Patent GB-1488075-A (GB)
Title: Arrangement for protecting the containment vessel dome of a nuclear reactor
IPC: G21C19/02
Filed: 1975-04-07
Abstract: 1488075 Nuclear reactors; refuelling nuclear reactors COMMISSARIAT A L'ENERGIE ATOMIQUE 7 April 1975 [11 April 1974 10 June 1974] 14173/75 Heading G6C A nuclear reactor, especially a fast sodium cooled reactor, comprising a top shield slab 3 mounting an equipment units, for example a refuelling device 15, includes an arrangement whereby, in the event of tilting of the shield slab, the equipment unit separates into two portions thereby eliminating the possibility of damage to a surrounding containment structure 60. The refuelling device 15 includes a rotatable member 24 having guide rails forming extensions of inclined ramps, one of which 13 passes to adjacent the reactor core 4 and the other of which 17 passes to adjacent a fuel store. For refuelling purposes, a transfer flask 11 is movable on a carriage 12 which rides on one or other of the ramps 13, 17. In order to effect transfer of the carriage 12 from one ramp to the other, it is hauled from the one ramp on to the rotatable member 24. The latter is then rotated through an appropriate angle, for example 180 degrees, and the carriage then lowered down the other ramp. The axis 23 of rotation of the rotatable member 24 is vertical. The refuelling device 15 includes an inner, leak-tight casing 35 and an outer shielding structure 33. In one embodiment (Fig. 2) the arrangement for procuring separation of the refuelling device 15, in the event of tilting of the shield slab 3 to a displaced position 3<SP>1</SP>, comprises provision for shearing, as at 74, of the inner, leak-tight casing 35 and the outer shielding structure 33; the refuelling device 15 thus separates into an upper section and lower section, these being coupled by rigid components, in this embodiment comprising a pair of arms, such as arm 62, pivoted to both sections such as to allow tilting of the lower section and cause vertical rectilinear movement of the other section. Such movement of the upper section is guided by co-operation between a guide shoe 70 on the upper section and a complementary guide 72 on the containment structure 60. A drive shaft 28 of the rotatable member comprises a coupling 80 having spigot and socket parts which separate freely upon relative lateral movement between the upper and lower sections of the refuelling device 15. In a second embodiment (Fig. 3) the rigid components affording guidance between the upper and lower sections of the refuelling device 15 comprise, instead of the pivoted arms of the previous embodiment, guide rollers 82. A detailed description of the refuelling device 15 is given with reference to Fig. 4. An unusual feature of this device comprises the provision on each ramp 113, 117 of a respective carriage 112; the rotatable member 124 includes two sets of guide rails, whereby during a refuelling operation both carriages may be moved simultaneously up their associated ramp and on to the rotatable member, for transfer on to the opposite ramps and subsequent lowering thereon. Although the detailed description is given with reference to a pair of ramps 113, 117, it is stated that a larger number of ramps may be provided, whereby transfer operations may be performed between any one of a number of fuel stores outside the reactor containment vessel and the reactor core. In such an arrangement the rotatable member 124 of the refuelling device 115 is rotatable through appropriate angles less than 180 degrees.