Considering MAD existed and most nukes would have been dropped on the US and USSR, not Germany, I don't think that's the issue. We and the russians had far more to worry about than the germans. Of course MAD pretty much ensured a 0% chance of nuclear war so really nothing to worry about. Nations truly worried about nuclear weapons develop them, not fight against them. Think about it.

Considering that Germany is an american vassal with significant russian influence, it's more likely political factions tied to US and Russia. US doesn't want Germany to develop nuclear energy because nuclear energy research is the same thing as a nuclear weapons research. A nuclear armed germany is pretty much an independent germany which is something no empire desires. Empire and freedom/independence/sovereignty don't mix. And russians don't want germany to develop nuclear energy because they want to sell more oil/gas to germany and gain more influence over germany/europe.