Patent Number: 044629559
Section: description

DETAILED DESCRIPTION FIG. 1 shows a portion of a rack for a fuel element 1 fast at its lower part to a support structure 2 comprising part 3 for the engagement of the support structure 2 on the upper end of the support device according to the invention. The upper part of this support device is constituted by a support part 4 the upper portion of which, engaged in the part 3 of the support structure of the rack of fuel elements, is constructed in the shape of a vertical pin 6 including a shoulder 7 on which the structure 2 comes to rest with the interposition of support pads 8. Referring to FIGS. 1 and 2, it is seen that the lower portion of the part 4, of greater width than the upper portion, has a profiled portion 9 constituting a roller path. This roller path 9 is machined on the lower surface of the part 4. The support device comprises also a second intermediate support part 10 and a third support 11 itself resting on the bottom 12 of the pool of the fuel of the reactor. Between the support parts 4 and 10, are arranged two rollers with horizontal axes 14, 15, while between the support parts 10 and 11 are also arranged two rollers, with horizontal axes 17 and 18. The axes of the rollers 14 and 15 parallel with one another are oriented in a horizontal direction X, while the axes of the parallel rollers 17 and 18 are oriented in a second horizontal direction Y perpendicular to the direction X. The support part 10 has on its upper surface a roller track 20 and on its lower surface another roller track 21. The support part 11 comprises a roller track 24 on its upper surface. The rollers 14 and 15 are in contact through tracks 9 and 20 with the support parts 4 and 10, respectively. The rollers 17 and 18 are in contact with the parts 10 and 11 through tracks 21 and 24, respectively. The tracks 9 and 20 on the one hand, and 21 and 24 on the other hand, have a profiled shape in the transverse direction with respect to the rollers and have, in this direction, a succession of ramps (such as 9a, 9b and 9o on the roller path 9) having successively rising and descending profiles. The profiles of the ramp portions of two opposite, facing roller tracks (such as 9 and 20) are reversed. The rollers 14, 15, 17 and 18 comprise a cylindrical central portion and two terminal portions of short conical length enabling the centering of these rollers with respect to the roller tracks which are also profiled in the longitudinal direction with respect to the rollers to represent two inclined lateral parts such as 9e and 9f for the roller track 9. For example, the roller 15 comprises a cylindrical central portion 15a and two conical end parts 15b and 15c which come respectively into support on the inclined surfaces 9e and 9f of the roller track 9. The rollers have rotational axes (such as 25 for the roller 14) which enable the rollers 14 and 15 on the one hand and 17 and 18 on the other hand to be connected, through a linking element such as 27 traversed by the end of the axle 26 of the roller 15 on which is screwed a nut 28 (or the set 26', 27', 28' at the other end of the roller). The rollers 14 and 15 on the one hand and 17 and 18 on the other hand are thus connected to one another with a constant axial separation at each of their ends. Upon positioning of the support device on the bottom of the pool, the support parts and the rollers are kept in contact by means of screws 30 with a hexagonal head 31 enabling the supports 4 and 11 to be connected, and to exert a sufficient force between the supports and the rollers. When the support device has been placed in position, the linkages between the supports 4 and 11 are eliminated by removing the screws 30. The three support parts are then totally independent. When the borne element constituted by the fuel element rack is urged by a force in the direction X or in the direction Y, there occurs a movement of the element with respect to the support surface 12, either by movement of the set constituted by the borne element, the supports 4 and 10 as well as the set of upper rollers 14 and 15 with respect to the support part 11, by rolling of the roller 17 and 18 on the tracks 21 and 24, or by movement of the set constituted by the borne element and the support 4 with respect to the support 10, by rolling of the roller 14 and 15 on the tracks 9 and 20. If the borne element undergoes a stress in a different direction from X and from Y, the movement of this element with respect to the support surface 12 occurs at the same time through rolling of the rollers 14 and 15 and of the rollers 17 and 18. In all cases, the horizontal translation can only occur with a vertical movement of the upper part, hence of the borne element. The mass of the borne element is countered by gravity in the vertical movement, which permits, with a judicious choice of the shape of the profiles of the rollers paths, the selective combination of the acceleration and the displacement of the element with respect to the support. In all cases where the stresses originate in the fixed support, for example in the case of an earthquake causing large oscillations of the ground and of the support surface resting on the ground, the action of the support device to reduce the displacements and/or the accelerations of the borne element with respect to the support brings into play the same displacements as those which have been described in the case of a horizontal displacement of the borne element with respect to the fixed support. In all cases, the inertial forces in the vertical direction along an axis Z perpendicular to the axes Z and Y are transmitted integrally from the borne element to the bearer element, or conversely. In this case, neither the displacements nor the accelerations are therefore attenuated by the device according to the invention. In reality, in the case of an assembly rack for nuclear reactors, these racks are constituted by juxtaposed modular elements, and each of these modular elements is placed and supported on four devices of the type described. The reaction of the whole of the support device constituted by four elementary devices is similar to that of the elementary system itself. The invention is not limited to the embodiment which has just been described. Thus it is possible to conceive the use of any number of rollers in each of the upper or lower sets of the support device. These different rollers can be arranged with a fixed difference between centers by means of a junction bar connecting their axles, or they can be arranged freely individually or in partial groups, by provision of a special shape of the bearing tracks holding the rollers in spaced positions. The roller tracks can be attached to the support parts or machined directly in the the support parts. The rollers themselves can be produced in monoblock form or include several parts threaded onto the same axle. It is also possible to intercalate, between the lower support part resting on the fixed support and this fixed support, mechanical or hydraulic supporting and regulating means enabling the horizontality of the set of lower rollers to be regulated. Finally, the device according to the invention can find application outside of supports of racks for fuel assemblies in the storage pool of a pressurized water reactor. Thus it is possible to use these support devices each time that it is desired to avoid distortions of a supported structure which can undergo mechanical or thermal stresses. In all cases, the device enables the induced accelerations and the displacements to be minimized without the use of guidance locking or damping devices placed laterally with respect to the structure.