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Mayak Environmental pollutionThe Techa RiverIt is estimated that about 76 million cubic metres of radioactive waste with total radioactivity of 100 Peta Bq was discharged into the open hydrographic drainage system connected to the Techa River in the period up to 1951. Since then the waste has been stored in an isolated reservoir on the plant's site at Karachai.
It is difficult to assess the severity of exposure to radiation experienced by the local population due to the high degree of secrecy surrounding the plant at the time. Epidemiological and medical research started later when recording began of the long-term affects of high level exposures to radiation on 124,000 residents. Around 7,500 people living alongside the Techa River received significant radiation doses; those subsequently moved from 20 locations received doses of 0.03-1 Зв. The highest doses (up to 1.7 Gy) were received by the residents of the riverside village Metlino. According to official data there are 66 cases of chronic radiation sickness among the village's residents. The radioactive waste has accumulated on the bottom of the river. The chain of polluted industrial reservoirs known as the Techen cascades occupies an area of about 70 square km and has a volume of about 380 million cubic meters. Currently 90Sr and 137Cs are the main pollutants, while specific water activity in the basins is about 0.1-10 kBq/liter. The levels of silt pollution differ greatly from 1 up to 107 kBq/kilo. The Techa's floodplain areas (Asanovsk swamps), where silt pollution exceeds the allowable level, are ecologically dangerous. The Karachai LakeThe polluted Karachai Lake, located on the plant's site, covers about an area of about a quarter of a square kilometre and has a volume of about 400,000 cubic metres. Currently the total radiation is estimated at 4.4 Ebq, with specific water activity of 90Sr и 137Cs being 0.06 and 0,4 GBq/liter, and soil 10 and 50 GBq/litre. The water lens of Karachai Lake rests on a layer of clay, which significantly isolates the radionuclides, preventing them from being washed away. Nevertheless, the polluted area has gradually spread outwards. There is an estimated amount of underground water covering 30 square km with a volume of up to 4 million cubic metres. This has a high content of cesium and strontium. In 1967, during a summer drought, the water level in the lake dropped, revealing a strip of sediment at the bottom. About 2,700 square km of surrounding land were subsequently polluted through wind dispersal of the sediment. Resulting radiation levels were not high, varying from 13 mGy (suffered by 4,800 residents nearby) up to 7 mGy (affecting residents furthest away). Although there was no affect on human health, measures had to be taken to prevent a similar incident happening again. Concrete panels shaped like upside-down glasses have been placed on the bottom of the lake to protect the lake's surface. From above the blocks have been covered with rocks. Currently about 70% of the reservoir's surface has been covered. A chain of drilling holes has been made around Karachai to enable continuous monitoring of soil and subsoil water pollution at various depths and distances. The 1957 explosionFollowing the explosion at the plant in 1957, about 90 per cent of the radioactive material fell on the plant itself. Some of the radioactive substances exploded out into the atmosphere, about 70 PBq, with short-life cerium-144 and zirconium-95 forming the main part of the discharge (over 90% of the total volume). The cloud, which had completely settled within 11 hours, left a trace 300 km long and between 30 and 50 km wide. This has been named the Eastern Ural Radioactive Trace (VURS). As a result of the accident about 23,000 sq km was exposed to radiation, including 217 homes. The area restricted by the insulation line has a radiation pollution level of 0.1 Curie/km2. The territory with the most significant pollution (more than 10 Curie/km2) covers about 0.4 thousand sq km. About 1,200 people were evacuated, mainly during the first day of the accident. They received radiation of 0. 5 Gy. A further, 11,000 people were moved later. They received average doses of 0.2 Gy. The Russian Academy of Medical Science and Institute of Biophysics reported that sickness among the population has been avoided due to the efficiency of the measures undertaken. The decision to locate the plant downwind from the main settlement also helped to reduce the impact of the explosion. Radioactivity levels have now decreased 15 times since the half-life period is less than a year and most of the area was brought back within safety standards by 1982. Almost all of the land which received initial pollution of up to 4 Curie/km2 is currently being used for agriculture. Long term ecological problems associated with VURS have been caused largely by strontium-90 together with its daughter yttrium, which formed 5.4% of the initial discharge. Research into radioactive ecology and biology is now being carried out in the remaining area, covering some 170 sq km, known as the Eastern Uralian Reserve. One of the world's largest centres of radiological research, a branch of the Biophysics Institute of the Russian Academy of Science (FIB-1), was established in Ozerskin 1953. Research has shown that the greatest impact on human health was in the early years of the plant's operation. This includes radiation sickness, high cancer rates, and thyroid gland disease in children. The current medical and ecological situation in Ozersk is not of major concern. "If one compares our Ozersk children with, let's say, Moscow kids, you will see that ours are much healthier in every way," says Sergei Romanov, FIB-1 director. The Yekaterinburg Institute of Industrial Ecology carried out an independent survey in the areas surrounding the trace made by the 1957 accident, and concluded that the radiation factor ranks 10th or even 12th behind other man-made factors affecting human health. | |
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