Bulletin Number Two 1984

of interferences. K. L iu : There are different states of air pollutants: gaseous state, such as carbon dioxide; solid state, such as most particulates; and a combination of the two, such as the vaporized organic or inorganic matter coated on the surface of the particulates. These aerosols, in different states and of different sizes, are suspended in the air; and the smaller the particle size and the further their dispersal, the greater their chance of being inhaled into the respiratory system and thus the greater their hazardous effects on the alveolar region of the lung. In 1983 ， respiratory diseases were one of the three major groups of diseases in Hong Kong. Since the pollutants are of different states, the methodologies and instrumentation for measurement are different. Basically they measure the physical characteristics (e .g. mass, size, shape, number and electrical charges) and the chemical compositions (e.g. organic or inorganic contents). A t Daya Bay a nuclear pow er p la n t is to be constructed. What possible im p act w ill i t have on the environm ent o f H ong Kong? L.S. Chuang: With nearly 3000 civilian reaction years of operation experience and with nearly 10% of total world electricity generation coming from nuclear energy, safe operation of nuclear power plants is con sidered by many to be possible on the basis of existing regulations and design principles. Nevertheless, I should like to provide the following information to help the general public to be on their guard against mal-operation of a nuclear power plant. The advantages of a nuclear power plant as a source of power must be seen in the context of: (i) The protection of the operators andmaintainers of the power plant; (ii) The safe treatment and disposal or storage of the enormous quantities of radioactivity pro duced as a result of nuclear power generation; (iii) Achieving an acceptably low risk of injury to the public in the event of a reactor accident. These problems can be solved to a reasonably satisfactory extent i f the laws and regulations for safe construction and operation of nuclear power plants are followed rigorously. It is generally agreed, so far, that the nuclear energy industry has an excellent safety record. To control the amounts of radiation received by the public, the International Commission on Radiological Protection (ICRP) was established in 1928 and has been the one internationally recognized body responsible for recommending values of maximum permissible exposure (MPE) to ionizing radiation. Based on the recommendations of ICRP the International Atomic Energy Agency (IAEA) has established, and continuously revises, a code of internationally agreed safety standards for radiation protection. In 1958, the ICRP gave the following definition of MPD (Maximum Permissible Dose): 'The permissible dose for an individual is that dose, accumulated over a long period of time or resulting from a single exposure, which in the light of present knowledge carries a negligible probability of severe somatic or genetic injuries'; the Maximum Permissible Occupational Dose (MPOD) since 1956 is 5 rem/year ， or approximately 0.1 rem/week, reduced by a factor of 10 for members of the public. The increases in radiation levels in the surround ing environment, including the territory of Hong Kong, during the operation of the power plant must be measured continuously and the result be made known to the public. Furthermore, the public should be advised of the degree of health hazards and the protective measures to be taken in case of abnormal release of radioactive materials from the plant. What is the nature of radiation hazards involved in running a nuclear power plant? In general, i f a nuclear power plant is operating properly, radiation hazard is slight. During shut-down periods, a great variety of non-routine jobs may be undertaken, some of them on highly radioactive systems. It is during such periods that exposure of personnel to radiation and radioactive contamination must be carefully controlled. A serious fault or mal-operation of the plant could cause considerable damage to the plant and give rise to dangerously high levels of radiation or radioactive contamination. If the hazards is confined to the plant site it is often called a site emergency but i f it extends off-site it may become apublic emergency.