The US Environmental Protection Agency has drafted new guidelines to protect workers and the public in a radiological emergency.
Open for public comment, the latest draft is an update to EPA guidelines issued in 1992, with the main change being a broadening of scope beyond simply a nuclear power plant accident scenario. Today, the EPA wants America to be prepared for radiological emergencies at military facilties, nuclear fuel plants, in transport of radioactive materials or resulting from terrorist use of a dispersal device or even a crude nuclear weapon.
Radiological incidents are rare, and each one is different. Because of this, the broadening of EPA's scope has little effect on its three basic principles of response, which should: "prevent acute effects; balance protection with other important factors and ensure that actions result in more benefit that harm;" and to "reduce risk of chronic effects."
It is a "complex judgement," said EPA, to determine an appropriate response to a radiological emergency, particularly to find the right balance between potential effects of action by authorities against the threat posed by the incident itself.
One example of this judgement in practice was the decision to evacuate elderly and vulnerable people from Fukushima prefecture - an action that is now known to have directly lead to a number of deaths, whereas the risk from radioactivity was too low to have had any serious effect.
In terms of immediate response, EPA considers a projected dose of 10-50 mSv over four days to be enough to consider sheltering or evacuation. This would be a decision to be taken considering "the risks associated with the evacuation itself." Relocation should be considered for members of the public expected to receive doses of over 20 mSv in the first year, or 5 mSv in subsequent years.
In the first month, however, EPA said that the public could return to contaminated areas "for use of critical infrastructure" in areas where annual doses could be 20 mSv. For general tasks such as access to evacuated homes, return could be allowed in areas of 5 mSv annual dose areas.
These figures are highly conservative compared to the global average radiation dose from natural sources of 2.4 mSv per year, or, for example, the 9 mSv per year received by an airline crew working the polar route between New York and Tokyo.
In Japan, Fukushima residents are allowed to return for important tasks to areas with dose rates from 20-50 mSv per year, while visits to areas up to 20 mSv per year are unrestricted. These visits do not require permission or radiation monitoring with the only restriction being that residents may not stay overnight. Only areas with doses beyond 50 mSv per year remain off-limits to residents. In the long term, Japan's policy is to gradually prepare for a return to areas below 20 mSv per year with an overall goal to reduce additional radiation dose to 1 mSv per year.
EPA's Protective Action Guides And Planning Guidance For Radiological Incidents is open for public comment.
Researched and written
by World Nuclear News