核电厂数字化仪控系统动态流程图方法分析研究

Research on Dynamic Flow Graph Methodology of Digital Instrumentation and Control System for Nuclear Power Plant

传统静态故障树方法对数字化仪控系统(DCS)的可靠性评价存在较大局限性,尤其是对包含动态特性和反馈信号的控制系统。作为新型概率安全分析方法的动态流程图法(DFM)具有动态特性,可表征系统变量和时间的关系、模拟逻辑信号控制,能够综合分析评价软件失效、硬件失效以及外部环境对系统可靠性的影响。本文选取CNP1000稳压器压力控制系统作为分析对象,假设发生稳压器高压信号缓解失效事件;分别应用DFM机制和故障树机制对其进行PSA建模分析,计算得到各自顶事件的发生概率、质蕴含与最小割集。最后通过两种模型结果的对比,总结分析出DFM方法较传统故障树方法的优势之处。

The conventional Fault-Tree approach has been widely used in the analysis of NPPs PSA, however it has a great disadvantage on analyzing the reliability of Digital Control System （DCS）, especially for the dynamic system and logic loops. As a new probability safety analysis method, due to its dynamic property, Dynamic Flow graph Methodology （DFM） can model the relationship between time sequence and system variables. Moreover, DFM can be used to analyze the impact of software failure, hardware failure and external environment, which are closely related to the reliability of system. In this paper, we research on the pressurizer pressure control system of CNP1000 NPPs and suppose an accident, in which we fail to control the high pressure of the pressurizer. Meanwhile, in this case, DFM and fault tree methodology are both used to conduct the PSA for this postulated top event by calculating the probability of top event and finding out the prime implicants/minimum cutset. After modeling and calculating by the two different ways, the theory and application of DFM have been mastered. Finally, through the comparison between DFM and Fault-Tree model results, it is indeed the case that we have concluded advantages of DFM over the conventional Fault-Tree approach.