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АРИДНЫЕ ЭКОСИСТЕМЫ, 2005, том 11, №26-27
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ПРИРОДНЫЕ И СОЦИАЛЬНЫЕ АСПЕКТЫ РАДИО -ЭКОЛОГИЧЕСКОЙ СИТУАЦИИ В КАЗАХСТАНЕ
© 2005 г. 1 А.Н. Ермилов,2 Е.В. Ермилова
1Институт Ядерной Физики НЯЦ РК 2 Казахский национальный университет Аль-Фараби, 480012, Алматы, ул. Карассой Батыра 95а, Казахстан
В статье представлен обзор сложившейся в Казахстане радиоэкологической ситуации, а также описание ядерных и радиационных факторов, имеющих влияние на окружающую среду, названы природные и техногенные факторы, определяющие уровень радионуклидного загрязнения окружающей среды, и обсуждается возрастающая роль радиоактивности как фактора окружающей среды человека. Ни в одной другой стране мира вопросы, связанные с радиоэкологией не приобрели такой остроты, как это имеет место в Казахстане. Масштабы радиоэкологических проблем и их разнообразие выводят их в один ряд с первостепенными экологическими проблемами региона такими как вопросы воды и хозяйственной деятельности человека. Кратко обсуждаются некоторые социальные вопросы и проблемы жизнедеятельности человека на территориях со сложной радиационной обстановкой, делается утверждение о том, что человечеству придется искать пути выживания в условиях повышенного радиационного фона. .
ENVIRONMENTAL AND HUMAN DIMENSIONS OF RADIO-ECOLOGICAL
SITUATION IN KAZAKHSTAN
© 2005. lYermilov A.N., 2Yermilova Ye.V.
1 Institute of Nuclear Physics of National Nuclear Center, Kazakhstan 2 International Academy of Business, Almaty, Kazakhstan
Introduction
Kazakhstan is a land of 5 nuclear test sites where about 500 nuclear explosions were performed by USSR; this land is very rich in uranium ore, has a well-developed uranium industry, and plans to become one of the world's leaders in uranium production. Famous for its largest Semipalatinsk Nuclear Test Site (SNTS in operation from 1949 to 1989) and a launching site of Soviet and, currently, Russian space programs (including launching of the first astronaut Yu. Gagarin), this land now suffers from a terrible nuclear heritage. It now faces the problem of dealing with hundreds of thousands tons of radioactive waste and assurance of radio-ecological safety at operating facilities.
Kazakhstan is one of the rapidly developing countries in the region and possesses up to 15-20% of the world's stock of uranium ore [1] and commercially produces almost all chemical elements. The country positions itself as an important uranium producer; it is developing its nuclear science that currently operates 4 research nuclear reactors and other facilities including accelerators, cyclotrons, and modern laboratories. It constructs modern laboratory complex in Gumilev Eurasia National University with the first in Central Asia powerful accelerator of heavy ions; there are plans to construct a new nuclear power plant (NPP) near Almaty. At the same time, the country earns experience with monitoring of the consequences from so-called peaceful nuclear explosions and assures radiation safety at oil extraction, keeps at high level commercial production of uranium; together with IAEA and the USA it runs a decommissioning program of its fast neutron nuclear reactor, BN-350.
Below there is a list of factors that contribute to present radiation situation in the country:
Numerous tests of nuclear weapon and nuclear explosions performed in different places for economic purposes such as "Azgir", "LIRA" and other facilities; 456 nuclear explosions have been performed at former Semipalatinsk Nuclear Test Site; there are total 5 nuclear test sites in Kazakhstan;
for instance, surface activity of Cesium-137 in the central part of Eastern-Kazakhstan Oblast ranges from 65 to 100 mCi/km2
- global atmospheric radioactive fall-outs due to surface and air nuclear tests in other countries
- high level of natural background radiation, the rate of which, for instance, in Almaty is three times higher than in New York City or Moscow; this pattern is evident in regions rich with uranium and thorium/rare-earth metal ore.
