The generation of power from nuclear materials has been well known in the art for many decades. The nuclear material, after a period of use for power generation, is incapable of generating the energy necessary and must be removed from its nuclear reactor. The major component of used nuclear material is spent nuclear fuel (SNF) rods. The transportation of such spent nuclear fuel rods has been a troubling problem over the decades and one that has not been solved entirely satisfactorily.
Spent nuclear fuel has the characteristic of emitting high amounts of radiation which is damaging to living tissue, particularly in humans. To handle the spent nuclear fuel safely, the fuel must be shielded with appropriate radiation shielding materials. Shielding materials, in general, are of a dense nature. To shield the radiation emitted from the spent nuclear fuel, shielded casks are used to maintain the exterior radiation levels at a sufficiently low level to prevent harm to personnel or the environment.
For transferring spent nuclear fuel to a transportation or storage cask, the current commercial industrial practice is an underwater or wet fuel transfer process which includes the step of submerging a cask into the nuclear fuel storage pool. Then, through the use of cranes and grappling hooks and the like, the spent nuclear fuel rods are transferred while still underwater into the submerged cask. The water acts as a radiation shield to protect personnel performing the transfer. The cask is then lifted from the storage pool, the interior of the cask is drained and dried, the outside is decontaminated and the cask is sealed.
An alternate method for the transfer of spent nuclear fuel rods is dry transfer. The current dry transfer system utilizes a transfer container to handle the spent nuclear fuel rods. A stand is placed under water in the spent nuclear fuel storage pool and the spent nuclear fuel rods are transferred to a position within the stand while still under water. The transfer container is landed on the stand and the bottom of the transfer container is opened by operating a translating gate. Then, a single spent fuel rod is raised through the bottom of and into the transfer container. This process is repeated to load the transfer container. Then, the transfer container is sealed by closing a translating gate and the transfer container is transported to a discharge stand. The transfer container is seated on the discharge stand and the translating gate is operated to open the bottom of the transfer container. A single spent fuel rod is lowered out of the transfer container and into a transportation cask located in the discharge stand. This process is repeated until all the spent nuclear fuel rods are removed from the transfer container and placed into the cask. Such method is disclosed in commonly assigned U.S. Pat. No. 5,319,686 to Pizzano et al, which patent is incorporated in its entirety herein by reference.
The wet fuel transfer process utilizes casks which are too large to be handled at many fuel storage sites because of constraints on existing lifting and handling resources. In addition, the wet fuel transfer process requires the exterior of the submerged cask to be cleaned or decontaminated to remove radioactive particles which increases the process time and the possible exposure of operating personnel to radiation and radioactive contamination.
The current dry fuel transfer process requires personnel to be located atop the transfer container to manipulate fuel handling tools and the like. Consequently, to protect the personnel atop the container, the transfer container must provide adequate shielding of the radiation being emitted by the spent nuclear fuel rods. This in turn increases the weight of the transfer container and its exterior dimensions which prevents its use at some fuel storage sites with limited lifting and handling capabilities. Also, grapple actuating tools penetrate the transfer container which hinders containment of any potential radioactive off-gases in the transfer container. In addition, the transfer container is only capable of raising or lowering one spent nuclear fuel (SNF) rod at a time. During the raising process, the SNF rods are not constrained from lateral motion after they are removed from the loading stand and prior to entering the transfer container. Also, during the lowering process, the SNF rods are not constrained from lateral motion after they are lowered from the transfer container and prior to entering the storage or transportation container.