Modification Of Human Reliability Analysis Using HCR Combination With THERP In Third Qinshan NPP PSA

The concept that human error is an important risk contributor in Nuclear Power Plant operation is commonly accepted and technics for human reliablity analysis are needed to understand, assess and quantify human errors and human error is one of the important aspects that must be considered in Probabilistic Safety Assessment.Post accident human error of single steam generator tube rupture and loss of out-site power in Third Qinshan Nuclear Power Plant is analysed using the methodology of Human Cognitive Reliability (HCR) , combination with Technic for Human Error Rate Prediction (THERP). Among actions needed be taken by operators, HCR is used to assess human errors ralating to diagnosis and THERP is used to assess human errors relating to post diagnosis actions. If the results are much better comparing with the one computed by Screening Analysis Approch, the methodology of HCR combination with THERP can be widely used in the future human reliability analysis.The results indicate that the post accident total human error rate of single steam generator tube rupture are 0.0279 and of loss of out-site power is 0.2474 in the Third Qinshan Nuclear Power Plant.At present the method used for human reliability analysis in Third Qinshan Nuclear Power Plant is Screening Analysis Approch, supposing that human error rate is completely dependent on the time available to accomplish the diagnosis and post diagnosis actions. The time available to accomplish diagnosis and post diagnosis actions originates from accident sequences in Final Safety Analysis Report.Because HEPs in PSA of Third Qinshan Nuclear Power Plant are completely dependent on time and have no reasonable reasons, in addition diagnosis and post diagnosis actions are not classified and Emergency Operating Procedures are not considered in event trees, the results are not very reliable. While all human actions are classified as skill-based, rule-based and knowledge-based behaviors in HCR model, and operators'training, pressure and man-machine interfaces are considered, so HCR can well assess human diagnosis and decision making errors associated with tasks restricted by time. THERP can well assess human executive errors and operators'pressures, dependence between human actions and other Performance Shaping Factors are considered. Generally speaking, human actions instructed by EOPs are processes which first diagnose and then execute, and diagnosis errors are modeled by HCR and post diagnosis actions are modeled by THERP, human errors can be assessed much more comprehensive and accurate. According to the analysis, the results are much better comparing with the one computed by Screening Analysis Approch, the methodology of HCR combination with THERP can be widely used in the future human reliability analysis in Third Qinshan Nuclear Power Plant.