A quick Google search shows it already has been done => https://www.youtube.com/watch?v=ra7YbBvbRYQ
Had drones existed in 1986 and deployed to take close photographs of disaster, would it have been safe to access that drone after it returned?
Quote from wikipedia:
"Equipment assembled included remote-controlled bulldozers and robot-carts that could detect radioactivity and carry hot debris. Valery Legasov (first deputy director of the Kurchatov Institute of Atomic Energy in Moscow) said, in 1987: "But we learned that robots are not the great remedy for everything. Where there was very high radiation, the robot ceased to be a robot—the electronics quit working.""
They've tried to put drones into Fukushima, attempts so far have been unproductive one way trips. Not all of that is the radiation killing stuff, apparently the geometry to be navigated has some pretty narrow passages as well.
You can see robots being used to clear off debris here: https://youtu.be/ezohqY-vg4s?t=57m43s