Since the US Nuclear Regulatory Commission recommended on March 16 that US residents who are within 50 miles of the damaged Japanese nuclear power plants should evacuate, there has been a lot of speculation as to why the NRC would recommend such a large evacuation zone when the guidance for the plume exposure pathway emergency planning zone in the United States is for an area approximately 10 miles in radius.
First, the NRC recommendation was based on specific US guidelines for radiation exposure and some sophisticated calculations of the possible radiation doses based on what is known or suspected to be happening at all of the Fukushima plants, so this NRC recommendation is very site-specific and incident-specific whereas planning guidance is based on a wide range of possible accident scenarios.
Secondly, the US guidance for emergency planning for commercial nuclear plants never established 10 miles as any kind of outer limit or maximum evacuation zone. Rather, the US guidance is designed to require highly detailed response plans and preparedness for a 10 mile radius zone since that area is at greatest risk and has the least amount of time to evacuate.
Specifically, the guidance states “In a particular emergency, protective actions might well be restricted to a small part of the planning zone. On the other hand, for the worst possible accidents, protective actions would need to be taken outside the planning zones.” It further states that “… detailed planning within 10 miles would provide a substantial basis for expansion of response efforts in the event this proved necessary.”
So, the NRC recommendation is not at all inconsistent with existing policy and guidance, especially considering that Japan is facing potentially severe accidents at four collocated nuclear power plants simultaneously. The 10 mile radius evacuation zone guidance effectively buys time for more detailed accident assessment that may ultimately expand the evacuation zone depending upon the specific event.
Author: Jack Long, Director of CBRNE Preparedness
 Criteria for Preparation and Evaluation of Radiological Emergency Response Plans and Preparedness in Support of Nuclear Power Plants (NUREG-0654/FEMA-REP-1), Section I.D.2
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