Patent Number: 
Section: description

FIGS. 1 and 2 generally depict a spent nuclear fuel assembly pool 10 defined by a floor 12 and sidewalls 14 and containing water up to a water line 16. The pool 10 contains existing first spend nuclear fuel assembly storage racks 20 that are supported by structural members such as support pads 21 on the floor 12 of the pool 10. The storage racks 20 may alternatively be supported via a frame (not shown) that in turn is supported by the floor 12. Floor supported storage systems are discussed in U.S. Pat. No. 5,152,958 and the patents it references, including U.S. Pat. Nos. 4,889,681; 4,666,660; 4,336,103; 4,069,923 and 4,029,968, which patents are incorporated by this reference for their disclosures of the structures of such systems. As is discussed in U.S. Pat. No. 5,152,958 and referenced patents, including U.S. Pat. No. 4,287,426 and West German Patent No. 29 43 455, the spent nuclear fuel assembly storage racks may be wall supported instead of floor supported. These patents are incorporated by this reference for their disclosures of the structures of such systems. In order to increase the capacity of the spent fuel assembly fuel pools such as pool 10, one or more second spent nuclear fuel assembly storage racks 30 with support pads 31 are installed in the pool 10 over the previously installed racks 20 as shown in FIG. 1. Importantly, the second storage racks 30 are structurally supported independently of the previously installed storage racks 20. Thus, the second storage racks 30 are not directly or indirectly supported by the support pads 21, support frames or other structural support members supporting the previously installed storage racks 20. Advantageously, the second spent nuclear fuel assembly storage racks 30 may be installed while spent nuclear fuel assemblies are being stored in the previously installed racks 20. As shown in FIG. 1, the second storage racks 30 may be supported by a platform 32 suspended from hanger rods 34 extending from hanger brackets 36 bolted or otherwise mounted to the existing operating deck 38 of a spent fuel pool 10. Advantageously, the second storage racks 30 and their structural supports may be designed to support the static load of the second storage racks 30 and the dynamic loads of earthquakes independently of the previously installed storage racks 20. FIG. 2 shows an alternative two tier storage arrangement where one or more second spent fuel assembly storage racks 30 having support pads 31 are supported on a platform 32. The platform 32 is supported by support members such as floor supported posts 42 that are structurally independent of support pads 21 or other structural members supporting the spent fuel assemblies 20 of the lower tier. The platform 32 may be stationary or, alternatively, may be horizontally mobile (not shown). The previously referenced U.S. Pat. No. 5,152,958 discloses structure of a horizontally mobile spent nuclear fuel assembly storage platform or bridge. As depicted in FIGS. 1 and 2, the spent nuclear fuel assemblies 30 of the upper tier, like the spent nuclear fuel assemblies 20 of the lower tier, are stored while vertically oriented, i.e., the lengths of the tubes in the assemblies extend vertically. Because fuel assemblies are generally from about eight feet to about fourteen feet in length, the water level 16 of the pool 10 will be no more than about 10 feet above the top of the spent fuel assemblies 30 of the upper tier in many existing spent nuclear fuel assembly pools. This depth is adequate to shield spent fuel rods that are at least about five years old. If additional shielding is desired, then additional shielding (not shown) may be provided over the top of the spent fuel assemblies 30. In the practice of the present invention, spent nuclear fuel assemblies are introduced into the spent nuclear fuel assembly storage racks 30 while vertically oriented. Accordingly, at least a portion of the spent nuclear fuel assemblies will be raised above the water level 16 in plants where the fuel assemblies are longer than about ten feet in length. In some practices, the spent nuclear fuel assemblies may be entirely raised above the water level 16 of the pool 10. FIG. 3 depicts a handling assembly 52 in the process of introducing a vertically oriented spent nuclear fuel assembly 50 into an upper tier spent nuclear fuel assembly storage rack 30. The handling assembly 52 may be similar to the design of assemblies carried by refueling machines to introduce fuel assemblies 50 into a reactor pressure vessel (not shown). See, e.g., U.S. Pat. Nos. 4,511,531 and 4,929,413, which show telescoping gripper assemblies carried by refueling machines. Thus, the handling assembly 52 may include a handling tool with air-operated gripper fingers (not shown) disposed in an elongated gripper tube 54 also having an integral shield plug (not shown) disposed above the fingers. The gripper tube 54 may be telescoping operated within a mast 56 by an electric winch 58 to raise and lower the fuel assembly 50 between a position in the storage racks 20 and 30 and a position in a vertically oriented transfer cask 62 mounted on the mast 56. Advantageously, the transfer cask 62 will provide radiation shielding for the spent fuel assembly 50 when near to and above the water surface 18. A support platform 60 supports the gripper tube 54, mast 56, winch 58 and transfer cask 62. The support platform 60 may also support an air hose reel 64 for the handling tool and an electric reel 66 for the electric winch 58. The platform 60 may be suspended over the spent fuel pool 10 via a cable 68 from the generating plant""s overhead spent fuel pool crane (not shown). While a present preferred embodiment of the present invention has been shown and described, it is to be understood that the invention may be otherwise variously embodied within the scope of the following claims of invention.