The biggest impact would be economic
People having been convinced by the environmental movement for years that ANY level of radiation is hazardous, cleanup costs might indeed be astronomical.
In a city environment, people who were more reasonable about radiation and its actual effects may be able to simply wash the surfaces of most buildings and streets, washing the crap into the storm drains and oceans where it would dissipate with little real harm to the environment. This would not, of course, be acceptable to those who believe the Radiation As Evil Spirit paradigm.