- high content of radio-nuclides in natural waters of "uranium ore provinces"
- activity of uranium mining and uranium production industry and related to uranium production geological explorations
- activity of non-uranium mining and production industry (oil, coal) and accompanying processing enterprises that mine and use raw materials with increased concentrations of natural radio-nuclides
- activity of nuclear facilities - 4 operating nuclear reactors and one NPP at decommissioning since 1999
- other commercial and civil enterprises (industry, science, medicine) that utilize radioactive materials; there are more than 800 enterprises in Kazakhstan that use about 80,000 sources of ionizing radiation with total activity more than 250,000 Curies.
- various radioactive waste; a hundred burying places dispose 225 million tons of low-level radioactive waste with total activity more than 230,000 Curie.
About 13% (350,000 km2) of Kazakhstani territory is subjected to influence of known radiation hazards this area covers territory 19 times exceeding the territory of SNTS. To compare the scale, this area is the size of Germany. Within this area, there are more than 1 million people living with increased exposure to radionuclides.
Presented above are academic facts that illustrate the importance of the radio-ecological problems in the country, but they cannot describe their impact on the social and political life of the country. Within academic consideration one should keep in mind other related facts about Kazakhstan that, to a certain extent, may add to understanding of the complex situation in the country and also the role of international community/organizations in it:
Actual, but not just manifested dedication of Kazakhstan to the principles of open democratic development in the field of non-proliferation, peaceful utilization of nuclear technologies, international cooperation in solving global and regional ecological problems. Those who study political situation in Central Asia describe quite specific from western point of view "face of democracy" in the region. It should be stressed that progress in nuclear-related issues in Kazakhstan is coherent with internationally recognized understanding of activities in this field.
Kazakhstan is the only state in the world's history that, having really possessed nuclear weapon for a very short period of time (1410 nuclear warheads), voluntarily refused possession, keeping at its territory and development of this weapon. (Actually, Ukraine returned Soviet nuclear weapons back to Russia as well, but there was a great deal of paltry bargains.) This fact is one of the few that create the positive international image of our country. It becomes of even greater value when the geopolitical situation in Central Asia is taken into account.
All nuclear related facilities and sites are open to international inspections and assure non-proliferation measures. Kazakhstan is a party to START-1, the Nuclear Non-Proliferation Treaty (NPT), and the Comprehensive Test Ban Treaty (CTBT).
Kazakhstan still keeps its positions in advanced nuclear-related and radio-ecological research; in this field it works in close cooperation with the USA, EU, Japan, Russia, and other countries.
Kazakhstan is one of the leading producers of uranium fuel in the world.
When the USSR collapsed, Kazakhstan was left alone to solve huge radio-ecological problems at its territory as a consequence of terrible Soviet heritage.
Kazakhstan is receiving pioneering experience solving radio-ecological problems during decommissioning of Aktau reactor BN-350.
Overview of factors contributing to radio-ecological situation in Kazakhstan
In investigations of radio-ecological situation and development of measures for lowering radiation risks to people and land subjected to radiation hazards, one should first of all identify radiation sources. All radionuclides are traditionally classified as natural and artificial ones. Opposite to natural radionuclides that normally exist in environment, artificial ones are those, generated as result of human activity in nuclear explosions or in nuclear reactors.
In international practice when environmental impact assessment includes nuclear component1 due to, for instance, activity of uranium mining industry, an accident at a nuclear facility or in a place of radioactive waste disposal, there is, as a rule, the only source of contamination or potential radiation hazard. From this point of view, Kazakhstan becomes a very unique example because in some territories several mutually independent factors are nuclear contributors to the general radiation situation. This situation becomes even more dramatic when one realizes that some of the contributing factors are poorly studied and radiation hazards from other sources have sometimes been underestimated.
A good example is Western Kazakhstan oblast where several radiation hazardous objects of different type contribute simultaneously into the radiation situation in the region. Radiation situation in Aktau city of Mangystau oblast in Western Kazakhstan has been affected by the Mangyshlak Atomic Energy Combine with reactor facilities BN-350, the sites of underground nuclear explosions at Plato Ustiurt, extracting and processing uranium facilities and a large number of operating their oil extracting companies.
