The paper designed a small rapid power reduction system (SRPRS) based on gray control rods for pressurized nuclear power plants, and technical scheme of SRPRS was proposed in the paper. Different to current RPRS for turbine trip, SRPRS was designed for feed water pump trip. When one FWP happened, partial of gray banks dropped into the reactor core to reduce the core power, and reactor trip due to power mismatch between primary and secondary sides would be avoided. The paper researched the basic principles of SRPRS, and demonstrated the feasibility of using SRPRS in pressurized nuclear power plants with gray control rods. The small rapid power reduction system designed in the paper includes three stages: activation, recovery and normal operation. Each stage can automatically complete control actions with a few human intervention. The small rapid power reduction system makes full use of the gray control rod characteristics: low reactivity worth and small disturbance to core power distribution, so it can achieve rapid reduction of core power while maintaining a flat power distribution. Meanwhile, since the control rod insertion limit set in the technical specification does not limit the insertion of gray control rods, the operation of small rapid power reduction system will not exceed the requirements of the technical specification for normal operation. The paper designed a “slope factor” in small rapid power reduction system. By calculating the slope factor in advance and judging the rods to be dropped in real time, the small rapid power reduction system can perform its function at any initial gray control rod position.

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