Annual Report 2001 (Summary)
The Observatory embarked upon a comprehensive environmental radiation monitoring programme (ERMP) in 1987, the objective of which was to monitor the effects on Hong Kong's radiation level from the construction and operation of the Guangdong Nuclear Power Station (GNPS) at Daya Bay in Guangdong. In late 1992, the Observatory published a report on the background results for the period from 1987 to 1991, prior to when the GNPS began phasing in its operation. Since 1992, the Observatory publishes its results and findings in annual reports as part of the ongoing operation of the ERMP.
Year 2001 saw the fifteenth year of operation of the ERMP. The network of ten fixed monitoring stations continued to monitor the ambient gamma radiation level in Hong Kong. The annual level ranged from 0.086 to 0.139 μGyh-1 and was within normal background fluctuation. So far, the measurements showed temporal variations that can be attributable to variations in the meteorological conditions and physical environment adjacent to the station. The largest variation in the ambient gamma radiation level since the operation of the network occurred on 23 June 2001. Under the combined effects of subsidence air ahead of Typhoon Chebi and an outer rainband, the ambient gamma radiation level at Ping Chau increased from its background level of 0.084 μGyh-1 to 0.233 μGyh-1 over a couple of hours, i.e. a rise of 177%. Owing to the renovation and rebuilding work in the vicinity of the Tai Mei Tuk station, the ambient gamma radiation level at the station increased by around 5% during December 2001. The increase was due to the radiation emanated from the natural radioactive substances in the building materials used in the renovation work and of the rebuilt building.
Radiological survey, which consists of the aerial survey and the mobile survey, was conducted in 2001. The aerial survey aims at detecting radiation level at different altitudes using the Aerial Monitoring System (AMS). The mobile survey makes use of the Mobile Radiation Monitoring Station (MRMS) to carry out radiological measurement and sample collection in different parts of the territory. Background measurements over Sai Kung and the Po Toi Islands using AMS were completed. No artificial radionuclides were detected so far. The results of the mobile survey showed that the terrestrial environmental gamma dose rate in open field ranged from 0.040 to 0.139 μGyh-1 with an average of 0.088 μGyh-1, comparing very well with the data obtained from the monitoring stations. The dose rate in built-up areas ranged from 0.120 to 0.224 μGyh-1 with an average of 0.175 μGyh-1. Detailed mobile surveys were conducted at the designated emergency survey sites in the Daya Bay Contingency Plan. So far, no artificial radionuclides had been detected.
The Observatory collected 400 environmental and foodstuff samples in 2001. Some one thousand alpha, beta and gamma measurements were made and specific activity concentrations of all artificial radionuclides detected were within the corresponding background values. Large variation in the specific activity of the naturally occurring radionuclide potassium-40 was measured in several types of aquatic samples. This could be related to the salinity of seawater contained in the samples.