Reactor Facilities BN-350
Construction of one of the most powerful breeding reactors in the world BN-350 was started in 1964 in Aktau and in 1973 it was commissioned. For more than 25 years till 1998 it was a reliable source of heat and electricity for the entire Mangyshlak Peninsula:
1) Thermal power - 1000 MW, 2) Electric power - 350 MW, 3) Up to 120,000 tons of desalinated water per day, 4) Buildup of tons of weapon-grade plutonium, 5) Primary loop coolant - liquid sodium, and 6) Fuel enrichment - large amounts.
In April 1999 according to a governmental decree, the Aktau reactor was stopped and a decision was made to transfer it into long-term safe store for 50 years followed by final dismantling. Since that time huge scope of decommissioning works are in progress with financial and technical support provided by the USA and International Atomic Energy Agency (IAEA).
Decommissioning of such facilities has no analogy in the world's history. Coolant of the primary loop, tons of liquid sodium that is a very active chemical even at room temperature, was kept at temperature 400°C and during operation became highly radioactive. Decommissioning implied multiple operations with nuclear materials including processing, packing, transportation to thousands kilometers, handling-over manipulations, long-term storage (ageing) in water, conversion of radioactive waste into stable form for final disposal, etc. Nuclear materials in this case are highly enriched nuclear fuel, spent nuclear fuel, radioactive sodium from the primary loop, other various-type radioactive waste. Each step of decommissioning program brings up a challenge to scientists, engineers, specialists from various fields to assure physical protection and nuclear non-proliferation measures (first of all, for plutonium-containing elements), radiation and operational safety, lowest risks for personnel, population and the environment.
Decommissioning of a nuclear reactor is, according to international experience, an extremely expensive project that takes many years of realization. In 2002 decommissioning plan presented by
1 It should be noted here that everywhere in the world environmental impact assessment is performed as a complex investigation that evaluates relative contributions to environmental conditions from different factors. Such investigations may need expertise of specialists in various fields ranging from chemistry and biology to sociology and environmental law. But when there is a nuclear component among the contributing factors, an entirely different team of specialists is involved and very different organizations became in charge of the investigations. Nuclear-related issues, being sensitive, are always considered in a very different manner.
Kazakhstan passed preliminary expert assessment in IAEA, upon correction this plan is to be presented to independent expertise and, after approval in Kazakhstan, will be presented to country donors for consideration of possibilities for funding.
Naturally, this project intensified through radio-ecological investigations and the monitoring of radiation situation at the site and their adjacent territories. Conclusions made by specialists from the Institute of Nuclear Physics of National Nuclear Center of the Republic of Kazakhstan upon many years of studies say that in all environmental samples taken at territory of sanitary-protection zone and monitoring zone of BN-350 reactor content of artificial radionuclides corresponds to average for Western Kazakhstan levels of global fall-outs. Available retrospective data on releases also evidence that during the whole operation period of the reactor plant there was no exceeding in acceptable annual environmental release of radioactive substances.
Therefore, contribution of BN-350 into radio-ecological situation within the sanitary-protection and monitoring zones can be detected employing highly-sensitive methods and this contribution is vanishingly small and does not result in quality change of the environment. At those territories there were revealed no single case of exceeding regulatory allowable contamination of environment with artificial radionuclides [3].
Underground nuclear explosions
In 1983-1984 in the Northern part of Karachaganak oil and gas field at Plato Ustiurt were performed six so-called peaceful nuclear explosions to construct underground cavities for storage of gas condensate. These cavities known as LIRA facilities are of about 50,000 m3 each and lie 800 - 900 m below the surface. The explosions did not result in release of any significant amount of radioactivity and the cavities, except one of them is filled in with groundwater, were used for gas storage at Soviet times. In 1990s new oil operators in independent Kazakhstan refused utilization of these cavities in their technological process.
