The Study On The Method Of Safety Classification In Accelerator Driven Subcritical Reactor

Accelerator Driven subcritical System(ADS) is a new nuclear energy system for nuclear waste transmutation, new nuclear fuel and energy production. ADS system consists of accelerator, spallation target and subcritical reactor, and it uses proton which is speeded up by accelerator to bombard heavy metal spallation target and produce spallation neutron to drive nuclear reaction. ADS system can realize transmutating nuclear waste, reproducing nuclear fuel, producing energy. The lead-alloy has good neutronics, thermal hydraulics, and security features, and the lead based reactor was chosen as the main development direction of Chinese ADS reactors. The conceptual design of the lead-based reactor was completed by Institute of Nuclear Energy Safety Technology, Chinese Academy of Sciences. The Structure, System, Component(SSC) safety classification of nuclear power plant is the basis of the management requirements and regulations for nuclear power plant. The nuclear safety regulations stated that classifying the safety functions and the safety level correctly are the basis of selecting and adopting appropriate anti-seismic level, design specification and quality assurance. So it is a need to define the safety functions and perform safety classification in conceptual design stage. This is significant to improve the level of anti-seismic level, design specification and quality assurance for the lead-based reactor. The international norms and guidelines for Accelerator Driven Subcritical system have not been announced. So this study for the safety classification of SSC in the lead-based reactor is significant.At first, The internal and external SSC deterministic safety classification method and risk-informed safety classification method for PWR and BWR were investigated and studied; Secondly, the Master Logic Diagram(MLC) was used to deduce the safety functions for the the lead-based reactor, and then the safety functions were classified, and safety grade of SSC was determined according to safety function applicable to SSC, and this is the process of the deterministic safety classification method; Thirdly, the risk-informed safety classification method for the lead-based reactor were proposed according to the characteristic of the lead-based reactor; Lastly the two methods were used to perform case analysis for coolant system and lead-bismuth process system in the lead-based reactor. It is more rational and economical to adopt risk-informed safety classification than deterministic safety classification for the lead based reactor, but the risk-informed safety classification is not applicable for all systems. So it is necessary to combine the deterministic safety classification method and risk-informed safety classification method in the actual classification process.Future research efforts should aim at deterministic safety classification and risk-informed safety classification for SSC of other system in the lead-based reactor, and further improve two kinds of safety classification through the analysis of classification results.