872,092. Controlling reactors. NUCLEAR POWER PLANT CO. Ltd. Aug. 14, 1959 [Sept. 8, 1958], No. 28768/58. Class 39(4). A safety release mechanism for releasing a member from a parent member in response to changes in pressure in a fluid in which the releasable member is immersed comprises a push rod attached to the releasable member and operable to trip a latch mechanism joining the releasable member to the parent member and a pressure sensitive device located in the releasable member and forming an enclosed space therein; the pressure sensitive device being responsive to pressure changes between the enclosed space and fluid surrounding the releasable member and exerting a force on the push rod sufficient to trip the latch mechanism when a predetermined pressure change occurs. Fig. 1 shows an arrangement for releasing a control or safety rod in a gascooled nuclear reactor. The control rod comprises a tube 2 containing boron and arranged between inner and outer stainless steel tubes 1, 3. The outer tube 1 is welded to a tube 21 attached to a lifting head 13. A bellows 6 provided with an orifice 9 forms an enclosed chamber within the control rod so that if the gas pressure outside the rod falls, the bellows expand pushing up push rods 10 which act on a plate 15 and a further push rod 14 to actuate a latch mechanism and release the control rod. If the temperature of the gas around the control rod rises excessively tube 21 expands thus causing an end cap 11 to press down on the ends of levers 26 which push up the rods 10 and release the control rod. To retrieve the rod from the reactor the member 20 is lowered by a rope or chain until it contacts the top of the rod where, due to the geometry of the system, the pawls 24 under the weight of member 20 are rotated into the locking position by cam action of the pawls 24 on the inclined faces of lifting head 13.
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