Spent nuclear fuel can be stored in reservoirs of water referred to as a spent nuclear fuel pool. Spent nuclear fuel assemblies can be immersed or stored in the spent nuclear fuel pool until such time as appropriate thermal and/or radioactivity conditions have been met, at which the assemblies can be transferred into transport and/or dry storage systems for off-site storage. Spent nuclear fuel assemblies are often comprised of an elongated assembly with a rectangular or other shaped cross section. As a spent nuclear fuel pool reaches capacity, it can be desirable to remove spent nuclear fuel assemblies and transfer one or more assemblies to on-site or off-site storage. On-site or off-site storage of spent nuclear fuel can involve placing spent nuclear fuel assemblies in a storage cask and/or transport cask that is hardened against accidents that may occur during storage or transport.
Included are systems and methods for storing spent nuclear fuel. At least one embodiment of a method includes a method for storing spent nuclear fuel, comprising the steps of disposing a spent fuel basket in a spent nuclear fuel pool; loading at least one spent nuclear fuel assembly in at least one chamber of a spent fuel basket, the spent fuel basket having a plurality of chambers, each of the chambers adapted to receive a spent nuclear fuel assembly; loading the spent fuel basket in a spent fuel canister; and loading the spent fuel canister into a storage cask or a transport cask.
Also included are embodiments of a system. At least one embodiment of a system includes a spent nuclear fuel pool; a superstructure in the spent nuclear fuel pool, the superstructure having at least one supporting structure; and at least one spent fuel basket, the at least one spent fuel basket having a plurality of chambers, each of the chambers adapted to store a spent nuclear fuel assembly, the at least one spent fuel basket further configured to be received by at least one of a spent fuel canister and a transfer cask; wherein the at least one supporting structure of the superstructure is configured to accept the at least one spent fuel basket.
At least one embodiment of a system also includes means for immersing a plurality of spent nuclear fuel assembles; means for containing the plurality of spent nuclear fuel assemblies; means for securing the containing means in the immersing means; means for lifting the containing means; and means for inserting the containing means in a transport or storage means.
Other systems, methods, features, and advantages of this disclosure 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 and be within the scope of the present disclosure.
Many aspects of the present disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.
In the following discussion, a general description of systems and methods according to various embodiments of the present disclosure is provided, followed by a discussion of the operation of the same. Embodiments of the present disclosure relate to spent nuclear fuel storage and transport systems. More specifically, disclosed herein are novel approaches to the implementation of spent nuclear fuel pools that can increase the efficiency of storage and/or removal of spent fuel from such a pool.
A spent nuclear fuel assembly, in some embodiments, can comprise an elongated assembly with a cross section that is often square or rectangular, but that can have a cross sectional shape of any kind. In prior art systems, each spent fuel assembly can be stored in a metal tube having a cross section and length corresponding to the size of the spent fuel assembly stored therein. More than one of the above-described tubes can be stored in close proximity in the spent nuclear fuel pool, often being mechanically joined together as a rack system to form a rectangular and/or square array in a spent nuclear fuel pool dependent on the geometry of a particular pool in which they are disposed. A rack in a spent nuclear fuel pool comprises various hardware components installed in the spent nuclear fuel pool to contain the various tubes containing spent fuel assembles. A spent nuclear fuel pool can have numerous racks immersed therein until the spent nuclear fuel pool does not have the capacity to accept additional spent nuclear fuel assembles or thermal and other conditions of the spent nuclear fuel assembles make it appropriate for them to be removed from the pool and stored in dry storage systems. The rack structures are self-supporting and may be free-standing, although some spent fuel pools may be designed to anchor racks to the pool through the use of vertical or lateral mechanical means.
As a prior art spent nuclear fuel pool reaches capacity, the fuel assemblies in a spent nuclear fuel pool can be removed from the pool and placed in a dry storage system so that additional spent fuel assemblies that are used by a reactor can be immersed in the spent nuclear fuel pool until the spent fuel reaches appropriate thermal and/or radioactive levels such that it is appropriate for them to be removed therefrom.
Dry storage systems (termed “dry storage”) can be employed so that nuclear power plants can discharge and store spent nuclear fuel external to a spent nuclear fuel pool, thereby permitting continued operation of the power plants as the pool reaches its capacity and the plants are operated for extended periods of time with appropriate regulatory approvals. In one embodiment, a dry storage system can include concrete storage casks in which metal canisters having canister final closure lids that are welded closed or sealed with mechanical methods at the power plants following spent fuel loading are inserted. A storage cask or transport cask serves as an enclosure or overpack structure that provides mechanical protection, heat removal features, and radiation shielding for the inner metal canister that encloses the spent fuel. Such a cask can be designed for spent fuel storage as well as spent fuel transportation. Accordingly, transportable dry storage systems can be employed to facilitate storage of spent nuclear fuel at or near a site of a nuclear power facility as well as the ability to transport spent fuel in a transport cask to an ultimate storage or disposal facility following a period of at-reactor dry storage without having to remove the spent fuel from the dry storage system.
In most dry storage systems used with wet storage (e.g. immersion in a spent nuclear fuel pool), the spent nuclear fuel at the time of discharge from a reactor emanates high levels of heat and radiation due to radioactive decay, levels that are higher than dry storage systems can efficiently and economically store. Therefore, discharged spent fuel must spend some amount of time in the spent nuclear fuel pool until the radioactive decay and associated heat has reached levels sufficiently low so that dry storage technology can be used. This period of time for required storage in the spent fuel pool can be 3 to 10 years or more.
