基于RISMC方法的非能动核电厂小破口事故风险重要序列分析

Pilot Application of the RISMC Methodology on Specific SBLOCA Sequences of Passive NPP

文章以典型非能动核电厂小破口失水事故为研究对象,基于风险指引的安全裕度特性分析方法(Risk-Informed Safety Margin Characterization,RISMC),耦合确定论和概率论方法对事故发展进程进行研究,选取特定风险重要序列进行精细化建模分析,对重要系统进行离散分支(如自动卸压系统),对重要不确定性参数进行抽样处理(如自动卸压系统阀门阻力、内置换料水箱阀门阻力)。修改原概率安全分析模型中较为保守的成功准则概念,建立改进的离散事件树,以系统成功列数为依据建立故障树。针对特定序列进行不确定性参数的抽样并且对每一组工况进行全厂事故仿真模拟。从而,得到每个序列发生的频率以及在该特定条件下的条件失效概率,最终得到基于RISMC方法的堆芯损伤频率值。分析主要针对自动卸压系统配置和敏感性进行,运用基于RISMC方法CARS软件的分析计算,发现各序列的CDF值均有一定程度的减小。文章基于RISMC的案例分析验证了该方法在非能动电厂安全分析中的可行性,也证明该方法能够去掉一些过保守性,更加现实地对事故风险进行评估,有利于更准确地认识核电厂的安全裕量。

The RISMC methodology is an advanced safety analysis method in nuclear power plant.It aims at coupling of the DSA method and the PSA method.In this paper,a typical small break LOCA of a passive nuclear power plant is taken as the case of study,expecting to get more realistic risk insights using RISMC methods.Based on the theory of the Risk Informed Safety Margin Characterization methodology,the development process of the accident is studied.The specific sequence is selected to be studied.The important systems are discretely branched(such as the Automatic Depressurization System),and the important uncertainty parameters are sampled(such as the ADS valve and the IRWST valve resistance coefficient).The event tree is re-established,and the success criterion of the head is modified.The fault tree is re-established.After that the uncertainty parameters are sampled for specific sequences and the accident simulation of the whole plant is carried out for each condition.Thus,the frequency of each sequence and the conditional failure probability under the specific condition are obtained,and the core damage frequency(CDF)value based on the RISMC method is finally calculated.Through the analysis and calculation of the RISMC method,it is concluded that the calculated value of the CDFin each selected sequence is reduced to a certain extent.This paper verifies the feasibility of the RISMC method in application on passive nuclear power plants,and also proves that the method can remove unnecessary conservatism.More realistic assessment of the risk helps us quantify the safety margin of nuclear power plants better.