942,157. Nuclear reactors. UNITED KING- DOM ATOMIC ENERGY AUTHORITY. April 2, 1962 [April 25, 1961], No. 14992/61. Heading G6C. An energy dissipation device for use in a nuclear reactor to dissipate energy from a falling body such as a control rod or a fuel element is held against displacement by coolant flow by means of a latch having two parts one engageable with the other, one part attached to the device and the other to the reactor structure, the parts being readily engageable by elastic deformation of the part attached to the device but disengageable only by stressing the latch until the part attached to the device deforms plastically. As shown in Fig. 1, a reactor moderator structure comprises columns of graphite blocks 36 each supported by a single block 37 supported in turn by a steel plate 40. A collapsible tube 13 of stainless steel is secured at its lower end to a sleeve 3 and at its upper end to a tubular support member 17 which has welded to it an inner former tube 20 and an outer shroud tube 21. The member 17 has an integral support sleeve 25 to which is keyed a graphite sleeve 27 carrying at its upper end a steel impact ring 28. A fuel element cluster having an outer graphite sleeve 33 rests on the ring 28. Five equi-spaced spring claws 9 of stainless steel are secured to the sleeve 3 and have upwardly and outwardly turned ends 11 which pass through slots 12 in the sleeve 3. The device is installed in the reactor under "off-load" conditions by assembling together the member 17,the tubes 13, 20 and 21, and the sleeve 3 and lowering the assembly into a tube 5 forming part of the reactor structure. When the spring claws 9 meet the conical upper face 7 of a ring 4 secured to the tube 5 they are deflected inwardly under elastic deformation to allow the further lowering of the assembly until the position shown in Fig. 1B is reached. To remove the fuel element cluster, a grab is lowered into the channel 34 to engage the cluster which is then withdrawn upwardly. Should the cluster inadvertently drop during its removal it falls and strikes the impact ring 28, the force.of impact being absorbed by the progressive collapsing of the tube 13 which corrugates along its length in the manner indicated by the preformed corrugated portion 16. The former tube 20 assists in centralising the collapsed tube 13 and the shroud tube 21 controls its outer diameter so that it does not jam in the tube 5. In order to remove the device, e.g. so as to replace a tube 13 deformed by a fallen fuel cluster, a tool is lowered into the moderator structure having remotely operated radially expansible members which engage the conical face 23 of the member 17 and a large upward force is then applied to the tool which stresses the ends 11 of the claws 9 until they deform plastically and move inwardly over the lower face 8 of the ring 4 and through the slots 12. One type of such tool is described in detail. Specifications 783, 094 and 873,073 are referred to.
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