I found an interesting blog that details the plans for nuclear war against Iran. This states that the planning is in the final stages. This story goes on to say that there is no considerable objections from the European Union, like there was with the war in Iraq.
Another story talks about CONPLAN 8022, which is a limited nuclear strike or strikes against targets where infantry troops would not be needed. The strike plan is offensive and can be carried out by presidential order. The explanation given by administration experts calls these "small" bombs, which would have a moderate effect on the environment. The effect of the bomb would not be discernible above ground, the radioactive fallout would be negligible, and the "collateral damage" caused to civilians would be minimal.