NRC Changing Its Definition of “Background” Radiation?
by Chris Shuey, MPH.
Uranium Impact Assessment Program Director
Southwest Research and Information Center
This press release from the U.S. NRC, dated March 16, 2011, says that NRC believes it is “appropriate” for all Americans living within 50 miles (80.5 kilometers) of the Fukushima plants to evacuate. Unless there’s new recommendations from the Japanese government, I believe this is a greater evacuation distance than previously announced.
The suggested evacuation distance is based on “protective action recommendations” that are triggered when whole body radiation doses exceed 1 rem (10 milliSieverts) and doses to the thyroid exceed 5 rem (50 mSv), NRC said. The agency cited “[a]ttached…computer calculations” to support the recommendations, but there were no attachments to the press release.
You’ll note that NRC says background radiation from all natural and human-made sources is 620 millirems per year (0.62 rem/yr). On its web site, the NRC says about half of this background is from natural sources and the other half is from human-made sources, including medical uses of radioactive materials. This is the highest “background” radiation dose I have ever heard cited by a regulatory agency.