Since 1998 INP NNC RK was in charge of scientific investigations and radiation safety assurance at LIRA facilities. As a result it was revealed, that at near-mouth sites of the explosion wells there are local areas of soil contaminated with artificial radionuclides 90Sr and 137Cs. According to walk y-surveillance, there is insignificant area up to 50 m2 with registered exposition dose rate (EDR) for y-radiation of about 25-30 ^R/h at background values for that region 8-10 ^R/h. Since there are no inhabited places in the vicinity and the rate of radioactive contamination is low (within allowable limits), these sites do not impose considerable radiation hazard on the region.
There are still concerns about potential hazard from LIRA facilities. If radionuclides formed at nuclear explosions came out to the surface and distributed uniformly over it, soil at the territory exceeding 500 km2 would be considered as radioactive waste. So, it is necessary to prevent proliferation of radionuclides from the cavities to human environment through wells, technological lines or migration in underground water.
Based on obtained results, specialists made the conclusion that current radio-ecological situation at LIRA facilities is stable and safe. No radiation anomaly of exceeding radiation background was revealed. There has been established a well-developed radio-ecological monitoring system that enables registration of unfavorable trends in radiation situation at the site. Therefore, at present time LIRA facilities are not a source of radioactive contamination and do not impact radiation situation in the region [4].
Natural radionuclides are of much greater concern, since their main sources are tailings from oil extraction, mining and uranium industries.
Oil extraction facilities
In recent years, it has become increasingly evident that the subject of radiological protection of the environment including that of wild plants and animals from radiation exposure, as opposed to the more frequently accepted interpretation in terms of the possible resultant impacts on humans arising from contamination by radionuclides, has an increased profile on the scientific/political agenda.
Currently, radioactive contamination with natural radionuclides at industrial sites of oil-and-gas fields is well known among specialists, but still an unresolved problem in many countries.
Oil and bearing strata contain radionuclides of radioactive series U-238 and Th-232. Upon radioactive decay and leaching processes there is a continuous formation of radium isotopes in oil. Content of radium in water-free oil condensate is at levels of about 280 Bq/m3. In Karachaganak oil-and-gas field specific content of natural radionuclides (226Ra) in extracted condensate lies within the range 0.4 Bq/kg (annual average content) to 3-7 Bq/kg (i.e. up to 510 Bq/m3).
Extraction and transportation of oil condensate is accompanied with carrying out to day surface of considerable amounts of materials with increased content of natural radionuclides. Amounts of radioactive materials accumulated at the fields are described in terms of thousands tons, activity of radionuclides delivered to human environment - in dozens of Curie; and up to 70% of radioactivity is accumulated in pressure-compressor pipes and other metal equipment. Such amounts of radioactive materials increase natural background for orders of magnitude at total areas of several hectares and must be taken into account due to the hazard imposed on personnel and population [5].
Contaminated metal discard, particularly pipelines, is of highest hazard due to their possible unauthorized utilization by local population for water supply and construction. Such metal discard at oil extraction fields is incompletely accounted for, rates of their contamination and related factors of radioactive hazard such as mass amount and activity have not been determined for most cases.
In the region, where oil-extracting companies operate were 231 registered radioactive anomalies [6], 192 of which were classified as man-caused technological radioactive contamination sites. Actual source of radioactive contamination are stratal water in the zone of water-oil interface. Stratal waters at oil fields contain highest concentrations of radium (10-8-10-11 %) compared to all other known stratum waters, except waters from uranium fields.
Anomalous spots with masout soil cover areas of up to tens thousands square meters with EDR of 30 ^ 100 ^R/h at natural background 8-11 ^R/h. Such soil is brown and usually covered with solid oil skin. At places of extensive or multiple releases, average level of radioactive contamination comprises for y-radiation 250-600 ^R/h at territories of tens or hundreds of square meters; local maximal readings may be as high as 1000 - 2800 ^R/h. Internal surfaces of equipment and tank bottoms keep sediment oil-slime and salts with high radionuclide content. Radioactivity of metal discard comprises on external surfaces 400 - 10,000 ^R/h. At all oil extraction sites, mainly at middle- and final stages of exploitation, technological equipment and pipelines are contaminated with natural radionuclides.
