Development of hydraulically driven control rod drive mechanism for passive in-core cooling system (pincs)

Abstract

A passive in-core cooling system (PINCs) was introduced by Ulsan National Institute of Science and Technology (UNIST) to enhance the safety of pressurized water reactors and small modular reactors. This system consists of a hydraulic control rod drive mechanism (CRDM), a hybrid control rod that combines the heat pipe with the control rod, and heat sinks. In the study, the main objective is to analyze the mechanism of a new type of the hydraulic CRDM to achieve the unique features of PINCs. Hydraulic CRDM is a fully passive system that can be safe shutdown without additional electric power and signal. The experimental study focuses on the force balance in the system to control the vertical motion of the hybrid control rods. To analyze the dynamic behavior of hydraulic CRDM equipped with the hybrid control rods, the simple transient model was developed. The positions of the hybrid control rod were stably controlled according to inlet flow, and the results are calculated by the developed simple transient model. It is possible to determine the control rod location from the change of the inlet flow rates at each step. Drop test results yield good agreement with those predicted by the theoretical model, resulting in percentage errors within ±15 %. The experimental tests were then conducted for both the step control and the drop test. These showed the possibility of successfully applying the in-core hydraulic drive system to PINCs.