Hydraulic characteristics investigation on a novel multi-plate throttle entry tube of fast reactor control rod subassembly

Abstract

As the only reactivity control method, the Control Rod Subassembly (CRSA) is employed to control the startup, shutdown and power regulation of Sodium-cooled Fast Reactor (SFR). The entry tube is an essential structure component of CRSA, serving not only as the inlet of liquid sodium but also as the support and guidance for CRSA. To address the shortcomings of traditional straight-through entry tube in terms of throttling effect and experiment cost, a novel Multi-plate Throttle Entry Tube (MTET) is designed and manufactured in this investigation. MTET hydraulic characteristics and geometrical parameter effect are investigated detailed by hydraulic experiments and numerical simulations. Based on the similarity analysis, the alternative hydraulic experiments are conducted on MTETs with different geometrical parameters. Experiment results reveal that MTET can achieve 299.12 kPa at the rated mass flow rate of 1.20 kg/s, with a relative error of −0.29%, which also verifies the rationality of this new MTET. In view of the design requirements of SFR, the optimal geometrical parameters are determined as three throttling holes of 10 mm in diameter and five throttling plates of 41 mm in width. Additionally, numerical results provide an evident that the geometrical parameters are pivotal influence factors to the MTET hydraulic characteristics, such as throttling plate width, throttling hole arrangement, connecting rod length, and throttling plate pitch. Increasing the throttling plate width and extending the throttling plate pitch can both improve the throttling effect of MTET. By comparison, the throttling effect of MTET is more sensitive to the throttling hole arrangement rather than the connecting rod length. It's important to note that the modification of connecting rod length needs to be carefully evaluated. Meanwhile, the non-uniform arrangement in multi-plate throttle is another solution to adjust the MTET hydraulic characteristics, which only needs to modify the width of single throttling plate. Compared to the fifth throttling plate (along the coolant flow direction), the adjustment efficiency of the first throttling plate increases by more than 4%. Therefore, the significant pressure drop should be adjusted by modifying the widths of upstream throttling plates, while the modification of downstream throttling plates is more suitable for the minor pressure drop adjustment. This innovative design demonstrates the improved throttling effect of MTET, as the promising structure optimization for CRSA and other subassembly of SFR.