Spent fuel storage cask having basket with grid assemblies

Abstract

A cask for storing spent nuclear fuel after removal from a pool of water includes a container with a cylindrical cavity and a basket which is inserted into the container. The basket includes disk-like grid assemblies which provide spent fuel storage slots and which are coaxially mounted at spaced-apart positions, each grid assembly having a diameter that is slightly less than the one above it. If fuel assemblies are to be stored, hollow cells are affixed to one of the grid assemblies and positioned in the others by heat-conducting wedges which permit the basket and cells to expand at different rates. Rings which project slightly into the interior of the container are provided on the container walls, each ring being positioned to be in alignment with the periphery of a corresponding grid assembly after the basket is inserted into the container. Like the grid assemblies, each ring has a diameter that is slightly less than the ring above it, and moreover the diameter of each ring is slightly greater than the diameter of the corresponding grid assembly. These stepped diameters reduce the possibility that the basket might become jammed during the insertion process due to slight misalignment of the basket. After insertion, temperature changes expand the grid assemblies into pressing contact with the rings in order to transfer heat from the spent fuel to the container walls.