Control Strategy Research on HOTSG Hydrodynamic Instability During ELPO Mode for Two-Loop SMR

Helical coil once-through steam generator (HOTSG) has advantages of compact structure and high heat transfer efficiency, which is widely used in the design of advanced small reactor. Hydrodynamic instability is a problem that must be avoided in HOTSG design, especially in low power operation where the phenomenon may occur easily. In this paper, the flow instability control strategy of HOTSG under extended low power operation (ELPO) of two-loop small PWR is studied, and a grouping operation (HOTSG are fed by two feed-water pumps) control strategy is proposed. The structure of HOTSG is modeled by using the self-developed system analysis program LOCUST to analyze and compare the hydrodynamic instability under low power operation. The steady-state operation, up and down operation processes of HOTSG are analyzed, and the grouping operation and overall operation (HOTSG are fed by the same feed-water pump) conditions are considered. The analysis results show that the flow instability of HOTSG occurs in the 10% FP power platform when it is operated with overall strategy. Conversely, the flow instability can be avoided when it is operated with grouping strategy, and the up and down operation processes are also stable. Therefore, in view of the low power operation of HOTSG, the grouping operation control strategy can alleviate or even solve the flow instability problem as an effective way. The cooperative resistance design of throttle can improve the operation stability and economy of the plant, which is of great significance to ensure the stable operation of the unit.