9
COUNTERMEASURES
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Following any accidental release of radioactivity the radiation dose to the affected population, and hence any detrimental health effects, may be reduced by the use of countermeasures.
In general countermeasures may be divided into two groups: countermeasures to reduce the dose due to exposure from the plume, and countermeasures to reduce the dose due to ingestion of foodstuffs, etc., contaminated by the plume. These two groups will be referred to as the 'plume countermeasures' and the ‘ingestion countermeasures' respectively.
Plume countermeasures will in general need only be considered in an area relatively close to the reactor site. The countermeasures which may be considered in this area will include sheltering, issue of stable iodine tablets, evacuation, control of access to and egress from the affected area, etc.
The ingestion countermeasures generally will need to be applied over a larger area and out to distances further from the reactor than the plume countermeasures. Ingestion countermeasures which will need to be considered include interdiction of contaminated foodstuffs, especial milk. Serious contamination of drinking water is unlikely to be a major problem, however there are a number of methods for reducing the contamination levels in water supplies and these
may need to be considered.
9.1 Emergency Planning Zones
It can be useful when planning contingency arrangements to use the concept of emergency planning zones. These are areas around the reactor in which consideration has been given to how the relevant countermeasures would be applied. The area in which consideration has been given to the application of plume countermeasures will be referred to as the emergency planning zone (plume) and similarly the area in which consideration has been given to the application of the ingestion countermeasures will be referred to as the emergency planning zone (ingestion).
The size of the zones will depend upon the potential size of the release of radioactivity, the potential weather, the local geography, etc. There is however a reasonable consensus of international opinion about the sizes of these zones. The emergency planning zone (plume) is typically out to 5-20 km from the reactor. The emergency planning zone (ingestion) is typically out to 20-100 km. (See Table 5.1). Clearly a release of radioactivity will only significantly affect the downwind sector, and for planning purposes a 30° sector is usually chosen.
Very roughly Hong Kong falls within 60° a sector from the Daya Bay reactor, from 25 km to 85 km. As such it is unlikely that the majority of Hong Kong would be significantly affected following any accidental release from the Daya Bay plant. The actual areas affected would depend upon the wind direction, rainfall pattern, etc. The wind roses for Daya Bay and Waglan Island are shown in Figure 9.1.
It is highly improbable that any plume countermeasures would be required in Hong Kong following any accident at the Daya Bay plant, however for completeness such a scenario will be discussed later.
9.2 Timescales
As discussed in Chapter 4 deposition of radioactive material from the plume onto crops and grazing pasture can lead to radioactivity entering the food chain. The purpose of ingestion countermeasures is to prevent significantly contaminated foodstuffs or water being consumed by man.
Exposure from the plume is likely to occur over a relatively short period, perhaps a few hours. Exposure via the ingestion pathway is a much slower process and if no countermeasures were introduced exposure would occur over a period of days, weeks or months. There is therefore not quite the same urgency to introduce ingestion
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