Structure And Reliability Research Of Digital Reactor Protection System In Nuclear Power Plant

Nuclear power is an important kind of energy sources for modern society, but the controlled nuclear power in Nuclear Power Plant (NPP) can only be released in reactors. Reactor Protection System (RPS) in NPP monitors the status of the reactor, and takes some certain safety actions when it gets the conclusion that the reactor is under the unacceptable conditions. RPS in NPP is one of systems which need the highest safety level, because RPS in NPP is the last protection barrier for the reactor. With this requirement, reliability is the most significant characteristic which should be concerned.Comparing with traditional RPS in NPP employed total analog technology, which has been long behind the time. Digital RPS has many distinct advantages, and it is the certain direction of development of RPS in NPP.In this dissertation it reviews RPS development in the past decades, introduces the current situation and analyses the technical characteristic of digital RPS in NPP in the world. On the base of the analysis, a new design of digital RPS for NPP with single level in the train and redundant linear topology network is accomplished. According to kinds of test and calculation, it proves that the new system in the design has advantage of system character.The primary originalities in this dissertation are as follows:Firstly, a new RPS with single level in the train is designed. Comparing with TXS system in AREVA Co. based on the same hardware, in the new system of the design it changes three levels into single level in the train. So it simplifies the structure of system trains and reduces the number of modules.Secondly, in the new system of the design it is divided into two sub-systems: Reactor Tip System (RTS) and Engineering Safety Features Actuation System (ESFAS), these systems run in two processor modules separately. So it improves the ability of calculation and reduces the load of CPU.Thirdly, in order to reducing the rate of mis-action, processor modules in the new system of the design are configured with "Master-Checker" structure.Fourthly, the communication among four trains in new system of design is realized by the redundant linear topology network, it could improve the reliability of the system.At last, the logic of Breaker sub-system is added into the digital Reactor Protection system, it improves the reflection time of actuation signal.In this dissertation, it demonstrates that the new system of the design is better than TXS system at system reaction time by the calculation and analysis of the system reaction time in the worst case. At the same time, a test on the processor module load is carried out. The result shows that the new system of design is available in CPU load.A method is used to estimate reliability of the new digital RPS. Comparing the result of estimation for the new system of the design and TXS system, it shows that RTS in the new system of design has obvious advantage of reliability, and ESFAS in the new system of the design, because of priority module, has little advantage of reliability. But in general, the new system of the design has advantage of system character.Finally, based on national standards and norms, Failure Mode and Effect Analysis(FMEA) is carried out for the new system of the design, and "RISK SPECTRUM" analysis software is used to calculate the mean unavailability of the new system of the design. The theories used in "RISK SPECTRUM" are Minimal Cut Set analysis and Failure Tree models. Comparing with TXS system, the result of calculation in detail shows again that the new system of the design has advantage of reliability.The results of this research provide reference for domestic study in digital RPS in NPP. And it is good experience in designing digital RPS in NPP.