Patent GB-1119858-A (GB)
Title: Reactor safety device
Inventor: OLSSON CURT SIGVARD
IPC: G21C7/12
Filed: 1965-10-13
Abstract: 1,119,858. Controlling reactors. ATOMENERGI A.B. 13 Oct., 1965 [15 Oct., 1964], No. 43463/65. Heading G6C. A device for operating a neutron-absorbing rod in a nuclear reactor comprises a slide 3 either supporting a neutron-absorbing rod or itself constituting the rod and axially movable in a cylinder 1 above the reactor core 37, the upper portion of the slide 3 being formed as a plunger 5, and means for supplying a pres. surized fluid to the space 23 defined by the cylinder 1, the slide 3 and the plunger 5 for holding the slide 3 in its upper position. The cylinder 1 and/or the slide 3 has at least one recessed portion along its entire operative length forming a channel through which the pressurized fluid leaves the space when the slide 3 leaves its upper position after the supply of pressurized fluid has been cut off, to the effect that the neutron-absorbing rod falls into the core 37 by its own weight and relatively freely. A water-cooled nuclear reactor containing such a device comprises a tank 35 housing the core 37 and a handling machine with a central stem 39 for removing used fuel from and inserting new fuel into the core 37. The lower portion of the cylinder 1 is situated below the water level 51 in the tank 35. An hydraulic pressure is maintained in the space 23 by a pump 47 in a conduit 25, 29 which has its lower end connected to the bottom of the tank 35 and contains a 3-way magnetic valve 27. The space 23 may be connected to the bottom of the tank 35 through a by-pass conduit 33, whereupon the pressure in the space 23 falls and the slide 3 begins to move downwards by its own weight. As soon as a seal ring 7 which is provided in an annular groove in the plunger 5 (as shown in Fig. 2) comes out of engagement with a raised seal surface 11 on the inner wall of the cylinder 1, the water in the space 23 flows upward through the annular space 6 between the plunger 5 and the cylinder 1 and the slide 3 can move much faster. Its downward movement is limited by the lower surface of the plunger 5 coming into contact with a flange 13 on the end of the cylinder 1. A spring (not shown) may be provided around the slide 3 to be compressed between the plunger 5 and the flange 13. Three axially extending grooves 15 are provided on the inner surface of the flange 13 and the pressurized water in the space 23, when the slide 3 is in its uppermost position, flows from the space 23 through the channels formed between a seal ring 17 in the slide 3 and the grooves 15. Along its entire operative length the inner wall of the cylinder 1 has an annular portion 21 recessed in relation to the seal surface 11. In another embodiment (Fig. 3, not shown), the cylinder 1 has no recessed portion but the slide 3 has on its outer wall an annular recessed portion (49), while in a further embodiment (Figs. 4 and 5, not shown), there are recessed portions consisting of longitudinal grooves (21a, 49a) on both the cylinder 1 and the slide 3. The central stem 39 of the handling machine can be turned in any direction and arms 55 carry a vertical member 53 which supports a telescopic lifting member 57. This can be raised and lowered by means of a wire 59 operated by a drum 60. The lifting member 57 carries a grip member 61 which can be lowered through the cylinder 1 to lift the slide 3 back from the bottom of the cylinder 1 to its uppermost position. The top of the slide 3 has an internal flange 10 by means of which the slide can be seized by the grip member 61 to be lifted by the lifting member 57.