Many people appear to believe they explode far too much in Civ 4 currently, so to make them explode less do you make this number less or more. It surely must be to do with this figure in the buildingsinfo.xml.
"<iNukeExplosionRand>1000</iNukeExplosionRand>"
"<iNukeExplosionRand>1000</iNukeExplosionRand>"