How long does a nuke have a affect on a area? Well first let us talk about the nuke in general being made up of either Uranium, plutonium, or Thorium or fusion of hydrogen into helium. Usually Uranium in today's standards the explosion is 10 million times the energy produced by the combustion of a atom with coal. The two isotopes mostly used are U-235 and U-238 U-235 being used .7% of the times of nukes and U-238 being used 99.3%. Using these elements a nuke could last up to 4 months (Including Nuclear Waste). The nuke destroys the body or any living thing in it's radius (Cockroaches being a exception). Nuclear Power is not being only used on Bombs they have been used as Nuclear Plants. US had 109 that were certified and there were about 400 in the world. US gets 20% of it's electricity from Nuclear Plants and Means of Nuclear Energy.  

Photo Credit: http://en.wikipedia.org/wiki/File:Operation_Upshot-Knothole_-_Badger_001.jpg

Source: McCarthy, John. October 17th, 1995. Freqently Asked Questions about Nuclear Energy. http://www-formal.stanford.edu/jmc/progress/nuclear-faq.html