Patent GB-1143752-A (GB)
IPC: G21C7/20
Abstract: 1,143,752. Controlling reactors. BABCOCK & WILCOX CO. 19 Aug., 1966 [19 Aug., 1965], No. 37198/66. Heading G6C. Control rod actuating means comprise means for applying to one end of a control rod, of which the other end is subject to fluid coolant pressure and which is movable in a guide tube in the reactor core, a fluid pressure higher than the coolant pressure for driving the control rod to a position removed from the core or a fluid pressure lower than the coolant pressure for driving the control rod to a position inserted in the core, and latching means for retaining the control rod in the inserted position which are adapted to permit movement of the control rod towards the removed position by the application to the first mentioned end of the control rod, for an appropriate period of time, of a fluid pressure lower than the the coolant pressure and then of one higher than coolant pressure. In one embodiment, a hold-down catch member 46 is threadedly secured to the lower end of a latch housing 12 within which it extends upwardly. This catch member is longitudinally slotted along most of its length from the upper end to form a plurality of spaced resilient fingers 50. The catch releasing device comprises a snubber piston 58 having a fluid-tight fit within a housing 30 and provided with a smaller diameter sleeve portion 60 extending downwardly through a bore 62 in the lower end portion 29 of the housing 30, terminating in a downwardly and inwardly bevelled surface 66. The surface 66 normally engages upwardly and outwardly bevelled surfaces 52 at the uppermost ends of the fingers 50 when the snubber piston 58 is at its uppermost position (Fig. 1A). The lower portion 84 of the control rod terminates in a frusto-conical surface 90 which connects to a smaller diameter end assembly 91.. An end cap 92 having a frusto-conical lower end surface 93 is secured to the lower end of a downwardly tapering portion 94 of the assembly 91. An annular shoulder 95 between the end cap 92 and the tapering portion 94 is engaged by catching surfaces 56 on the finger members 50 when the control rod is in the inserted position (Fig. 1A). The actuating means are secured to the lower grid plate 44 of a cluster-type fuel element. When the fuel element is positioned within the reactor core, the end portion 16 of the latch housing 12 is located in a cup-shaped member 96 permanently disposed within the reactor and connected to an actuator fluid line 97 which extends through the pressure vessel wall to an external source of actuator fluid. In order to effect raising of the control rod from its lower latched position, a lower pressure than that of the reactor coolant is applied through the line 97, resulting in the snubber piston moving downwardly against the action of a spring 24. As the piston 58 and the sleeve portion 60 move downwardly, the bevelled surface 66 at the lower end of the sleeve portion 60 initially in engagement with the inwardly sloping surfaces 52 of the upper ends of the fingers 50 displaces them radially outwardly to a position (Fig. 1B) in which the catching surfaces 56 no longer engage the annular shoulder 95 of the control rod. High pressure fluid is then admitted to the line 97 and the control rod driven upwardly, the fingers 50 returning to a catching position after the annular shoulder 95 has passed the catching surfaces 56. The pressure differential between the line 97 and the top of the control rod guide tube 72 is sufficient to drive the control rod upwardly out of the reactor core. In downward travel of the control rod, as the control rod reaches the lower end of the guide tube 72, its lower end enters a labyrinth sleeve 76 and there is then less flow path area available for the escape of fluid from the space below an enlarged collar section 86 of the control rod, the speed of the control rod thus being reduced. The frusto-conical surface 90 of the control rod then mates with a resiliently mounted seating surface 70 in the upper end of the snubber piston 58 which absorbs the initial impact of the control rod. Two-position control rods of the above type may be provided in a reactor for safety purposes. In addition, a multiplicity of such control rods may be provided, each being capable of effecting only a small reactivity charge and the reactor being controlled by varying the number of rods in the removed position while the remaining rods are in the inserted position. The actuating fluid may be the same as that used as coolant, while the reactor may be a pressurized water or a steam cooled reactor.