Patent Number: 054066018
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention is generally related to the transport and storage of radioactive material and particularly to a cask that can be used for transporting or storing spent nuclear fuel. 2. General Background Nuclear reactors require periodic replacement of the nuclear fuel. Fuel removed from reactors in naval vessels and some land based commercial reactors must be transported to a storage site. In some instances, there may be storage room at the site of the land based reactor. The United States Nuclear Regulatory Commission sets standards that must be met for casks that are used to transport or store spent nuclear fuel. Due to the different conditions that may be encountered during transport and static storage, separate standards are set for transport casks and for storage casks. These standards are respectively set forth in 10 CFR 71 and 10 CFR 72. Shipping casks must be able to withstand shock loads during transport while storage casks must be able to withstand temperature transients such as a fire external to the cask without transmitting additional heat to the inside of the cask. As a result, it is common to have separate casks for transport and storage. This presents the need for additional work in the form of transferring the fuel from one cask to another once the shipment has arrived at the storage site. If there is not an immediate need for reuse of the transport cask, then the transport cask which has a radioactive interior after use must also be stored until it is needed again. SUMMARY OF THE INVENTION The present invention addresses the above problem in a straightforward manner. What is provided is a cask that can be used for both transport and storage of spent nuclear fuel. The cask body and basket are designed such that there is a gap between the cask body and basket. The basket is formed from multiple layers of rowed plates that cooperate with the cask body to provide the required radiation shielding, thermal, and structural requirements of 10 CFR 71 and 10 CFR 72. The plates have complementary shapes and partial hex grooves machined therein such that complete channels for the fuel cells are formed when the plates are mated for insertion into the cask body. The plates have narrowed diameter sections and are held together by bands around the circumference of the plates at these sections. Locating keys received in grooves between the plates extend the entire axial length of the basket to hold the plates in alignment during assembly and to block radiation leakage across the vertical gaps between the plates. Centering keys are provided at the upper and lower ends of the basket and cask body to provide a consistent gap between the basket and cask body. The gap expands during a fire due to thermal expansion of the cask body prior to thermal expansion of the basket and thus does not allow conduction of the external heat into the basket and fuel during an external transient temperature rise.