Study for Human Reliability Analysis on Emergency Feedwater Injection Under Severe Accident in Nuclear Power Plant

Abstract

AbstractThe reliability of the operator's response process in severe accident has an important impact on the overall reliability of large release frequency mitigation. Severe accident involve a complex diagnostic process that need weighing the pros and cons carefully before making final decisions. Such decisions are likely to have negative effects, such as while preventing the progress of the accident in some aspects, but also aggravating others, either intentionally or unintentionally. At the same time, severe accident also involve more complex plant emergency organization, technical support organization and accident evolution mechanism than design basis accident. However, due to the lack of a clear and suitable severe accident procedure, the study on operator's response process and its reliability are relatively insufficient, unable to effectively find the weak links in operators, procedure, organizations and other influencing factors, and make targeted improvements of human reliability in SA situation are very difficult. The purpose of this paper is to study the reliability of the operator actions required to establish Emergency Feedwater (EFW) injection following reactor core damage, a typical severe accident condition of nuclear power plant. The EFW injection are described by task analysis and subject to qualitative and quantitative assessment of the safety significant potential errors and associated Performance Shaping Factors base on the foundation of SPAR-H method. A Human Error Probability of 6.11E-01(Pwd) is derived, the result shows that there is little margin for error recovery due to the short timescales in which the response is required by the operators and technical support teams. The main recommendations are providing more training for operators and technical support teams to ensuring the crew has adequate situational awareness before diagnoses or decision-making are required. The SAMGs should provide clear guidance and instructions for regular, periodic checking of key plant parameters critical to mitigating a severe accident. A wide range and narrow range value comparison of the steam generator level need to provide to support timely diagnosis. Consideration should be given to designing the SAMG initial response such that EFW injection is always diagnosed and performed by the MCR crew following SADV failure, with Technical Support Team (TST) providing support if operational. This ensures that the task can be progressed quickly following SADV failure and removes the need for handover and allowing the TST to obtain situational awareness. The task analysis and 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 a severe accident scenario.KeywordsSevere accidentEFW injectionHuman reliability analysisPerformance shaping factorsSevere accident management guidelinePlant emergency organizationTechnical support team