Spent uranium mines
In 2002 specialists from INP performed over-all radio-ecological investigation of two spent uranium mines 20 km away from Aktau [6].
Not all the tailings are covered what stipulates their negative impact on environment with direct radiation impact from gamma-radiation, radon emanation and aerosol-dust proliferation, transport of uranium and radium with periodical water flows into soil water horizons and local hydrological system.
Keeping in mind years of dramatic political transformations in the country and years of economical chaos, one should note that along with natural factors contributing to radioactive contamination of environment there is another, equally hazardous influence. This is radioactive contamination due to uncontrolled utilization of mining tailings in local building or road construction that takes place in inhabited localities adjacent to abandoned sites of geological prospecting and spent uranium mines.
The main contaminating factor is radionuclide-containing dust proliferation. The intensity of this process to a certain degree also depends on weather-climate conditions. One can only reliably determine contribution from this factor only when monitored investigation is undertaken.
Tailing Pool "Koshkar-Ata"
Liquid radioactive wastes from Chemical Hydrometallurgical Plant during its operation were discharged into open off-channel reservoir. The tailing pool Koshkar-Ata was made in natural closed hollow and covers 130 square kilometers, 7-8 kilometers from the Caspian Sea coast and 5 km north of the town of Aktay. Amount of accumulated solid waste is about 104.8 mln. tons including about 51.8 mln. tons of radioactive waste (RW) with total activity 41598.5x1010 Bq [7,8]. During operation of this tailing pool in 1964-1992 amount of waste discharge exceeds considerably the evaporative capacity what resulted in continuous increase of water level and area of tailing pool mirror.
Continuous delivery of tailing material from one source caused formation in 1986-1967 of above-water solid sediment in the southern part of the tailing pool, a so-called "beach".
In 2003 specialists from INP performed pilot monitoring of dusting from radioactive and toxic waste storage Koshkar-Ata [11]. Main dose-forming radionuclides in the waste stored there are 238U, 230Th, 226Ra and 222Rn; concentration of 226Ra changes from background values of 15-20 Bq/kg to 700-800 Bq/kg. There were revealed quite high concentrations of lead isotopes 210Pb and 212Pb.
Man-caused ecological hazard from the tailing pool is stipulated by two main factors: a) air pollution and soil contamination with radionuclides and heavy metals in adjacent to the tailing territories due to wind erosion from naked bottom sediments and, b) contamination of underground water and possible proliferation of hazardous substances in dense saline solutions into the Caspian Sea.
Due to continuous decrease in water phase level of the tailing pool, area of exposed bottom sediments, a source of radioactive and toxic dust, increases. Water mirror covers 42.5 km2 and shore exposed zone is as large as 34.5 km2. A near-surface disposal of RW is located in the mouth part of the tailing pool. Its detailed gamma-surveillance (covered 8,700 m2) revealed very high radiation levels.
Waste accumulated in the tailing pool substantially influences soil and vegetation in adjacent territories. Immediately at the site, its impact on the physical, chemical and biological parameters is maximal; waste completely covers the surface, makes soil more dense, with higher content of water-soluble salts and less microbial mass in it. Within the site, vegetation is completely vanishing. At the tailing pool, total area subjected to such catastrophic change comprises about 70 km2. Chemical and biological parameters of soils at significant distance from the pool have also worsened; this has been accompanied by vegetation degradation.
When estimated possible technologies for the rehabilitation of this exposed shore zone at Koshkar-Ata, the cost factor becomes crucial since cost of any traditional rehabilitation actions in such a vast area (11 km2) rises up to millions of US dollars what is not affordable for Kazakhstan. Traditional technologies are technologies that imply isolation of shallow lands with some available and cheap local material such as, for instance, clay or sand, or those are technologies based on processing of soils in order to increase effective size of soil grains (such as processing with polymers). Specialists also look for other cheaper ways to solve the problem [11].
General considerations on example of Mangystau oblast
Based on comparison of existing radio-ecological hazard sources and taking into account presented above description one can get to the following main conclusions:
radio-ecological problems at BN-350 facilities and sites of nuclear explosions are not of the primary concern and they even attract unreasonably much attention;
main accent is to be done on investigation of the radio-ecological problems in the regions where transport and redistribution of natural radionuclides takes place due to commercial activity;
natural radionuclides that come from uranium and oil-extracting industries are of the highest radiation hazard for population and environment.
