Accident sequence evaluation of complex systems with multiple independent protective systems

This paper proposes a systematic evaluation of on-demand failure of protective systems. For a protective system to perform its function, the protective system must satisfy the following requirements: (1) the availability of the protective system, (2) the detection of a plant failure, and (3) the selection of an appropriate protective action, and (4) the performance of the specified protective action. If any one of the requirements is not satisfied, the protective system gets failed. Based on the accident occurrence probability, the improvement of maintenance policy and the re-design of independent protective systems can be considered. An illustrative example of a simple reactor system with several protective systems including operator actions shows the details of the proposed method.