epr-method (2003) - IAEA Publications - International Atomic Energy ...

(2) At these radial distances there is a factor of approximately ten reduction in
concentration (and thus risk) from a release compared to the concentration at the PAZ
boundary.
(3) This distance provides a substantial base for expansion of response efforts.
(4) 25 km is assumed to be the practical limit for the radial distance within which to
conduct monitoring and implement appropriate urgent protective actions within a few
hours or days. Attempting to conduct initial monitoring to a larger radius may reduce
the effectiveness of the protective actions for the people near the site, who are at the
greatest risk.
(5) For average meteorological (dilution) conditions, beyond this radius, for most
postulated severe emergencies, the total effective dose for an individual would not
exceed the urgent protective action GILs for evacuation.
Threat category II facilities
Atmospheric release
(1) For average meteorological (dilution) conditions, beyond the UPZ radius, only the most
severe postulated emergencies would result in a total effective dose for an individual
exceeding the urgent protective action GILs for evacuation.
(2) Preparations within this radius provide a substantial base for implementation of
effective urgent protective measures beyond it, if needed.
(3) 0.5 km was selected as the smallest radius considering of building wake effects.
Fissionable mass (criticality)
(1) The radiological risk from a criticality is dominated by the external dose from gamma
and neutron radiation.
(2) Beyond this radius, most accidental criticalities would not result in a total effective dose
for an individual exceeding the urgent protective action GILs for evacuation.
(3) The off-site doses from past criticality accidents have not warranted urgent protective
measures beyond 0.5-1 km.
Food restriction planning radius (threat category V distance)
This is the area where preparations for effective implementation of protective actions to
reduce the risk of stochastic health effects from the ingestion of locally grown food should be
developed in advance. In general, protective actions such as relocation, food restrictions and
agricultural countermeasures will be based on environmental monitoring and food sampling.
The suggested radii were based on expert judgment considering the following:
(1) Detectable excess stochastic effects (cancers) are very unlikely beyond this distance.
(2) Detailed planning within this distance provides a substantial basis for expansion of
response efforts.
(3) Food restrictions were warranted to about 300 km following the Chernobyl accident in order
to prevent detectable excess thyroid cancers among children.
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