Multiple studies estimated that anyone living within ten miles of Pennsylvania's Three Mile Island nuclear power plant, the site of a partial reactor meltdown in 1979, was exposed to a radiation dose that was less than that of a chest X-ray.
A chest X-ray delivers approximately 0.1 millisieverts of radiation. The typical person is exposed to about that much radiation every ten days in normal life.
The U.S. Nuclear Regulatory Commission reported that it, along with three other federal agencies, the state of Pennsylvania and several independent groups, studied the accident. Exposure was estimated at around 0.08 millisieverts or less. Other types of X-rays deliver greater doses of radiation—a spine X-ray delivers 1.5 mSv. "The actual release had negligible effects on the physical health of individuals or the environment," the NRC concludes.