System and method for transferring spent nuclear fuel from a spent nuclear fuel pool to a storage cask

#This invention relates to the field of transporting and storing spent nuclear fuel and specifically to transferring spent nuclear fuel from a spent nuclear fuel pool to a storage cask.

#In the operation of nuclear reactors, it is customary to remove fuel assemblies after their energy has been depleted down to a predetermined level. In the commercial nuclear industry, fuel assemblies are typically an assemblage of long, hollow, zircaloy tubes filled with enriched uranium. Upon depletion and subsequent removal, spent nuclear fuel is still highly radioactive and produces considerable heat, requiring that great care be taken in its packaging, transporting, and storing. Specifically, spent nuclear fuel emits extremely dangerous neutrons and gamma photons. It is imperative that these neutrons and gamma photons be contained at all times.

#In defueling a nuclear reactor, the spent nuclear fuel is removed from the reactor and placed in a canister that is submerged in a spent nuclear fuel pool. The pool facilitates cooling of the spent nuclear fuel and provides radiation shielding in addition to that which is supplied by the canister. However, the canister alone does not provide adequate containment of the radiation. As such, a loaded canister cannot be removed or transported from the spent nuclear fuel pool without additional radiation shielding. Because it is preferable to store spent nuclear fuel in a “dry state,” the canister must eventually be removed from the spent nuclear fuel pool. As such, apparatus that provide additional radiation shielding during the transport and long-term storage of the spent nuclear fuel are necessary.

#FIG. 1 is a perspective view of a prior art transfer cask having a retractable door assembly.

#FIG. 2 is a perspective view of a prior art transfer cask having a retractable door assembly placed atop a storage cask with a canister of spent nuclear fuel being lowered from the prior art transfer cask into the storage cask.

#FIG. 3 is a perspective view of an embodiment of the transfer cask of the present invention, a transfer cask having a sealable bottom lid.

#FIG. 1 illustrates a prior art transfer cask 10 having cylindrical body 11 and a retractable door assembly 12. In order to shield the environment from the radiation emitted by a canister of spent nuclear fuel once it is placed within cavity 13, cylindrical body 11 is typically constructed of a gamma absorbing material such as lead and a suitable hydrogenous material. Retractable door assembly 12 comprises rectangular compartment 14. Rectangular compartment 14 forms space 15 in which retractable plates 16, 17 (FIG. 2) are located. Prior art transfer cask 10 further comprises cask lid 18 having lid hole 19.

#Referring to FIG. 2, once prior art transfer cask 10 is loaded with a canister 20 of spent nuclear fuel, transfer cask 10 is positioned above and set atop storage cask 21. This is done in order to facilitate the transfer of canister 20 from transfer cask 10 to storage cask 21. However, as discussed in detail above, prior art transfer cask 10 is not secured to storage cask 21 during this process, transfer cask 10 merely rests atop storage cask 21. Once prior art transfer cask 10 is placed atop storage cask 21, retractable plates 16, 17 are moved to an open position. Retractable plates 16, 17 comprise rollers that require lubricant in order to move properly. Moving retractable plates 16, 17 to the open position results in an unobstructed path being formed between the cavity of transfer cask 10 and the cavity of storage cask 21. As such, canister 20 can be lowered by a crane 22 from prior art transfer cask 10 into storage cask 21 for permanent storage. As discussed above, prior art transfer cask 10 has a number of deficiencies.

#FIG. 3 illustrates an embodiment of the present invention, transfer cask 30 having sealable bottom lid 32. Transfer cask 33 comprises a cylindrical body 31, circular bottom lid 32, and cask lid 33. Cask lid 31 comprises cavity hole 34 and a plurality of cask lid bolt holes 43 circumferentially located around cask lid 31. Cavity hole 34 facilitates access to cavity 40 (FIG. 5) which is necessary to perform certain canister transfer operations. Cylindrical body 31 comprises bottom flange 35, top flange 36, drain valve 37, fill hole 38, and crane handles 39. Bottom flange 35 comprises a plurality of bottom lid bolt holes 41 and a plurality of mating device connection holes 42, both circumferentially located around bottom flange 35. For the reasons discussed below, mating device connection holes 42 are positioned closer to the outer perimeter 55 of bottom flange 35 than bottom lid bolt holes 41.