Modeling and safety analysis of supercritical CO2 Brayton cycle reactor system under loss of coolant accident (LOCA)

The supercritical CO2 (SCO2) Brayton cycle has the advantages of high efficiency, flexibility, and safety. It is highly compatible with Generation-IV reactors, making it one of the most promising energy conversion systems. However, the special physical properties of the working medium will lead to complex blowdown behavior when loss of coolant accident (LOCA) occurs, and the system performance needs to be clarified. In this work, the SCO2 blowdown model is developed. Combined with the system analysis program, the system transient behavior during the LOCA process is simulated, and the threat to the main equipment is evaluated. The results show that the accident process is closely related to the SCO2 state at different break locations. When LOCA occurs at the reactor inlet and outlet, the break discharge rate is small, but the reactor fuel temperature will increase significantly at the accident late stage. The compressor outlet LOCA has the largest discharge rate and the shortest coolant phase transition time (720 s, break diameter is 4 mm). In addition, the pre-pressurized containment can effectively reduce the amount of coolant leakage and maintain SCO2 in the supercritical state. However, for the compressor inlet LOCA, if the break area is further increased, even with the protection of the containment and inventory control system, the supercritical failure of SCO2 is inevitable. This study can provide a reference for the parameter response and accident process of the SCO2 Brayton cycle reactor system during LOCA.