Patent Number: 044366930
Section: description

BEST MODE FOR CARRYING OUT THE INVENTION There is illustrated in FIG. 1 a canister 10 constructed in accordance with the present invention. The canister is standing vertically as if in a pool storage rack. The bottom plate P of the storage rack is shown, but the cell C (illustrated in FIGS. 2 and 3) is substantially cut away. The canister is of stainless steel and has a main body 12 of square cross-section and dimensions approximating that of a nuclear fuel assembly. The bottom of the canister 10 is closed by a bottom wall 14 (FIG. 3) and the upper end is closed by a cap 16 having a lifting bail 18. As previously explained, the canister will be substantially filled with nuclear fuel rods R and the filled canister may weigh, for example, 3,000 pounds. In order to store the filled canister in the cell C, which is designed for a load of 3,000 pounds, it is important to prevent impact in the event of an earthquake. In the present invention, this is achieved by means of lateral restraints at the top and at the bottom of the canister. Restraint at the bottom of the canister is provided by a central, lateral support pin 20 which extends downwardly from the bottom wall 14 of the canister and into the flow hole F of bottom plate P. The lower end of the canister is thereby restrained so as to prevent impact with the sides of the cell C. At the upper end of the canister, impact is substantially eliminated by reducing the clearance between the cap 16 and the wall of the cell C to a value sufficiently low that the upper portion of the canister cannot accelerate. This dimension, shown as x in FIG. 3, would be established in each case by a structural analyst but would probably be on the order of 0.030 inch with a maximum of 0.050 inch. The cap 16 must be tightly secured or sealed to the canister body 12. This may be done in a number of ways but, in the illustrated embodiment, is achieved by a pair of horizontally opposed locking pins 22 driven by a rotating drive member 24 through a linkage 26, all as illustrated in FIG. 4. In order to avoid obstruction by the bail 18, the drive member 24 is actuated by an offset, hexagonally headed, locking lug 28 through gears 30, 32. When fully extended, as illustrated in FIGS. 3 and 4, the locking pins 22 extend through openings 34 in the body 12 of the canister and into aligned openings 36 in the cap 16. Although the described construction substantially eliminates impact, there will still be some side loading at the top of the cell C. Accordingly, it may be desirable to strengthen the top of cell C by adding local reinforcement FIGS. 5 and 6 illustrate a modification of the invention whereby the need for maintaining a close tolerance gap at the top of the canister is eliminated. In this modification the cap 16 is provided with shimming means comprising tapered surfaces 40 adjacent at least two diagonal corners of the cap. At each such corner, there is inserted a double acting, right angle wedge 42. Each wedge has a body portion 44 which is connected to the cap 16 by means ob a bolt 46. Tapered surfaces 48 of each wedge engage the tapered surfaces 40 on the cap and the outer surfaces 50 of the wedge engage the sidewalls of cell C. After the loaded canister has been lowered into the cell C of the pool storage rack, the bolts 46 may be tightened, thereby driving the wedges downwardly so as to fixedly secure the upper end of the canister within the cell C. It is believed that the many advantages of this invention will now be apparent to those skilled in the art. It will also be understood that many variations and modifications may be made in this invention without departing from its spirit and scope. Accordingly, the foregoing description is to be construed as illustrative only, rather than limiting. This invention is limited only by the scope of the following claims.