I agree about the nukes but there are Russians available to do maintenance - for a price. Thought Hiroshima was bigger but I'll believe 12.5 KT, I would still like about 30 if I was making a point. Especially a ground event.
30 Kilotons at 500ft to 1500ft would be devastating. Even a ground burst would be very destructive.
That said, I still have serious doubts about these kinds of stories not only because of what I know about nuclear weapons but because the same stories (with minor variations) have appeared every year since Sept. 11th.