Experimental Study on Hot State Performance of Control Rod Hydraulic Drive System

The control rod hydraulic drive system (CRHDS) represents an innovative built-in control rod drive technology and serves as a critical actuator for reactivity control and power regulation in integrated nuclear reactors. The system employs a circulation pump to force pressurized water through an integrated valve. This valve regulates the extension and retraction of three coaxially nested hydraulic cylinders, enabling the engagement and disengagement of a pawl with the control rod drive shaft. Consequently, the system achieves control rod step-up, step-down, and rapid retraction. While existing research has largely focused on individual components under ambient temperature conditions, there is a paucity of studies regarding the overall performance of the drive system in high-temperature environments. Consequently, this paper experimentally investigates the thermal performance of the CRHDS from a system-level perspective, aiming to characterize the variation in key operating parameters relative to changing operating conditions. In this paper, the composition and operating principles of the CRHDS were analyzed, and the construction of a full-scale hot state performance test rig was described. Experiments were conducted in which control rods were positioned at typical step heights of 1, 30, and 54. The loop temperature was incrementally adjusted to 50, 100, 150, 200, and 230 °C. At each temperature setpoint, system pressurization and depressurization tests were performed under drive pressures of 650, 800, 850, and 1 000 kPa, followed by rod drop tests. To facilitate real-time monitoring of internal and external pressures, differential pressure transducers were installed at the inlets of the three hydraulic cylinders. Furthermore, rod position sensors were integrated into the test assembly to track control rod movement during step-up, step-down, and rapid retraction operations. The resulting data were analyzed to characterize the variations in key characteristic parameters as functions of pressure, temperature, and rod position. The results indicate that the drive system exhibits distinct characteristic inflection and equilibrium points during both pressurization and depressurization processes. These points correspond to the moment when the hydraulic cylinder reaches its final position and the time when the internal pressure stabilizes, respectively. Increasing drive pressure accelerates the pressurization process, reducing the time required but elevating the pressure level; Conversely, the depressurization process slows due to increased resistance, resulting in extended durations and higher pressures. Increasing loop temperature accelerates both processes, shortening the time for actuated components to reach their final positions, while simultaneously prolonging pressurization stabilization time and reducing depressurization stabilization time. As the control rod position rises, pressurization resistance increases and depressurization resistance decreases, leading to delayed pressurization and shorter depressurization time. Additionally, for rod insertion, the insertion time decreases as temperature rises. These findings provide an experimental basis for the design optimization and parameter selection of the CRHDS.