Reliability Optimization of the Filling and Discharging System for Lead-Based Fast Reactor

The lead-based fast reactor is one of the most promising advanced Gen-IV (generation IV) type nuclear power reactors. The filling and discharging system in the primary circuit of the lead-based fast reactor, which is an important system for ensuring the safety of reactor operation, is designed to adjust the coolant level in the reactor vessel. The system is filled with liquid metal, which contains radioactive materials, and it requires high level of safety and reliability. This study performed preliminary reliability analysis for the filling and discharging system of the lead-based fast reactor by using Fault Tree Analysis method. Minimal Cut Sets and failure probability of the filling and discharging system were obtained by using Reliability and Probabilistic Safety Assessment program RiskA, which was developed by Institute of Nuclear Energy Safety Technology, HFIPS, Chinese Academy of Sciences. Some other quantitative analysis results were also obtained, including importance and sensitivity analysis. The reliability analysis results indicated two flaws of the original system design, one is the low reliability, and the other is the lack of redundancy. According to calculation results of original system, an optimized conceptual design was proposed by the designers. The reliability analysis of the optimized system was performed. And the results indicated that the failure probability of the optimized design is reduced by two orders of magnitude and the optimized design is more reliable than the original design. This risk-informed approach can find the weakness in the conceptual design and guide the further design.