We have no idea what kind of warhead it was, what yield it was, and we don't really know how high they were. There would be no fallout in the conventional sense of irradiated soil and particulate matter, since there's no soil and no debris except for a bit of skin off Superman. The physical components of the missile would be scattered to the four winds, but the quantity of radioactive material that comprised the missile's body and the materials that failed to fuse or divide in the warhead itself is negligible on a planetary scale.
Direct radiation effects 200km up in the sky won't amass to anything by the time it hits the ground.
The inverse square law applies since it radiates out in a perfect sphere. Not only is over half of the energy shooting straight out into space or going sideways into the other parts of the upper atmosphere, but the stuff pointing down gets weaker at an extremely rapid rate. Taking the intensity at 10m distance as the baseline, at 20m the intensity is only 1/4 as strong, at 30 meters the intensity is 1/9 as strong, at 40m the intensity is 1/16 as strong, and so on.
Since the yield is unknown, and this might only have been a 2kt weapon designed for tactical work against Kryptonian space ships rather than a 1mt citybuster, we can't really say how big of a boom it would be making. That the generals involved seemed to think it was ok is basically all we need to know as an audience. This is the stuff usually reserved for reference manuals and visual cross section books.