP) is a new accident model based on the System Theory. STPA is a tool based on STAMP that can be used to analyze complex systems that consist of software.

This thesis uses a case study of a feedwater control system that is used to control the feedwater level inside the reactor pressure vessel of an NPP. The provided case study is analyzed using STPA and the results are presented in this thesis. In addition to the results of the STPA, the observations, and challenges throughout the process are discussed. The thesis also discusses the impact of the level of information used in conducting STPA.