Patent GB-1150157-A (GB)
Title: Improvements in Velocity Control Mechanisms.
IPC: G21C7/16
Filed: 1966-09-12
Abstract: 1,150,157. Hydrodynamic brakes. GENERAL ELECTRIC CO. 12 Sept., 1966 [15 Sept., 1965], No. 40558/66. Heading F2E. [Also in Division G6]  In a mechanism for controlling the relative velocity between a hollow body 44 and a control body 41, 50, the hollow body 44 is filled with liquid and relative reciprocation of the bodies causes fluid to flow in a space between the two bodies such that one of the bodies is provided with a cavity which opens into the space between the bodies and is shaped to divert more fluid into the cavity for generating more turbulence in fluid flow through the space in one direction than in the other direction of relative movement. As shown in Figs. 1 and 5 the mechanism is applied to a water-cooled nuclear reactor 10 having cruciform control elements 41 each adapted to be urged upwardly by actuation of a fluidcontrolled piston 42 into the reactor core 18. Each of the control elements 41 passes through a guide tube 44 filled with coolant. Downwardly-shaped teeth are formed on toothed blades 52 on the lower portion of the control elements 41 such that when the piston is pressurized through the line 43 to move the control rod upwardly, water is displaced in the guide tube to flow downwardly through the space 61 and towards the lower end of the control body. When the pressure in the line 43 is reduced, the control rod and body move downwardly so that water is forced to flow upwardly through the space 61. The shape of the ridges and teeth on the control body provides a high hydrodynamic resistance force to upward flow of liquid through the space between the teeth and the guide tube and yet offers a much lower resistance to the flow of water in the opposite direction so that it is possible to move the control rods into the nuclear reactor rapidly should an emergency arise requiring quick shut-down of the unit. Conversely, if some mechanical failure should cause loss of pressure in one of the supply lines 43 or if there should be mechanical failure or rupture of the coupling which would let the respective control rod be free to move downwardly, the hydrodynamic drag of the downwardly facing teeth of the control body limits the rate at which the control rod can move down. In an alternative embodiment shown in Fig. 7 a conical-shaped member 80 is disposed in a vertical cylindrical guide tube 80. The upper end of a drive piston 88 is secured to a hub member 84 screwed to the cone-shaped member 80. As the piston is moved up and down as previously described to move a control rod 105 upwardly liquid is forced downwardly past the convex part 102 of the cone and through a space 98. A rigid skirt 94 is secured to and spaced below the cone by four vertical webs 96 and wheels 97 are provided at the periphery of the skirt mounted to roll against the interior of the guide tube 82 and keep the cone and skirt spaced from the guide tube to form a uniform annular flow space 98 between the cone skirt and the guide tube. The shape of the upper periphery of the cone is such that the liquid is subject to a relatively low resistance in flowing through the space so that the control rod can be moved upwardly fairly quickly. Conversely, because of mechanical failure, if the control rod starts to move downward rapidly some liquid is forced upwardly through the hub through a channel 100 into the bottom of the cone. The liquid is then diverted downwardly and outwardly through the annular slot 99 formed between the skirt and the cone to create turbulence of fluid flow to increase the resistance to the movement downwardly of the control rods. In a further embodiment (Fig. 8, not shown), a conical deflector is attached to the guide tube instead of being attached to the cylindrical control rod.