Surprisingly, these conclusions made for one of the regions in Kazakhstan may be expanded to other parts of the country. Speaking about nuclear issues in Kazakhstan, we first of all recollect Semipalatinsk Nuclear Test Site (SNTS), but upon thorough consideration and based on authoritative opinion of the scientists involved in radio-ecological investigations there, one can also conclude that to a certain extent the situation is under control. Of course, huge efforts were made recently to make the situation there "near-stable".
Semipalatinsk Nuclear Test Site (SNTS)
According to official data, from 1949 to 1989 there were performed 456 nuclear tests with total 607 nuclear charges involved; among that there were performed 116 atmospheric nuclear tests (80 tests in air and 6 at high altitude), 30 surface and 340 underground tests including 4 underground excavational (with rock outbursts).
During recent years many research groups and scientific institutes studied character and scale of contamination at the test site. Scope of investigations is impressive while there are still minor parts of
the test site that has never been thoroughly investigated because of huge territories it covers. Lots of information is available resulted from performed and on-going research [13-24, 30]. According to character and contamination scale, sites of the polygon may be grouped into three characteristic types: areas with area contamination as a result of surface and atmospheric nuclear explosions sites contaminated by excavational and contingency underground explosions near-mouth sites of the wells with water effects.
Most concern there now is paid to the mountain range Degelen where 209 explosions were performed. Radioecological situation there is not stable and tends to worsening. Currently conservation (sealing) of pits where water flew out from is finished what to certain extend stopped further contamination of surface lands, but does not completely eliminate the hazard.
In places of excavational explosions and unexpected surface releases there are local spots of contamination with high concentrations of transuranium elements 239+240Pu and 241 Am and activation products 60Co, 152Eu, 154Eu, etc. Contamination there is mainly concentrated in cones formed due to explosions or close to them. As a rule, most of radionuclides is associated with large-grain soil fractions and is strongly chemically bound there. Therefore, the radio-ecological situation there is stable and all what is required to do is to prevent access to those places. Remediation measures there would be needed if the lands are needed for commercial or agricultural activity.
Ground and air tests resulted in contamination of considerable territories, but its average rate is not high approaching, for most of the territories, several thousands Bq/kg. There are no primary contaminators with several same-rate concentrations of decay products such as 90Sr and 137Cs or residual plutonium isotopes. Specialists consider some administrative restrictions for types of commercial activities at these territories enough.
Considerable time has passed since the polygon was closed. By now activity of strontium-90 and cesium-137 has decreased twofold, but the alpha-activity of plutonium remains almost the same.
There is growth of commercial activities at the site with active exploration of mineral resources at Karazhara and Zhaksytyz Lake, geological prospecting and some agricultural activities. Radio-ecological situation in Kazakhstan - main conclusion
Radio-ecological investigations performed within various State programs since 1992 [12] have confirmed that a priori concerns about extremely unfavorable radio-ecological situation in the Republic of Kazakhstan. Not all the territory of the republic was subjected to comprehensive radio-ecological investigations. At investigated territories were revealed contaminations with radionuclides of different environment components with contamination spot sizes ranging from hundreds square meters to several thousand square kilometers. Annual effective dose at those areas varies from the values that require establishing continuous monitoring over environment and sites to the values that require removal of local population from contaminated territories in accordance with Radiation Safety Norms NRB-99 [32].
Public concerns
In the beginning of 2004 we made a brief survey trying to determine the extent of international public attention to nuclear-related issues compared to other events in our country. In analytical papers published during last 4 years (2000-2004) in electronic journal Analyst by Central Asia-Caucasus Institute of the Johns Hopkins University Kazakhstan was mentioned 210 times; in those papers radio-ecological issues were mentioned 4 times and only 2 papers were somehow devoted to these issues: "Kazakhstan's Semipalatinsk Relief and Rehabilitation Program" "KazAtomProm is Lobbying for Importing Nuclear Waste"
Nuclear-related public concerns within the country are of much greater scale. A good indicator might be recent discussions on the import and disposal in the region of Kazakhstan of intermediate- and low-level radioactive waste.
