You should try the FatMan Ultra mod, which comes with a "Fat Man Extreme". Since completing the game (three times) I installed some of these frivolous things. The only way to survive firing the Fat Man Extreme is to do it over a hill so that it shields you when it detonates. Things tend to go cloudy for a while, since it basically uses the same model that detonating the bomb in Megaton uses.
[youtube]Ro9hVe6lH_M[/youtube]
Skip forwards to about 8:20...
If you haven't installed them, you simply must try out Fellout, BasicNeeds+Bottles and DC interiors. Also recommend Arefu Expanded, but it is a bit buggy. Enhanced Weather is also a nice mod with passing storms and even snow in the winter months, though this does go against the Fallout canon of a perpetual "Nuclear summer"...