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The health effects of very high doses of radiation are serious. They also are better understood than those of non-radiation hazards. Health effects of the extremely low doses of normal background radiation that we receive are so small that they can only be estimated. In fact, some studies show that low doses of radiation may be beneficial to life.
Radiation at higher levels may have two kinds of health effects: somatic and genetic. Somatic effects of radiation include a slightly increased chance of cancer and life-shortening in the person exposed. Genetic effects are those that may be passed on to the exposed person's offspring by changes in the genes.
The units used to measure radiation are the rem and the millirem (1/1000th of one rem). Individuals receive an average exposure from all sources of about 360 millirems per year. This includes natural sources (such as rocks and cosmic radiation) and man-made sources (such as X-rays). At less than 1000 millirem (or 1 rem), health effects on test animals are so small that conclusions cannot be made. Radiation doses in excess of 25,000 to 50,000 millirem (25 to 50 rem) are typically required to cause minor blood changes detectable only by laboratory examination. There are no other clinically observable effects until a dose of more than 50,000 millirems (50 rems) is received.
Radiation treatments are widely used in medicine to help cure patients with some kinds of cancer. Doses of 5,000 rems are common. Much smaller doses of radioactive materials are used as diagnostic tools. The health effects of these levels of radiation help us more than they hurt us.
From all sources, a usual person receives an average exposure to radiation of about 360 millirems per year. Most of this comes from the natural radiation in soil, water, rocks, building materials, and food. For example, potassium is a common, naturally occurring radioactive element found in many foods.
Radiation exposure from all commercial nuclear energy power plants has averaged 0.01 millirem per person annually. Those who live near a nuclear power plant receive less than 5 millirems per year. The federal limit for people who work in nuclear power plants is a maximum of 5,000 millirems per year. Utilities themselves normally have set their own limits even lower than that.
The guiding principle for releases from nuclear power plants is ALARA, As Low As Reasonably Achievable. Plant operators pay continuous, careful attention to assure themselves and the public that any radiation releases are well below the levels of significant environmental or human health effects. These levels are set by law and are based on data collected for more than 50 years. The current exposure level is 5 millirems per year at the plant boundary.
It is impossible to operate a nuclear plant with absolutely no release of radioactivity. The releases are normally not critical as far as human health is concerned, and, in fact, contain fewer radioactivities than the releases from comparable coal-fired plants.
The amount of radioactivity released by a nuclear power plant is monitored continuously to be sure it doesn't go above allowed levels. This same monitoring equipment provides exact information about any accidental release. More monitoring equipment and personnel are on hand for emergency use. Teams practice environmental/radiation monitoring several times a year in emergency drills with independent governmental agency personnel, who also practice and participate.
The greatest potential hazard from an operating nuclear power plant is from the radioactive products created in the fuel. These come from the fission process that generates the heat to make electricity. Plants are designed to keep these fission products inside the plant.
Every operating plant has plans in place to alert and advise the residents as necessary in and emergency. These are local government plans and are practiced each year with local civil authorities. These plans often have been used for emergencies that have had nothing to do with a nuclear plant. Such plans have never had to be used to evacuate the public in a nuclear plant emergency.
Реферат опубликован: 20/12/2006