Patent Number: 056125437
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to the present preferred embodiments of the invention as illustrated in the accompanying drawings. In accordance with the present invention, there is provided a basket for transporting, storing, and containing nuclear fuel assemblies having an assembly of sleeves with a plurality of sleeves arranged in a uniform pattern and secured within a cylindrical shell. Each of the plurality of independent sleeves being sized to secure and contain a fuel assembly. A plurality of alternating sleeves of the plurality of independent sleeves are configured to include an angular shaped separator element secured to each corner of each of the plurality of alternating sleeves. A sheet of neutron absorbing material is positioned between each of the plurality of alternating sleeves for maintaining fission reactions within the basket below a critical level necessary to sustain a fission reaction. A support element for positioning and securing the plurality of independent sleeves is secured within the cylindrical shell. A bottom plate is secured to the bottom of the cylindrical shell providing vertical support for the plurality of independent sleeves. A shield lid is secured to the cylindrical shell and includes a plurality of disc elements and an access port for selective entry into the basket and a lid element is secured to the shield lid and to the cylindrical shell. The lid element including an access port for selective entry into the basket. In FIG. 1, the multi-purpose sealed boiling water reactor fuel basket 10 is shown with shell 12 having a top end 14, a bottom end 16, an outer wall 18 and an inner wall 20, according to a preferred embodiment of the invention. Shell 12 is preferably cylindrically configured but may be provided in other geometric configurations if desired, such as circular, square, rectangular, or the like. Basket 10 is preferably composed of a durable, resilient, non-corrosive material such as steel or steel alloys, and is typically shipped or transported in a transportation, storage, or shipping cask commonly used in the art. As seen in FIG. 1, basket 10 includes an assembly of independent sleeves 22 comprising a plurality of independent sleeves 24. Sleeves are preferably configured having a square cross section and positioned and secured in a uniform pattern inside shell 12 which is preferably cylindrically shaped. Each sleeve 24 is preferably sized and shaped to contain one boiling water reactor fuel assembly 48, however, in alternative embodiments fuel assemblies for different reactor types may be accommodated. Preferably, alternating sleeves 24 are provided within angular-shaped separator 26, best seen in FIG. 3. Separators 26 are preferably secured to each of the four corners of a sleeve by welding separator 26 to each of the four corner of sleeve 24. Separators 26 provide a means to maintain a uniform space between adjacent sleeves. Positioned between separators 26 are sheets of neutron absorbing material 28 which serve to maintain fission reactions within basket 10 below a critical level necessary to sustain a fission chain reaction. The sheets of neutron absorbing material 28 are positioned and secured along the sides of each sleeve 24 by fastening means such as thin strips of steel 30 or other durable, resilient material such as steel alloy located intermittently along the length of the sleeve. The sheets of neutron absorbing material may comprise materials such as boron-carbide, aluminum powder, aluminum alloy, or the like. The steel strips 30 are preferably welded to separators 26 along each edge of the sleeve to hold the sheet of neutron absorbing material 28 in position. Referring now to FIG. 2, independent sleeves 24 are preferably positioned and held in place within basket 10 by a support element means preferably comprising a support structure with two separate plates 32 and 34 preferably composed of steel, steel alloy, or other durable resilient material. Plates 32 and 34 are positioned in and fill a gap between the inner wall 20 of cylindrical shell 12 and the perimeter of sleeve assembly 22. As seen in FIG. 2, plates 32 and 34 are preferably installed at multiple locations around the inner perimeter of basket 12. Plates 32 and 34 bear against the sleeves 24 and the inner wall 20 of cylindrical shell 12, however, they are preferably not attached by any fastening means to either. In FIG. 1 a bottom plate 36 is shown and is preferably welded to cylindrical shell 12 providing vertical support means for sleeves 24 and support plates 32 and 34 best seen in FIG. 4. Bottom plate 36 is preferably composed of a durable, resilient, non-corrosive material such as steel, steel alloy, or the like, and may be secured to cylindrical shell 12 by welds or other mechanical fastening means. Referring now to FIGS. 1 and 5, a shield lid 38 and structural lid 40 are shown installed on basket 10. Shield lid 38 provides shielding from radiation emanating from fuel assemblies contained in sleeves 24. Shield lid 38 is preferably composed of a plurality of steel disks 39 welded together and which preferably sandwich a section of the sheet of neutron absorbing material 28. Structural lid 40 is preferably a thick steel disk configured for attachment of hoist rings used to lift basket 10 after it has been loaded. Both shield lid 38 and structural lid 40 are preferably welded to cylindrical shell 12 and have access means, preferably penetrations 42, best seen in FIG. 5, for draining basket 10, vacuum drying basket 10, and backfilling basket 10 with helium after shield lid 38 and structural lid 40 are installed. Penetrations 42 may be apertures or bores and are preferably sealed using multiple welds once the helium backfill process has been completed. Shield lid 38 is preferably supported during its installation by a shield support ring 44. In operation and use basket 10 is extremely versatile, reliable, and may accommodate a large number of boiling water fuel assemblies, preferably sixty-one, while meeting the stringent requirements established by regulatory authorities both in the United States and abroad to ensure safety during the storage or transportation of fuel assemblies. Basket 10, when contained within a cask, is designed to withstand a wide variety of environmental hazards including earthquakes, floods, tornadoes, and various other accidents such as vertical drops on unyielding surfaces and the like. The basket shell, lid, and supporting structures are such that forces imposed on the contained fuel assemblies 48 during such hazardous conditions or accidents are maintained below those that would cause failure of the basket. Cylindrical shell 12 with welded end plates 36 and lids 38 and 40 provide ample support to sleeves 24 during and shock, accident or other stresses, thereby preventing distortion and maintaining stresses in the sleeves within acceptable limits. Basket 10 may be subjected to temperatures which vary across the basket internals or temperature gradients. The unique configuration of basket 10 and its internal supports provide the basket components with the capability to withstand the effects of various forces imposed on the basket, such as those from a drop event, without constraining the basket such that temperature gradients cause additional stresses in the basket components. Basket 10 is configured to adequately dissipate heat generated by contained fuel assemblies 48. Basket 10 maintains temperature in the fuel assembly region below the level at which long term degradation of the assemblies could occur. Basket 10 provides a means to maintain fission reactions within the basket at a level which is significantly below the critical level necessary to sustain a fission chain reaction. This is achieved through the use of the sheet of neutron absorbing material 28 operably positioned between adjacent sleeves 24 in basket 10. Basket 10 is specifically designed and constructed to minimize radiation exposure to plant workers and to the general public when the basket is loaded with fuel assemblies and is contained within a transportation, shipping, or storage cask. As is evident from the above description, basket 10 may be provided composed of a variety materials used to construct various parts of the basket without jeopardizing or limiting the ability of the basket to meet the applicable regulatory criteria. For example, cylindrical shell 12 may be constructed of carbon steel, stainless steel, or other metallic alloys. Sleeves 24 may be composed, for example, of carbon steel, stainless steel, or other metallic alloys. Additional advantages and modification will readily occur to those skilled in the art. The invention in its broader aspects is, therefore, not limited to the specific details, representative apparatus and illustrative examples shown and described. Accordingly, departures from such details may be made without departing from the spirit or scope of the applicant's general inventive concept.