whocares, you can't just go out and BUY a nuke, but private corporations do indeed own them. They build them and refurbish them for the Government. There are also several nuclear power plants out there that are in private (deregulated power company) hands. For examples of this kind of thing, look at:
http://www.brook.edu/fp/projects/nucwcost/sites.htm
Nuclear materials aren't that hard to come by in trace amounts, the main thing is expense. IIRC, you can buy tritium on the open market, and lots of people own trace amounts of it (for example, in watches and weapons sights) . For any kind of volume, there are serious regulations to go through, but it certainly can be done if you've got the resources for it.