Patent Number: 046719210
Section: description

Referring now to the drawings, the references used in FIGS. 1 to 9 (from 1 to 21) all have the same meaning. These Figures illustrate the invention with the aid of a particular embodiment intended for compacting 264 pencils of a conventional fuel element for nuclear reactor. In this fuel element, the pencils are distributed in a lattice of 17 lines and 17 columns, with square mesh of side (or pitch) equal to p =12.6 mm. In addition to the 264 pencils, the lattice comprises 25 tubes without fuel forming the skeleton of the fuel element (17.times.17=264+25). As shown in FIG. 1, the compacting device 1 according to the invention comprises a plurality of tubes (for example 66) spaced apart from one another at their upper ends and in contact with one another at their lower ends. The upper ends 2a of the tubes are rendered fast with the lower face of a thick plate or flange 3 whose surface is substantialy equal to the section of a fuel element, in which through holes 4, widening outwardly, i.e. on the side opposite the tubes 2 (cf. FIGS. 2 and 3), are pierced. There are as many holes 4 as tubes 2 and each of them is disposed in line with the corresponding hole, so that said hole extends the interior of the tube. In the flange 3, the 66 holes 4 are centred at points corresponding to positions of pencils in the lattice of 264 pencils of the fuel element, but the distance separating the centres of two adjacent holes 4 is at least equal to P =2p. In this way, there is more space available for gripping said pencils. Moreover, the relative arrangement of the 66 holes 4 in the flange 3 is such that, if the flange 3 is rotated through four successive quarter turns around its centre 5, the 66 holes 4 would occupy the 264 locations of the pencils of the fuel element. In this way, by taking from the fuel element the pencils according to the distribution of the holes 4 of the flange 3 and by rotating said fuel element about its longitudinal axis between each taking, all the 264 pencils are taken in four takings, and, at each taking, the pencils taken out of the fuel element may be introduced into holes 4 without difficulty, since they present the same relative arrangement. The lower ends 2b of the tubes 2 are rendered fast with the upper face of a plate or flange 6, in which holes 7 are pierced. There are as many holes 7 as tubes 2 and each of them is extended by one of said holes. As shown in FIG. 4, each hole 7 (except on the edges) is surrounded by six holes 7 which are adjacent thereto. The tubes 2 thus pass from a spaced apart disposition with square mesh (at flange 3 level) to a close disposition with hexagonal mesh (at flange 6 level). Moreover, rigid wires 8 are fixed to the lower face of the flange 6, in the interstices between the ends 2b of the tubes 2, to extend said tubes as immaterially as possible by converging them towards one another until the outer contour of each of the fuel pencils is defined. At their ends opposite the flange 6, the wires 8 are protected by a plate 9 (cf. FIG. 5) inside which is made a cut-out 9a corresponding to the section of a compact bundle of 66 pencils. The ends of the peripheral wires 8 are rendered fast with the plate 9, the others being located inside the cut-out 9a. In this way, it will be readily understood that 66 pencils introduced simultaneously in the holes 4 of the flange 3 are guided by the tubes 2, the holes 7 then the wires 8 and the plate 9 to form a bundle which presents at the most compact location a section such that it can be introduced into a container of minimum section. Of course, the degree of compacting obtained downstream of flange 6 depends on the outer diameter, therefore on the wall thickness, of the tubes 2 at their lower end 2b. The rigid wires complete compacting. The gradient of compacting, and therefore the length of the tubes 2, depend on the flexibility of the pencils and on the clearance between the inner diameter of the tubes 2 and the pencils. Experience has shown that, for conventional pencils of 4 m in length and 9.5 mm in diameter, tubes with a length of 2.5 to 3 m and 10.5 mm in inner diameter extended by wires of about 0.5 mm in length gave good results. FIGS. 6 to 9 schematically illustrate an application of the process according to the invention. FIGS. 8 and 9 show a view at 90.degree. with respect to that of FIGS. 6 and 7. On the bottom 10 of a cooling and deactivation pond are disposed horizontal support plates 11 and adapted to rotate about their vertical axis, and handling mechanisms 13 and 14. Plumb with the compacting device 1 is mounted an intermediate reception device 15 inside which the device 1, displaced by the mechanism 14 (shown in FIGS. 8 and 9) may penetrate. This intermediate reception device 15 comprises a plurality of plates parallel to one another and identical to plate of the device 1. The different plates 16 may move vertically, whilst remaining horizontal, along vertical rails 17. In the position shown in FIGS. 6 and 7, the compacting device 1 is located between the rails and the plates 16 are in their low position. Furthermore, a fuel element 18 is vertically centred on the rotating plate 12. The mechanism 13 (shown in FIGS. 6 and 7) enables a device 19 for extracting the pencils 20 from the fuel element 18, to be manoeuvred. The device 19 is guided by mechanism 13 above the element 18 and takes therefrom 66 pencils distributed as shown in FIG. 2 (cf. FIG. 6). The mechanism 13 then displaces the device 19 to guide it plumb with device 1. The 66 pencils descend vertically and, after having passed through device 1 by the action of gravity, they are compacted and released. The bundle of pencils 20 on leaving the device 1 passes through the different assembled plates 16 (cf. FIG. 7). The mechanism 14 is then actuated to raise the device 1 in order to remove it from the rails 17, whilst the plates 16 are also manoeuvred so that, sliding upwardly, they move away from one another. In this way, the device 1 releases the pencils 20 which are, however, maintained compacted by the spaced apart plates 16 (cf. FIG. 8). Finally, the mechanism 14 brings plumb with the bundle of pencils contained in the intermediate reception device 15, a container 21 which is lowered so that the compacted pencils 20 pass in said container 21 (cf. FIG. 9). After these operations, a quarter of the pencils contained in the fuel element 18 has therefore been placed in a container. By recommencing the operation four times after rotation of plates 11 and 12 (plate 11 bearing three other containers 21--not shown in the Figures), all the pencils of element 18 are placed in a container.