Research On Nuclear Plant Digital Control System Reliability Evaluation Methodology

Nuclear power plant control system is the indispensable important component for plant safe operation. In the whole life cycle of the plant, it is charge to monitor and protect the station, and make it safe, stable, efficient operate. A safe and reliable control system, is not only brought about by the economic benefits, there is a huge social benefit (only the safe and stable operation of the nuclear power plant will be public recognition). In recent years, along with the digital technology has been widely used in nuclear power plant control, digital control system has become the mainstream of development. Digital control system for nuclear power plant control "nerve center", its a part of any problems, are likely to lead to the part of control system failure or cause a system failure, eventually led to the reactor shutdown, turbine trip safety action, this will greatly affect the economic benefits of the power station; they may even lead to core damage, release of radioactive material into the environment medium ultimate accident, ultimately endanger public security. Therefore, the digital control system reliability evaluation is crucial. Due to the complexity of digital control system, it is great significance to put forward a set of effective methodology for evaluation of digital control system reliability.Along with the people study the PSA methods in-depth, a lot of domestic and foreign research institutions began to try different approaches to the nuclear plant digital control system reliability evaluation. Due to various research perspective, and need to resolve different issues, resulting in the current evaluation method, although targeted, but generally have limitations, it is difficult to quantify, and applying in engineer, so it is unable to form a complete set of both theoretical support, and can complete evaluation system for engineering application. Based on the above reasons, this paper on the basis of investigation, to do the following research:First of all, in this paper, a previous thought of system layering according to the physical equipments has been changed, system layering according to the function is used (reliability definition emphasizes the completion of a specified function). And the original system, unit, module, and element four layers structure, has been changed into the system, classical systems and basic unit consisting of three layers structure. In this way, it is more easy to do reliability evaluation for every layer, and finally get the whole system reliability evaluation results. A new methodology for digital control system reliability evaluation is provided. Then, this paper draws on the reliability of mechanical equipment evaluation model:strength-load model. And according to the digital equipment failure characteristics, namely multiple impact caused failure, rather than a single impact by multiple, a new kind of digital control system reliability evaluation model:generalized dimensionless strength-load model is put forward. And on the basis of the model, the dynamic model and considering the common cause failure model are also put forward. Considering the need of engineering application, the failure rate is known, the multi-fault impact model (MESH) is improved. Finally, based on functional hierarchical thought and generalized dimensionless strength-load model as the foundation, to the practical engineering application oriented, with engineering design documents:system network structure diagram as input, a set of graphical modeling method is established, namely the system network structure diagram analysis method. based on function layer. This paper also provide the self-defined symbol and basic concept for the method, while the design of the calculation procedure, and useing a real power plant as the research object.This paper puts forward new diea:based on functional hierarchical, and a complete set of effective digital control system reliability evaluation is presented. General dimensionless strength-load model is proposed to solve the problems of digital equipment which is easy to suffer from multiple types of loads, and common cause failure model under the condition of failure rate unknown. When the failure rate is unknown, the original fault impact model (MESH) is improved, betterly solves the problem. Finally, combined with the engineering practice, combining the model and system network structure diagram analysis method, the engineering actual digital control system reliability evaluation is resolved.