EMERGENCY PLANNING ZONES FOR RADIATION EMERGENCIES – HOW THE ZONES ARE CALCULATED.
This is an explanation of the technical methods used to determine an Emergency Planning Zone around nuclear installations. It is based on notes made at a presentation to NAG by Nigel Holloway, a former AWE employee, in September 2001.
Only reasonably foreseeable accidents are considered and acts of war are not assessed.
The aim is to reduce the exposure of the public by warning them to take shelter or to temporarily evacuate the area in the event of possible risk.An aerosol radiation plume creates the highest risk that people might inhale plutonium. Heavier particles that fall to earth do not constitute an emergency as they can be dealt with more slowly. In average wind and weather conditions, a dangerous aerosol will travel 1Km in 3 minutes. Little warning or remedial action can be taken unless the accident develops slowly, as in a fire. As it spreads, the aerosol will gradually be diluted, and the limit of the danger zone at Aldermaston is set at 3Km and at Burghfield at 1.5Km. The HSE say that these limits will not change under REPPIR (the Radiological Emergency Preparedness & Public Information Regulations) that came into force on 20th September 2001.Mathematical models are used to calculate the risk to an exposed person and there are some down to earth tips on preventing plutonium from entering the lungs: breathe through 15 layers of shirt material, or 6 layers if it is wet. Having a shower also offers protection, as the aerosol will be taken down in the water.
For those wanting the technical calculations a 6-page paper is available from NAG.
NAG SecretariatNovember 6th 2006