Patent Number: 047643366
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The de-activation pool of a nuclear station shown in FIG. 4 comprises a fluidtight inner covering 1 formed by metal sheets, for example of stainless steel, supported in a manner which will be described in more detail hereinafter, by a structure comprising a grid system of beams 2. The walls of this pool have a structure similar to that diagrammatically illustrated in FIG. 1. In the latter, the wall has in succession,from the exterior toward the interior of the pool, an outer part 3 formed from a hard and dense material such as, for example, concrete and defining a roughly planar inner surface, an inner part 4 formed from a hardenable material such as, for example, concrete poured into a space between said outer part 3 and an embedded lining comprising slabs 5 for example of fibrocement disposed in adjoining relation between the beams 2 so as to define with the latter a planar inner surface adapted to receive the metal sheets 6 of the fluidtight inner covering of the pool. The beams 2 are each fixed, before the pouring of the corresponding inner part, to the outer part of the wall by means of L-shaped fixing lugs 7 disposed on each side of the beam, preferably in an alternating arrangement, one of their branches being welded to the beam and the other being fixed, for example, by means of a bolt 8 screwed into said outer part 3 of the wall. These lugs moreover permit an adjustment of the distance of the beams from the outer part of the wall by compensating for unevennesses of its rough inner surface. Further, a spacer block 9, for example of rigid plastics material, is provided in contact with each fixing lug 7 on which it is maintained by means of a foil 10 which extends under the lug and the corresponding block. These blocks 9 each have a planar surface facing the interior of the pool and cooperate with a longitudinal flange 11 of the neighbouring beam extending in facing relation to and a distance from said planar surfaces of the blocks 9 so that a peripheral part 12 of reduced thickness of the slabs 5 can be inserted between the blocks and said flange of the neighbouring beam 2. The part 12 of reduced thickness of the slabs 5 is defined by a shoulder 13 whose thickness corresponds to that of the flanges 11 and facing toward the interior of the pool so that the inner surfaces of the slabs 5 and the beams 3 are contained in a common plane. The metal sheets 6 of the fluidtight inner covering of the pool bear on said inner surfaces of the slabs 5 of the lost coffering and of the beams 2. In this respect, each beam 2 defines a planar bearing surface 14 at the level of which two metal sheets 6 are supported and interconnected by one of their edges by a weld bead 15 which extends longitudinally along the beam 2 and roughly in the middle of the latter, the weld bead being connected to the bearing surface 14 of said beam 2. According to a first embodiment of the invention, the beam 2 illustrated in FIG. 1 comprises a first section element 16 and a second section element 17 each respectively having a cross-section roughly in the shape of a U and an omega the branches of which are roughly parallel to each other and of the same length. The first section element 16, incorporated in the concrete of the inner part of the corresponding wall, forms the outer part of the beam on which the lugs 7 are fixed and opens toward the interior of the pool. The second section element 17 is substantially narrower than the first and is fixed by the edge of each of its branches 18 to the bottom of the latter and thus defines three longitudinal channels. An inspection channel 20 having a closed cross-section, adapted to receive a device for the radiography of the welds of the sheets 6, is formed between the branches 18 of the second section element l7,and two draining channels 21 having a cross-section which is open toward the interior of the pool are formed on each side of the inspection channel 20 between said branches 18 of the second section element and the branches 22 of the first element 16. Further, the second section element 17 is fixed by the welding of two flanges 23 provided at the end of each of its branches 18, to the bottom 19 of the first section element 16, said flanges 23 extending outside the inspection channel 20. Further, the bearing surface 14 for the sheets 6 on the beams 2 is formed at the region of each of the latter by the surface of the intermediate part of the second section element 17 facing toward the interior of the pool, this bearing surface 14 being contained in the same plane as the inner surface of the flanges 11 provided at the end of each of the branches 22 of the first section element 16. This inner surface of the flanges 11 thus advantageously completes the bearing surface 14 by jointly supporting the sheets with the latter. With reference again to FIG. 4, it can be seen that access may be had to the vertical beams 2 from above the pool and that each of their lower endsis connected to a respective alignment of beams 2 disposed horizontally in the bottom of the pool. This connection may be achieved, as shown in FIG. 4, by means of a hollow T-shaped connector 26 which permits, on one hand, the communication between the channels of each vertical beam and those of the horizontally aligned corresponding beams and, on the other hand, the communication between the channels of the latter and a beam which extends outside the pool if this is possible. This connection may also be ensured by a bent beam, having a cross-section similar to that of the beam 2 described hereinbefore and bent longitudinally in an arc of a circle so that its end portions make a right angle therebetween. Further, in the region of each crossing of two alignments of beams 2, the latter are connected by means of a hollow X-shaped connector 27 so as to permit the communication between the channels of the beams which cross each other. This arrangement of the structure which supports the metal sheets of the covering 1 inside the pool, in a network of channels accessible from the exterior through the upper edges and optionally through the bottom of the pool, permits the introduction of a radiography device throughout the length of the inspection channels 20 and the piping for the leakage liquid drained by the beams, throughout the network. By way of a modification, the structure of beams may, of course, form a plurality of networks which are independent from each other. Such a beam 2 according to the invention permits, on one hand, radiographing the whole of the weld disposed on its bearing surface by means of the longitudinal inspection channel 20 having a closed cross-section, capable of receiving a suitable device, and, on the other hand, ensuring the draining of 100% of the leakages in the region of this weld owing to the presence of a longitudinal draining channel 21 provided on each side of the latter. Moreover, this beam perfectly performs its supporting function for the sheets 6 by providing a flat bearing surface 14 on which the latter may bear, and transmit to the concrete of the corresponding wall, through the beam, the pressure forces exerted by the water of the pool and the shear forces due to thermal stresses. Further, the presence of the flanges 11 of the first section element 16 advantageously increases the area of contact of the beam with the sheets while avoiding at the same time the piercing of the latter which would occur if they were directly applied against the end of straight branches. The parts of the second embodiment of the invention shown in FIGS. 2 and 3, which are distinguished from those of the first embodiment illustrated in FIG. 1, will now be described, the similar parts of these two embodiments carrying the same reference characters. The beam 2a shown in FIG. 2 is obtained directly by a cold drawing operation. This beam 2a differs from that previously described in that the second section element 17 is replaced by a second section element l7a which has in cross-section roughly the shape of an L and is in one piece with the first section element 17. A branch 24 of this second section element l7a is rigid at one end with the bottom 19 of the first section element 16 and extends in facing relation to and in the vicinity of a branch 22 of the latter so as to define therewith a longitudinal draining channel 2la having a cross section which is open toward the metal sheets 6 of the fluidtight inner covering of a de-activation pool. The other branch 25 of this L-section element extends transversely in a direction away from the draining channel 2la and defines a space between its free end and the corresponding branch 22 of the first section element 16, its surface facing toward said metal sheets 6 forming the bearing surface 14 of the latter on the beam 2a. Thus, a longitudinal inspection and draining channel 2Oa having an open cross-section and capable of receiving a device for radiographing welds, is formed between the branch 22 of the first section element 16 opposed to the draining channel 2la, and the branch 24 of the second section element l7a fixed to the first section element. By way of a modification (FIG. 3), the second section element 17a constructed separately from the first section element, includes a flange 23a which is welded to the bottom of the latter and extends in the draining channel 2la. Apart from the interest of directly obtaining a beam by a cold drawing operation, this beam 2a is advantageously narrower than the beam 2 of the first embodiment of the invention for a given width allowed for the respective visiting channel.