A lot of people (at least in the south) know that uranium fuel was produced in Oak Ridge, Tennessee during World War 2. However, plutonium was also used in the bombs and this was all produced at the Hanford Site in Washington state. Hanford is now the most contaminated nuclear site in the US and the site of the biggest environmental cleanup. It is also the home of Trench 94, which can be seen in satellite pictures available on Google Earth.
The United States launched its first nuclear powered submarine, the Nautilus, in 1954. And it has built hundreds more since then. Many of them served out their lives and were decommissioned. The problem then was what to do with the old nuclear reactors they carried. The old fuel was removed for processing or storage, but this still left a big piece of radioactive metal. So what they do is put the submarine in dry dock, cut everything in front of the reactor off, then everything behind the reactor off, This leaves them with a big steel cylinder. They then attach a plate to the front and back, barge it up the Columbia River to the Hanford Site, and put it in Trench 94. So each of the barrels in Trench 94 is actually a piece of submarine. You can see the process on this web page. One guy has put together page about that numbers all the reactors and tells which submarine they came from (that picture is at the bottom of this page.
Most of the reactors have been there for a while, but supposedly the trench has been left open so that Russia can verify the submarines are scrapped. Plus they probably keep having to put more reactors there. These containers are supposed to last for 600 years.