The idea was to import foreign low-level waste to cover expenses for disposal of our own radioactive waste. Assessments show that amount of radioactive waste in Kazakhstan is hundreds of thousands tons and money required to dispose it properly, as reported to the Kazakhstani Parliament,
exceeded $1,110,000,000 USD; such tremendous expenses are absolutely unaffordable for Kazakhstan. A large portion of this waste was generated during Soviet times and after the USSR collapse, Kazakhstan was left alone to solve the waste problem. According to current Kazakhstani legislation, import of nuclear waste is prohibited. Recently, public discussions were very active.
For instance, a popular talk-show at State TV channel "Khabar" gained interesting statistics. During TV-debates there was a tally of telephone calls from people who support or refuse the idea of waste imports. The total number of calls was 482; 239 of them voted "FOR" and 243 were "AGAINST" the idea. As well, for our city ~500 calls for 40 minutes is a very big number, for example another episode of this show discussed issues of corruption in upper-level authorities collected only about 200 calls [29].
Discussion of these issues was not hindered and by now is the only example in Kazakhstan when the authorities did not interfere with public discussions and followed the public will.
Radiation Exposure - general case
Entire nature of radiation makes "zero exposure" impossible. Nuclear science and technology when refer to safety assurance widely operate with the principle ALARA - "as low as reasonably achievable" which implies decrease of exposure levels from artificial sources to the lowest possible levels. At the same time radiation is an inalienable part of our existence. According to IAEA data, average doses gained by people on the Earth are accumulated due to the following factors: 72.999% is exposure from natural radiation, 20% - from medical diagnostics, 7% due to influence from nuclear explosions performed worldwide and 0.001% of the total dose gained by a person is due to activity of nuclear power plants.
For instance, transcontinental flight at altitude 9,000 m results is a dose accumulation comparable with x-ray examination. This dose is gained at high altitude where Earth's atmosphere and, depending on geographical latitude, magnetic field have much lower protective action against cosmic radiation.
Doses gained from natural background radiation depend on geographical location of a place -content of radioactive isotopes in the earth's crust and rock formations - and geographical latitude that defines cut-off rigidity for cosmic rays that reach earth's surface.
Radioactive Fallouts
Another contributor to continuous irradiation is radioactive fallouts distributed as spots over earth's surface:
At explosion of nuclear weapons in close to the earth's surface, the detonation pulverizes surface material and sucks much of it into the hot mass that rises as a mushroom cloud. Inside the fireball and stem of the bomb cloud the radioactive particles become attached to heavier particles. Depending on the size/mass of formed bits of matter they fall back to earth within minutes, hours and much longer periods of time, forming different type fallout. Microscopic particles sweep around the world in a zone at the latitude of the explosion and are brought to earth with precipitations. If the detonation injects the bomb debris into the higher stratosphere, we refer to stratospheric, or global, fallout. Particles there may remain aloft for long periods of time and are scattered horizontally, spreading throughout the stratosphere.
During a nuclear explosion up to approximately 300 different radioactive isotopes are formed. Since many of them are extremely short-lived, the total radioactivity from the bomb decreases more than a hundredfold within the first hour after the explosion. But remaining long-living isotopes constitute the long-term radiation hazard primarily through contamination of the foods that are consumed by humans or inhalation with dust. From chemical point of view, radioactive isotopes are "indistinguishable"; radioactive strontium or potassium, for instance, are deposited in human bone and lead to a higher incidence of leukemia and bone cancer, and 131I (half-life of only eight days) becomes concentrated in the thyroid gland, where it causes thyroid cancer.
Conclusion
Beyond a description of current situation with radio-ecological issues in Kazakhstan we would like to make an inevitable statement that people in a modern world have to find ways to survive and live in conditions of increased radiation background and further development of nuclear technologies.
REFERENCES
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