Spent nuclear fuel – material that no longer releases enough of the right sort of energy to sustain a reaction in a power plant – is a pain in the neck. It has to be stored until its no longer dangerous, which takes hundreds or thousands of years, but nobody wants it stored anywhere near them, as nation’s inability to create a long-term storage facility demonstrates. So it’s usually stored on site at the power plant, either in pools of water (where, yes, you could safely go swimming ) or in “dry casks”.
Dry storage is generally safer in case of earthquake or other natural disaster, as the post-tsunami Fukishima meltdown demonstrated, but most places start with wet storage because it’s cheaper and easier to do.
Vermont Yankee, which ceased power production last year, has its spent fuel in wet storage but plans to move it to dry casks. The Brattleboro Reformer reports that the owner, Entergy, says it can start the move next year, two years earlier than planned, finishing by the end of 2020.
Seabrook Station uses dry cask storage.