Patent Application
20060188054
The present invention relates to methods for transporting and canistering nuclear spent fuel.
The removal of spent nuclear fuel (SNF) from nuclear power plants and the transport of that spent fuel to an away-from-reactor facility for storage, disposal, or further aging (to reduce its heat content through radioactive decay) is a consideration within the nuclear fuel cycle in the U.S. Currently, the operation of a repository for spent fuel includes the transport of the spent fuel to the repository facility where the fuel is then removed from a cask and placed into a waste package for disposal or, alternatively, placed into a sealed canister for storage in a protective, passively cooled overpack for an additional period. This permits the heat content of the fuel to decrease through radioactive decay until the fuel is cool enough to be placed into a waste package for disposal. This latter process is called “waste aging.”
Typically, spent fuel is shipped from a nuclear power plant to a remote facility (repository or storage facility) in one of two configurations: as “bare” fuel, where individual fuel assemblies are placed into discreet locations within a transport cask (a “basket” structure) for later removal individually at the remote facility; or as “canistered” fuel, in which multiple assemblies are placed into a canister having an internal basket structure and welded closures, then shipped in the transport cask without a basket (the canister provides the same functions as the basket). If there is a preference for shipping the fuel in a “bare” configuration, then, at the remote facility, the fuel designated for aging must be removed from the transport cask, placed into a canister, sealed, and placed into a protective, passively cooled overpack. These canister closures are typically welded for the purpose of sealing.
The drawbacks of this approach are that the welding of the canisters at the repository includes the acquisition of costly welding equipment, along with special inspection and testing equipment. It also includes a special area designated for such operations. The welding further includes extensive time and personnel, making it costly and extending operations schedules. The welding process results in more personnel radiation exposure than other sealing methods. The waste aging canisters will need to be opened at some future date for spent fuel disposal; this will include the cutting of the welds on the closure lids and the disposal of the canister system as low-level waste after it is emptied.
Another approach is to ship the bare fuel to the remote facility in what are termed “dual purpose” casks, which are casks that are certified for both the storage and transport of the spent fuel contained therein. Dual purpose casks are very expensive, having design features for both storage and transport, and the licensing activities to certify the design for both storage and transport add to the cost of each system, as well. If the bare fuel is shipped to the remote facility in dual purpose casks, these casks can be taken from the transportation system and placed into storage at a spent fuel storage facility, without the need to unload the casks and transfer the spent fuel to a separate storage system. However, once in storage, these very expensive dual purpose casks cannot perform additional transport until they have been emptied of their current contents and returned to transport service.
Thus, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies.
Disclosed are methods for transporting and canistering nuclear spent fuel. In one embodiment, the method for transporting and canistering nuclear spent fuel comprises providing a canister that includes a mechanical closure for a canister lid and a container at a first or origin remote facility. The mechanical closure can be a bolted closure, a screwed closure, or any other form of mechanical closure that results in sealing. The canister containing the nuclear spent fuel is loaded into a transport cask without the canister closure and a transport cask is sealed at the first or origin remote facility. The transport cask containing the canister and nuclear spent fuel is transported to a second remote facility. At the second remote facility, the transport cask is opened and the canister lid to the container of the canister is installed using the mechanical closure to seal the canister after the canister is transferred to the second remote facility. The canister containing the spent nuclear fuel is placed into an overpack, which is stored at the remote facility.
As a further option, the canister lid is welded on the container of the canister to seal the canister after the canister is transported to the remote facility.
The invention has numerous advantages, a few of which are delineated hereafter, as merely examples.
An advantage of the invention is that there may be no costly welding or other inspection/testing capital equipment. There is no need for consumable supplies to support the welding operations (weld wire, gases, dye penetrant, etc.).
Another advantage of the invention is that no special location for welding is set aside and no special provisions for shielding, ventilation (HVAC), and utility services must be supplied for canister welding.
Another advantage of the invention is that there will be no need for certified canister closure welders, together with the administration of training, qualification/certification, and welding data/record services programs.
Another advantage of the invention is that the mechanical canister closure takes much less time and personnel cost to seal the canister.
Another advantage of the invention is that the personnel radiation exposure will be commensurately reduced.
Another advantage of the invention is that when the canisters with mechanical closures are reopened, the canisters, along with their lids, can be recycled for use again with other fuel. One of the waste materials will be the lid seals that are replaced and any materials from decontamination of the canisters for reuse. However, these waste volumes are substantially less than those that result from the disposal of the entire canister, should fuel be removed from a canister with a welded closure.
Another advantage of the invention is that in the long term, the canisters may also be incorporated directly into second-generation waste packages, thereby helping to reduce the cost of those packages and reducing the cost of repackaging the spent fuel.
Another advantage of the invention is that for waste aging applications, the method is much more cost effective because the capital cost of storage of such spent fuel in canister-based systems placed in concrete overpacks is only a fraction of the capital cost of the far more expensive dual purpose metal casks. The service of metal casks is best applied to transport of spent fuel, whether as bare fuel or canistered fuel.
Other systems, methods, features, and advantages of the present invention will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present invention, and be protected by the accompanying claims.
The present invention, as defined in the claims, can be better understood with reference to the following drawings. The drawings are not necessarily to scale, emphasis instead being placed on clearly illustrating the principles of the present invention.
