Research On Criticality Analysis And Application Technology Of Nuclear Power Plant Safety-related Software

With the increasing scale and complexity of digital distributed control systems(DCS),how to understand the risks come with the complexity of the system has become a new issue.The criticality of software represents the necessity of limiting the software to acceptable risks.Therefore,the study of criticality analysis methods is of great significance for analyzing the risks come with the complexity of the system.Through criticality analysis,determine the corresponding strict development and verification requirements for each software(module),and treat software modules with different safety requirements differently,so as to reduce the development and verification costs of newly developed software,shorten the supply cycle of COTS software and reduce the cost of COTS software supply.With the advancement of technology,experts in functional safety related fields have proposed a great number of critical analysis methods for software and hardware systems,such as risk matrices,probability calculations,and criticality level screening etc.Software criticality analysis is the classification of the combined effects(i.e.,risks)of each failure mode and its probability of occurrence.In this study,on the base of method investigation,firstly,the criticality analysis of newly developed software in nuclear power plants(NPPs)safety-critical control software and COTS software of potential applications were carried out.Then,according to the characteristics of newlydeveloped software and COTS software,a software criticality analysis method based on functional module evaluation is proposed to meet the criticality analysis of newly developed software and COTS software at the same time.This method first performs criticality screening of the required functional modules of the system,and then verifies it through the Hazard and Operability Analysis(HAZOP).It combines the advantages of both newly developed software and COTS software criticality analysis methods,and reduces the high information Permission requirements avoid the need to establish fault trees for complex systems,and have wider applicability under the premise of ensuring the quality of analysis.Taking the safety-critical control software under the triple modular redundancy(TMR)safety-level DCS platform as the research object,the target safety integrity level(SIL)of each software module of the control software was determined through criticality analysis,Verifies the feasibility and effectiveness of the software criticality analysis method based on the evaluation of functional modules.It is proved that this method can simultaneously realize the criticality analysis of newly-developed software and COTS software under the condition of low information authority requirements.