Study for Reliability Analysis of Operator Response Process Under IBLOCA Accident in Nuclear Power Plant

The reliability of the operator's response process after a nuclear power plant accident has an important impact on the overall reliability of accident mitigation. The automatic diagnostic function of nuclear power plant state is designed for the advanced digital control system, by monitoring and processing the plant, it provides an initial orientation or reorientation diagnosis for the Emergency Operating Procedures (EOPs) during emergency operating conditions. Therefore, the operator response process in main control room, especially the potential human errors have some new characteristics, when compared with the traditional way. The qualitative assessment of the operator response process forms the basis for the quantification of the associated Human Error Probability (HEP). The purpose of this paper is to study the reliability of the operator actions required to establish simultaneous Hot Leg injection following an Intermediate Break Loss of Coolant Accident (IBLOCA), a typical accident condition of nuclear power plant. The accident sequence and operator's actions are given, the detail qualitative and quantitative assessment are implemented base on the foundation of SPAR-H method by a constructed fault tree. The result shows that the failure probability of operating from the Auxiliary Control Panel (ACP) is higher than operating from the Plant Computer Information & Control System (PCICS). The main recommendations are providing more training for operation from the ACP following a loss of PCICS, increase descriptive information within the EOPs and the Human Machine Interface (HMI), providing a dedicated plant status display system and then decrease the reliance placed on the knowledge and memory of the operators to understand important information about plant configuration. The reliability assessment helpful to improve the human factor suitability, provide guidance for optimize the operator's response process and effectively improve the reliability of engineering design under an IBLOCA accident scenario.