Disclosed are methods for a canister that stores and transports spent nuclear fuel. In one embodiment, the method includes providing a canister that includes a mechanical sealed closure (e.g., bolted closure, or screwed closure) for a canister lid and a container to seal the canister. The nuclear spent fuel is loaded into the canister at the power plant. The canister containing the nuclear spent fuel is loaded into a transport cask and the transport cask is sealed at the power plant. It should be noted that the canister lid is not sealed on the container at the power plant. The transport cask containing the canister and nuclear spent fuel is transported to a remote facility. At the remote facility, the transport cask is opened and the lid to the canister is installed using the mechanical closure to seal the canister after the canister is transported from the power plant to the remote facility. The canister containing the spent nuclear fuel is placed into an overpack, which is stored at the remote facility.
Example apparatus, systems, and methods are discussed with reference to the figures. Although the apparatus, systems, and methods are described in detail, they are provided for purposes of illustration only and various modifications are feasible. The exemplary apparatus having a bolted closure as a mechanical closure for a canister lid and container is first discussed. After the exemplary apparatus has been described, examples of systems for storing and transporting spent nuclear fuel are provided, particularly a transport cask, a transfer cask, a transfer adapter and an overpack. After the exemplary systems have been described, examples of methods for storing and transporting spent nuclear fuel are provided.
Referring now to
In some embodiments, an outer lid 120 cooperates with an open end 117 of the canister so that a redundant seal of the storage system is provided. Preferably, the outer lid is retained in sealing engagement with the distal end of the canister by a hold-down member 122 (described in detail hereinafter). As depicted in
Referring now to
Referring now to
Once appropriately positioned with the retention recess, drive bolt 144 of the compression link may be driven so that a distal end 146 of the drive bolt is urged downwardly toward the closure lid. Preferably, although not required, that portion of the closure lid which is intended to receive or engage the distal end 146 of the drive bolt is configured with a hardened surface which is adapted to resist substantial deformation in response to engagement of the drive bolt. In some embodiments, the functionality of the hardened surface may be achieved by one or more bearing members or inserts 148. Such an insert may be formed of metal or any other suitable material.
In some embodiments, insert 148 may include a bolt-receiving recess 150 for properly positioning the distal end 146 of the drive bolt. So provided, once the bolt is driven so that the distal end of the drive bolt engages the insert, downward force of the bolt is transferred to the closure lid, thereby urging a seating surface 152 of the closure lid against a closure lid-receiving ledge 154. Additionally, in reaction to the downward force of the bolt, the outer retaining member 155 of the compression link is urged upwardly so that the engagement surface 132 engages the closure lid-retention surface 134, thereby retaining the closure lid in its locked or sealed position.
In order to facilitate a more secure sealing of the closure lid, some embodiments may incorporate a gasket 156 which is adapted to engage in a sealing relationship with the closure lid and the canister shell, such as by being received within a gasket recess 158 of the closure lid and engaging a surface defining the recess as well as seating surface 152 of the canister shell. So provided, engagement of the compression link with the closure lid and canister shell places axial, tensile force in that portion of the canister shell located between the closure lid-retention surface and the closure lid-receiving ledge, while exerting a compressive force on the closure lid. This is accomplished with the bolts of the compression links not being attached to or through the seating surface of the closure lid or the closure lid-receiving ledge of the canister shell.
Referring now to
Preferably, lid hold-down member 122 incorporates an upper ring 182 which is adapted to be received about the distal end of the canister shell and the outer lid, with an outer lid hold-down ledge 184 protruding from an inner surface of the ring. The hold-down ledge 184 is adapted to be received by the hold-down receiving recess 170 of the outer lid. A plurality of connectors 192, e.g., bolts, depend from the ring, with each of the connectors engaging a lid hold-down segment 194. Each lid hold-down segment is configured as an arcuate segment with an inner diameter which is appropriately configured so that each segment may be received about an exterior surface of the canister shell. In order to facilitate sealing engagement of the outer lid with the canister shell, each lid hold-down segment preferably incorporates an outer lid-retaining ledge 196 which extends inwardly from its respective segment. The aforementioned outer lid-retaining ledges are adapted to engage within a compression recess 198 formed in an outer surface of the canister shell. So configured, when the connectors are tightened, each lid hold-down segment is urged toward the ring, thereby causing the outer lid-retaining ledge 196 to engage the compression recess 198 of the canister and the outer lid hold-down ledge 184 of the ring 182 to engage the hold-down receiving recess 170 of the outer lid. Thus, when so tightened, the outer lid is held in compression against the canister shell.
It should be noted that the mechanism closure of the canister can also include a screwed closure as disclosed in U.S. Pat. No. 5,615,794, which is entirely incorporated by reference herein, as well as any other mechanical closure.
In block 212, the transport cask is opened and in block 214, the canister lid to the container of the canister is installed using the mechanical closure to seal the canister after the canister is transported to the remote facility via the transport cask. The step for installing the canister lid to a canister as shown in block 214 is further described in relation to
In block 232, a backing member is provided to be inserted between the closure lid and the compression link such that insertion therebetween urges the compression link radially outwardly from the closure lid. In block 234, a bearing member is provided to be inserted between a portion of the compression link and to engage the bearing member with the closure lid. In block 236, an exothermic material is inserted within the container prior to sealing the closure lid, wherein the exothermic material is SNF.
The foregoing description has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Modifications or variations are possible in light of the above teachings. The embodiment or embodiments discussed, however, were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly and legally entitled.
