How is emergency radiation monitoring conducted?

In the unlikely event of a nuclear accident at the nuclear power stations at Daya Bay with radiological release, radioactive materials affect us through different exposure pathways, the significance of which changes with time. For instance, direct external exposure to the radioactive plume first affects us although it is transient. On the other hand, radioactive materials enter the foodchain after several hours or perhaps several days. Only then the ingestion pathway becomes significant. Therefore, time after the nuclear accident determines the order of priority in implementing different phases, namely early, intermediate and late phases, of emergency radiation monitoring.

Early phase emergency radiation monitoring

Emergency radiation monitoring in early phase primarily serves the purpose of verifying that there is no significant radioactive plume or deposition over Hong Kong. In case there is an accident resulting in the release of radioactive materials that affect the territory, emergency radiation monitoring will rapidly determine the concentration and distribution of the radioactive materials over the territory for assessing nuclear accident consequences and considering necessary countermeasures.

As it is necessary to obtain timely information, early phase monitoring focuses on the measurement of ambient gamma dose rates, concentrations of gamma-emitting radionuclides and gross alpha/beta levels. To ensure that timely monitoring results can be obtained with minimal personnel exposure, remote sensing technology is applied as far as possible.

Emergency radiation monitoring in early phase includes:

• Full activation of instruments in the radiation monitoring network
• Conduction of emergency radiological surveys
• Measuring of environmental radiation at Ping Chau by the Automatic Gamma Spectrometry System
• Conduction of radiation monitoring at designated fire stations
• Analysis of emergency samples at King's Park Radiation Laboratory

Intermediate and late phases emergency radiation monitoring

In the intermediate and late phases of a nuclear accident, major efforts in emergency radiation monitoring concentrate on foodstuffs and drinking water. The objective is to ensure that the supplied food and water are safe for public consumption. Most of the foodstuffs in Hong Kong are imported from mainland and more than 70% of the drinking water is supplied from Guangdong. Monitoring of imported food and drinking water are conducted primarily at the boundary control points. Food imported from within 50 km of the nuclear power stations is of primary concern. Those from farms near the power stations or affected by the plume are monitored more frequently. Random screening is also applied to foodstuffs at wholesale and retail markets in Hong Kong, and drinking water in reservoirs, inlets and outlets of water treatment works, water catchment areas and consumer taps.

Below are the major monitoring systems:

• On-line Water Contamination Monitoring Systems
• Food/Water Contamination Monitoring Systems
• Livestock Contamination Monitoring Systems

The above three monitoring systems are high purity germanium based or sodium iodide based to monitor the activity concentrations of the radionuclides in foodstuffs or drinking water rapidly. Samples exceeding pre-determined screening levels will be further analysed by the Government Laboratory. All monitoring results will be transmitted to the HKO Headquarters for assessing nuclear accident consequences and considering necessary countermeasures.