Research On Dynamic Analysis Methods Based On Simulation Technology For Nuclear Power Plant Digital Instrument And Control System

Digital distributed instrumentation and control system(DCS)is critical to the safety of nuclear power plants(NPPs).With the introduction of DCS,an important issue is how to analyze and ensure the quality of DCS.Neither static analysis methods developed from previous analog instrument control nor traditional engineering experience can be fully applicable to DCS due to its enhanced dynamic interactions and complex structure of hardware/software/firmware.The enhanced dynamic interactions of DCS including both sequence and timing factors bring about two problems in the method to improve DCS quality: one is that the traditional risk analysis method can not fully describe two kinds of dynamic interactions of complex DCS system in the design and review of DCS,and the other is that how to effectively verify and validate complex dynamic system in design and validation of DCS.In this case,numerous researcheres proceed on developing the dynamic analysis method for complex DCS system,while no strategy is widely accepted currently for the limitation of modeling ability,amount of calculation and feasibility.NPP simulation technology can simulate the dynamic interactions of DCS and it is easy to integrate with DCS since they are both based on the digital technology.Therefore,in this study,we explored the DCS dynamic analysis method based on simulation technology and put forward the dynamic reliability analysis method and dynamic verification and validation(V&V)methodology to support the quality assurance of DCS.A DCS analysis simulation platform is developed and improved which is used to support the subsequent dynamic analysis methods of DCS.The simulation scheduling function is reconstructed for the large scale and continuous automatic start and stop simulation task.An equipment module are developed and supplemented to meet the need of DCS analysis.Coupling method of parallel running simulation code is studied to realize the high precision,real-time and stable simulation for the large-scale simulation by means of system splitting,parallel calculation and explicit coupling with the support of efficient real-time database.Models of NPP main systems are developed and verified under various operating conditions.Finally,a DCS-analysis simulation platform is obtained including large scope simulation models.The REST method is proposed for dynamic reliability analysis of complicated control system based on simulation technology.The dynamic failure mode and effect analysis(FMEA)method based on real DCS hardware and software is developed which can reveal the dynamic failure paths and failure modes which can not be analyzed by static FMEA.Dynamic FMEA plays an important role in supporting the establishment of the dynamic fault tree/event tree(FT/ET)and the analysis of failure modes,which reduces the dependency on the analyst's experience.SeGen,an automatic generation code for dynamic event trees,is developed employing the concept of sequence criticality and helps to sort event sequences according to their hazard.At the same time,a simulation exploration algorithm is proposed to guide the simulation of event sequence in the way of dichotomy according to the criticality of event sequence.The algorithm reduces the amount of calculation exponentially and improves the feasibility of REST method.The REST method is verified by its application in evaluating the reliability of the main feedwater control system(MFCS).It is proved that the REST method can simulate two kinds of interactions of DCS,at the same time,the calculation is feasible.The REST method maintains a similar structure of FT/ET that allows the sensitivity analysis and importance analysis,etc.,and makes it easy to be integrated with traditional NPP PSA models.Dynamic V&V methodology based on simulation technology is studied in this paper to guide the dynamic V&V of complex control logic as well as its hardware and software realization of DCS.Dynamic V&V methodology contains the overall structure design and the specific V&V methods for different kinds of DCS systems.First,the overall structure design for dynamic V&V of DCS is proposed according to the characteristic and requirement in different stages.Then the diversified simulation of DCS is realized and the integration methods between DCS and DCS-testing platform are studied for each simulation manner,which provide the technology support for the dynamic V&V methods.According to the V&V requirements and characteristics of different DCS systems,the dynamic V&V methods are summarized into four categories: 1)signal injection open-loop V&V method,2)integrated automatic comparison open-loop V&V method,3)direct online closed-loop V&V method,and 4)comparative closed-loop V&V method.These four dynamic V&V methods are similar to the four basic coordinate elements in the world of DCS dynamic V&V.They can cover the V&V of various types of DCS systems through its flexible combination and extended application.The dynamic V&V methodology proposed in this study has been widely applied in the V&V of both control systems and protection systems in NPP and help the testing personnel find DCS flaws in logic scheme,the configuration design,the field termination and the range conversion,etc.It is proved that the dynamic V&V methodology can increase the V&V efficiency of DCS significantly.The REST dynamic reliability analysis method takes advantage of the simulation exploration algorithms to reduce the load of simulation exploration exponentially,which makes it possible to consider multivariable dimensions of complex DCS system in dynamic reliability analysis.The dynamic V&V methodology for DCS guides V&V activities in various stages and covers the dynamic V&V of all types of DCS systems,which effectively improves the efficiency and reliability of V&V of NPP DCS.The two dynamic analysis methods provide feasible solution for the insufficiency in dynamic characteristics analysis in the quality assurance of complex DCS systems.