Patent Number: 062563637
Section: description

SPECIFIC DESCRIPTION As seen in FIGS. 1 and 2 a container 1 for spent nuclear fuel elements 2 (FIG. 5) has a massive and cylindrical side or outer wall 3 centered on a normally upright axis 21 and defining an interior 4. A floor plate 5 closes the bottom of the wall 3 and a cover 6 the top. The walls 4, floor 5, and cover 6 can include shielding materials, for instance steel with polyethylene shielding. A rack or basket 7 forming a plurality (here 32) of axially full length wells or passages 8 and 8a is itself formed as a stack of levels 15 each formed in turn by neutron-absorbing borated aluminum plates 9 and 9a joined together at slide joints 10 (FIG. 4). Snugly fitted in each of the wells or passages 8 and 8a is a square-section stainless-steel tube 11 holding the elements 2 and extending the full axial length of the interior 4 of the container 1. The plates 9a each extend diametrally between outer ends 14 that bear against an inner surface of the side wall 3 so as to be in good heat-transmitting contact therewith. These plates 9a, which are some 12 mm thick, subdivide the interior 4 at each level 15 into four quadrants 22, 23, 24, and 25. The plates 9 are some 8 mm thick and have lengths equal to two or three times the side length of the identical square-section wells 8 and 8a. They fit together at joints 16 where they are formed with half-width slots 17 that fit together to form the inner wells 8 that are wholly defined by the plate 9 and 9a and identical outer wells 8a of which at most two or three sides are formed by the plates 9 and 9a. Around the rack 7 the container 1 is provided with filler blocks 12 each made of cast aluminum in which are imbedded lead shield elements 13. Each block 12 has a part-cylindrical outer surface and an inner surface formed as one or two planar sides, so that together with the rack 7 they form the outer walls of the outer wells 8a. The rack 7 is assembled right in the side wall 3 one level 15 at a time, each level 15 being formed by two plates 9a, eight short plates 9, eight long plates 9a, and twelve filler blocks 12. Once complete, the square-section element-filled tubes 11 are slipped into place. As shown in FIG. 5 each such tube 11 carries a multiplicity of spent fuel rods 18 and is formed with an array of guide passages or tubes 19, here lying in a uniform array, each holding a respective absorber rod 20 to maintain the charge subcritical.