More than you ever wanted to know about Nuclear Fuel
Each of the two Reactors at North Anna contains 157 fuel assemblies. Each fuel assembly consists of 204 fuel rods, loaded with 328 ceramic pellets – so over 16 million pellets are used to generate heat to boil water and turn turbines to produce electricity.
Each pellet has the energy equivalent to 1800 pounds of coal. When the uranium has decayed so much that nuclear fission is no longer creating sufficient heat, Dominion “refuels” the reactor and replaces the fuel assemblies. [Source]
For the first 5-10 years they are stored in pools of water to dissipate heat and prevent them from melting.
When they are cool enough to be removed from the pool, a “dry cask” is lowered into the pool, the cool fuel rods are placed into the dry cask, all water and air is pumped out and replaced with inert helium, then the dry cask is welded shut.
The pool shown here is not that of North Anna. The 3 photos of Dry Casks are of the North Anna Installation.
As is visible in the photographs some casks are stood vertically and some are set horizontally in storage bunkers. Following are sketches of the structure of these radiological “safes”.
Site Storage, like North Anna’s is not unusual in the U. S.
Here is a link to the Study done to determine the suitability of the North Anna Site for storing the spent fuel. Although the analysis is beyond most people to evaluate, it appears not to have been a haphazard determination.