What is the appropriate time for countermeasures?
The importance of individual exposure pathways is different in various phases of a nuclear accident. Since a particular countermeasure (i.e. intervention during a nuclear accident) is effective only to a certain exposure pathway, different countermeasures would be required for different phases of the nuclear accident and different exposure pathways.
| Countermeasures | Phases of a nuclear accident | ||
|---|---|---|---|
| Early | Intermediate | Late | |
| Evacuation | High priority | Low priority | - |
| Sheltering | High priority | Low priority | - |
| Control of incoming people and cargo | High priority | High priority | Low priority |
| Administration of stable iodine | High priority | Low priority | - |
| Control of foodstuffs and drinking water | Low priority | High priority | High priority |
| Exposure Pathway | Phases of a nuclear accident | Countermeasures |
|---|---|---|
| External irradiation from plume |
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| Inhalation of radioactive materials |
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| Contamination of skin and clothing |
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| External irradiation from deposited materials |
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| Inhalation of resuspended materials |
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| Ingestion of foodstuffs or drinking water |
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In Hong Kong, consideration for implementing the above countermeasures are based on a set of Generic Criteria and Operational Interventional Levels promulgated by the IAEA*.
For more details, please visit the Security Bureau's DBCP website .
Different phases of a nuclear accident
A nuclear accident is generally divided into three phases: Early, intermediate and late phases.
- Early phase
- This phase covers the period from the time when a nuclear accident at the nuclear power stations may result in the release of radioactive materials to the first few hours after the commencement of that release. The most important exposure pathways in this phase are external irradiation from plume and internal irradiation from inhalation of radioactive materials.
- Intermediate phase
- This phase covers the period from the first few hours to a few days or weeks after the radiological release. During this period, the major part of the release has taken place and radioactive materials in the air may have already deposited onto the ground. The most important exposure pathways in this phase are external irradiation from radioactive material deposited onto the ground, internal irradiation from inhalation of resuspended materials and ingestion of contaminated foodstuffs and drinking water.
- Late phase
- This phase covers the period from the latter part of the intermediate phase to the time when environmental radiation levels resume to an acceptable level. It may extend over a prolonged period of several weeks or several years. The duration of the phase varies with the amount of radioactive materials released and the extent of the affected areas. The main exposure pathways are similar to the intermediate phase.