vehicle should be directed to the survey route nearest to Daya Bay and monitor at points nearest to the estimated centre line of the plume path. A second vehicle should be directed to a route further downwind and near any major centres of population in the path of the plume. Additional vehicles should be used to define the spread of the plume in the off-axis directions.
If vehicles with beta counting and gamma spectrometry equipment are available, analysis of sample media may be carried out in the field and transmitted to the MAC. Consideration should however be given to the reduction in sensitivity which may result from the operation of gamma spectrometry equipment in an area of enhanced radiation background. It will be necessary for vehicles without counting facilities to deposit samples at suitable points for collection and delivery to the Radiation Laboratory at King's Park or other predetermined laboratories. Fire Stations would form suitable collection points, or possibly Civil Aid Services (CAS) Posts.
Suitable assistance for transport of samples should be identified. If appropriate, helicopters should be used to transport samples in the first stages of the incident where initial results are urgently required. Motorcycle delivery assistance should also be identified, perhaps provided by CAS.
Monitoring of ambient dose rate and airborne activity should continue throughout the early phase of the accident. Measurement of ground deposition by direct monitoring will be difficult while airborne radioactivity is present in any quantity. However, some sampling of vegetation should be started at this stage so that the isotopic composition of deposited activity may be determined.
The Intermediate Phase of an Emergency
During the first few hours after a warning of a release it is envisaged that the specialist staff available in the MAC would be engaged in assessing data transmitted from the fixed monitoring stations and from the mobile survey vehicles. After the early results have been collated and an assessment made of the need to implement early countermeasures, more staff should become available to supplement the monitoring teams by collecting environmental samples.
Sampling teams will require a greater degree of specialist knowledge than monitoring teams, and should where possible be drawn from staff involved in the routine environmental sampling programme. The teams will be required to monitor foodstuffs, and to take samples of vegetation, milk, crops, surface and drinking water, and soil samples. In addition they will change filters on high volume air-samplers at fixed monitoring stations, and change some environmental radiation detectors as necessary at fixed locations near centres of population. All samples will be returned to the Radiation Laboratory at King's Park, or other predetermined laboratories.
Surveys of ambient dose rate will continue in order to build up a picture of the spread of radioactive contamination. In this context the use of helicopters to carry out airborne surveys may be useful. It has been shown (ref 21) that a helicopter flying at 50- 100 ft can detect levels below 13kBqm2 I-131 (the derived emergency reference level for introducing a milk ban given in reference 38).
In monitoring the food-chain it is important that surveys initially concentrate on the material which will reach the consumer first. This will include fresh produce such as vegetables, fruit, etc., already in shops and markets which could have been exposed to the passage of the plume, supplies of milk, and drinking water. The interdiction on crops in any area can be based on the results of general surveys of deposited activity, until data from detailed sampling and testing becomes available. Milk samples should be obtained from each farm in the affected area. Water samples should be obtained from the water running off the catchment area into the reservoir, from the reservoir (at various depths), and from the treatment plants (both before and after treatment).
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