Patent Number: 054066018
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, it is seen in FIG. 1 that the invention is generally indicated by the numeral 10. Transport and storage cask 10 is generally comprised of cask body 12, and basket 14. Cask body 12 is formed from stainless steel in the preferred embodiment. As seen in FIG. 1, cask body 12 is closed at one end and provided with suitable shield and seal means at the opposite end. The interior diameter of the upper end of cask body 12 is slightly larger than the remainder of the interior of cask body 12 to receive shield plug 16. This helps to prevent radiation leakage through the upper end. Shear ring segments 18 are positioned on top of shield plug 16 and are received in a notch 20 provided around the inner circumference of cask body 12. Shear ring segments 18 prevent operating and accident loads from being transferred to inner lid 22 which is positioned immediately above shield plug 16. Inner lid 22 is provided with a groove around its lower end necessary to fit around shear ring segments 18. Inner lid 22 may be seal welded to the inner circumference of cask body 12 as indicated at numeral 24. Outer lid 26 is fastened around its circumference to cask body 12 by bolts or studs 28. A replaceable metal O-ring 30 may be placed between outer lid 26 and the end of cask body 12 to provide an outer seal. Lifting bales 32 are provided as necessary on the exterior of cask body 12. Basket 14, best seen in FIG. 2, is formed from multiple layers of rowed carbon steel plates 34. Plates 34 have complementary shapes and partial hex grooves machined therein such that complete channels 36 for the fuel cells are formed when plates 34 are mated for insertion into cask body 12. Channels 36 are illustrated as being hexagonal but may be of any suitable shape depending on the material to be transported or stored. Plates 34 have a narrowed diameter 38 at each end and at intervals spaced apart along their length. Bands 40 are attached to each other by bolts 41 around plates 34 at each narrowed circumference point 38 to hold plates 34 in their assembled positions. The flat mating surfaces of plates 34 are machined to provide a close fit to prevent radiation leakage between plates 34. However, plates 34 may also each be provided with complementary grooves along their length to form a channel 42 between each plate sized to receive a locating key 44 that extends the full length of the plates. Each locating key 44 serves the dual purpose of holding the plates in alignment during assembly and blocking radiation from leaking between the mating surfaces at the plate junctions. Means for centering basket 14 in cask body 12 to maintain a steady state gap between the interior of cask body 12 and basket 14 are provided on cask body 12 and basket 14 in the form of centering keys 46. In the preferred embodiment, female key ways are provided at the lower end of basket that are designed to receive male keys on the inside lower end of cask body 12 while male keys are provided at the upper end of basket 14 and female key ways are provided at the upper end of cask body 12. The centering keys at the lower end of cask body 12 and basket 14 are preferably sized such that they engage basket 14 during installation in cask body 12 before the centering keys at the upper end engage. This provides for automatic location of the upper centering keys. In use, spent nuclear fuel is loaded into fuel cell channels 36 and shield plug 16, inner lid 22, and outer lid 26 are installed. Basket 14 and cask body 12 both undergo thermal expansion due to thermal radiation from the spent fuel that results in the gap between them remaining constant. During a fire transient, cask body 12 will absorb heat from the fire and undergo thermal expansion. However, due to the gap between cask body 12 and basket 14, little or none of the absorbed heat will be transferred across the gap and the gap will enlarge due to thermal expansion of cask body 12. Although the elevated temperature of cask body 12 from the fire precludes radiation of waste heat from the spent fuel, it has been determined that the peak fuel temperature will not occur until over twelve hours after the onset of the fire transient. The present invention thus provides a storage cask for spent nuclear fuel that is capable of withstanding normal operating and accident loads during transportation and normally expected fire transients. Because many varying and differing embodiments may be made within the scope of the inventive concept herein taught and because many modifications may be made in the embodiment herein detailed in accordance with the descriptive requirement of the law, it is to be understood that the details herein are to be interpreted as illustrative and not in a limiting sense.