In dry storage systems, an inner structure is often employed to hold and geometrically position the spent fuel that is placed either into the metal cask or into the metal canister. In embodiments of the present disclosure, this inner structure, referred to herein as a spent fuel basket, can include various metal tubes or other structures that are mechanically joined together in close proximity as a unitized structure, the number and array thereof being determined by the desired size and weight of a metal canister and transport cask in which it is disposed.
Accordingly, in prior art spent nuclear fuel pools and dry storage systems, the design, size and geometry of storage racks in a spent nuclear fuel pool and baskets for a dry storage system are often incompatible due to differing design requirements. Dry storage systems, which can include a basket, canister and transfer cask so that the spent fuel stored therein can be transferred to a storage cask or a transport cask, are often configured to withstand more impact intensive and thermally threatening accident conditions than a prior art spent fuel pool rack designed for immersion with spent nuclear fuel assembles in a pool. Additionally, dry storage systems are often more structurally robust and more conservative with respect to analysis of a full range of structural, thermal, shielding, and/or criticality design basis events. Prior art racks for a spent nuclear fuel pool are often designed to withstand drop events onto the rack systems and of seismic events and the resulting excitation of the racks that could cause very modest rack impacts with each other and with the pool floor and walls.
Accordingly, the transferring of spent nuclear fuel assemblies into a dry storage system spent fuel basket can be a labor intensive and expensive process, which can require a great deal of handling of the assembles, increasing the risk of radiation exposure and/or accident. In prior art systems, each fuel assembly must be removed from a prior art wet storage rack in a spent nuclear fuel pool and inserted into a corresponding chamber in a dry storage basket. In other words, each of the assemblies may be required to be handled, one by one, until a dry storage basket is filled, at which time the basket is inserted into a canister, the basket-in-canister then inserted into a transfer cask, which is finally transferred to the storage overpack (e.g., a concrete dry storage cask) of the dry storage system. Additionally, in such a prior art system, upon closing, decontamination and/or decommissioning of a spent nuclear fuel pool, the wet storage rack hardware components installed in a spent nuclear fuel pool to provide structural support must undergo various decommissioning and decontamination procedures.
Accordingly, embodiments of the present disclosure are directed to spent fuel storage systems and methods that provide a more efficient loading and/or unloading of spent nuclear fuel assemblies in a spent nuclear fuel pool. Additionally, embodiments of this disclosure can reduce the labor required to remove a spent fuel assembly from a spent nuclear fuel pool and to store the spent nuclear fuel assembly in a dry storage and/or transport system. As a result, embodiments of the disclosure can reduce risk to personnel by reducing the number of times a spent nuclear fuel assembly must be handled individually when the assembly is eventually placed within a dry storage system. Furthermore, embodiments of this disclosure permit the use of baskets for both wet and dry storage, reducing the hardware (e.g., a full pool of wet storage racks) that must be purchased at the startup of the reactor and permitting only incremental purchases of baskets over time as pool storage demands require. Additionally embodiments of this disclosure can reduce decontamination and decommissioning costs by reducing the amount of hardware remaining in a spent fuel pool that must be disposed of at the end of life of a spent nuclear fuel pool and/or when various components must be replaced.
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In contrast to a prior art spent nuclear fuel pool, the depicted spent nuclear fuel pool is equipped with the capability to accept spent fuel baskets 102 that are configured to be compatible with a dry storage system. Accordingly, the spent nuclear fuel pool 100 is configured with a superstructure to support the spent fuel baskets and any additional equipment associated therewith. As described above, a spent fuel basket compatible with a dry storage system is often engineered to handle accident conditions that may occur during transport and dry storage. Consequently, a spent fuel basket 102 of the depicted embodiment may be engineered with additional support and/or protective structures relative to a prior art tube containing a spent fuel assembly in a prior art spent nuclear fuel pool. The spent fuel baskets 102 can also be mechanically coupled to one another by the in-pool superstructure to provide additional stability within the spent nuclear fuel pool 100 for wet storage design basis conditions and for handling of the spent fuel baskets.
Reference is now made to
Therefore, in one embodiment, the spent fuel basket 102 can be lifted with a lifting crane securing the basket 102 via one or more lifting lug and inserted into the spent fuel canister 206. In contrast to prior art spent nuclear fuel pools, each spent nuclear fuel assembly and/or metal tube containing a fuel assembly does not have to be individually lifted and inserted into a basket within a canister in the transfer cask for movement to a dry storage system when the assembly is designated for removal from the pool, thereby reducing the labor cost as well as exposure and accident risks associated therewith.
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It should be emphasized that the above-described embodiments of the present disclosure are merely possible examples of implementations set forth for a clear understanding of the principles of the disclosure. Many variations and modifications may be made to the above-described embodiment(s) without departing substantially from the spirit and principles of the disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims.
This application claims the benefit of U.S. Provisional Patent Application No. 61/242,480, filed Sep. 15, 2009, which is hereby incorporated herein by reference in its entirety.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/US10/48878 | 9/15/2010 | WO | 00 | 4/26/2012 |
Number | Date | Country | |
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61242480 | Sep 2009 | US |