辅助给水系统的重要作用是带出反应堆冷却剂系统余热,在三里岛事故后对辅助给水系统的改进及其对核电厂事故的缓解作用受到了关注。为了提高核电厂的整体安全和系统可靠性,福清核电一期工程对核电厂专设安全设施辅助给水系统(ASG)进行设计改进。本文采用概率安全分析的方法构建了系统改进前/后ASG系统的故障树模型,对系统可靠性进行分析,采用β因子模型法对部件共因失效进行定量分析,并对故障树的割集进行计算,表明改进后ASGP0200和ASGP0300两个关键顶事件发生概率都显著减小,汽动泵列的最小割集发生概率占顶事件发生概率也显著降低。同时,针对与ASG系统相关始发事件建立事件树模型,考虑核电厂功率运行工况,ASG系统改进前/后对核电厂堆芯损伤频率(CDF)的贡献以及始发事件组对CDF的贡献百分比进行了计算,结果表明,ASG系统改进后,降低了核电厂的CDF,使核电厂安全获得改善。

The principal role of the Auxiliary Feedwater System(ASG) is to support the removal of stored and decayed heat from the Reactor Coolant System (RCS). After the Three Mile Island (TMI) accident, the ASG modification for the mitigation of the accidents of the nuclear power plants (NPPs) becomes a research issue. In order to improve the overall safety of nuclear power plants (NPP) and the system reliability, the ASG is renovated with the improved safety facility (ESF) for the Fuqing NPP. A fault tree (FT) model of the ASG before/after the improvement is built by the Probabilistic Safety Analysis (PSA) to analyze the system reliability. The β factor model is used to quantitatively analyze the failures of the components and the minimal cutsets of the FT are calculated. The results show that the probability of the ASGP0200 and the ASGP0300 as the top key event is significantly reduced; and the percentage of the turbine driven pump minimal cutset probability in the top key event probability is also significantly reduced. The initial event tree (ET) model related to the ASG before/after the improvement is built to analyze the contribution of the improvement on the CDF under the power operation condition. The percentage of the initial event contribution on the CDF before/after the ASG improvement is also investigated. The results show that because of the ASG design improvements, the CDF of the NPP is decreased, which means that the safety of the NPP is improved.