🗊Презентация Radionuclides in the Arctic

Lecture №4 Radionuclides in the Arctic.

Radioactivity Radioactivity is the property of spontaneous disintegration, or decay, of atomic nuclei accompanied by the emission of ionizing radiation. Activity corresponds to the number of disintegrations per second of an isotope (with dimensions T –1).

Radioactivity The SI (Standards Internationaux) unit of activity is the reciprocal second (s –1 ) with the name Becquerel (Bq). The older, non-SI, unit Curie (Ci) that was derived from the (presumed) activity of one gram of radium and is still used in some fora, corresponds to 3.7*10 10 Bq.

Units and abbreviations

Radiation doses – a comparison

Natural radioactivity Natural radioactivity is derived from the decay of nuclei in the Earth’s crust and by the bombardment of the Earth by cosmic radiation producing radionuclides in the Earth’s atmosphere. These natural radionuclides fall into three categories: the very long-lived primordial radionuclides (40 K, 238 U, 232 Th, 235 U) formed at the time the Earth was created; decay chain radionuclides (radionuclides in the uranium, thorium and actinium decay series) that are the products of decay of primordial nuclides; and cosmogenic nuclides produced by the interaction of high energy cosmic radiation with the Earth’s atmosphere (e.g., 3 H, 7 Be, 14 C, 22 Na).

Artificial radioactivity. In most situations, the most radiologically important fission products in the short term are 89 Sr, 90 Sr, 131 I and 137 Cs, and in the long term, 90 Sr and 137 Cs, because of their yields, half-lives and chemical properties. Activation products are the isotopes formed principally by the capture of neutrons by stable isotopes in high neutron flux environments.

Radioactivity in the Arctic Radioactivity in the Arctic have highlighted that the Arctic terrestrial environment is more vulnerable to radioactive contamination than many other parts of the world. Moreover, they have shown that past sources such as fallout from nuclear testing in the 1950s and 1960s and the 1986 accident at the Chernobyl nuclear power plant still contribute to human exposure. Radioactivity in the Arctic is a concern because contamination can persist for long periods in soils and some plants and because pathways in the terrestrial environment can lead to high exposures of people.

Radioactivity in the Arctic The sources of radioactive contamination in the Arctic can be divided into past contamination sources and potential future sources.

Past contamination sources Past fallout remains in the terrestrial environment. From a circumpolar perspective, fallout from past nuclear weapons testing has historically been the most important source of human and environmental exposure to anthropogenic radioactive contamination. Other past significant emissions include fallout from the 1986 accident in the Chernobyl nuclear power plant, which affected the European Arctic. Although the fallout spread all over the globe, the Arctic is particularly vulnerable because Arctic vegetation has very efficient uptake of radionuclides. Potential sources of radioactive contamination of the Arctic include nuclear powered vessels that were poorly maintained or being decommissioned; dumped and stored radioactive wastes, including wastes stored under inadequate conditions; radioisotope thermoelectric generators (RTG s) used as energy sources in northern regions; and nuclear power plants and reprocessing facilities located close to the Arctic.

Primary (P) and secondary (S) sources of artificial radionuclide contamination in the environment

Radioactivity in the Arctic Radioactive contamination of the Arctic has occurred at two different scales: 1. Widespread contamination, such as that associated with global nuclear weapons testing, Sellafield releases and the Chernobyl accident. 2. Localized contamination of smaller areas (e.g., resulting from the Thule nuclear weapons accident and radioactive wastes dumped at sea). The following presentation focuses on 137 Cs and 90 Sr, since these radionuclides are important for determining dose to humans, and considerable data exist on each of them.

Widespread contamination of land and sea Terrestrial contamination The two major sources of fallout in the Arctic region have been nuclear weapons testing and the Chernobyl accident. Marine contamination The anthropogenic sources contributing to the contamination in the marine environment are mainly nuclear weapons fallout and releases from Sellafield and the Chernobyl accident.

Localized contamination Short-range fallout from Novaya Zemlya tests There have been some 130 tests at Novaya Zemlya, 88 in the atmosphere, 3 underwater and 39 underground

Sources 1. Nuclear tests 1945 - 1990 According to the UNSCEAR 2000 (UNSCEAR 2000), after 1945, 2,419 nuclear explosions were conducted with a total yield equivalent to 530 Mt. The main overall yield (440 Mt) was primarily due to 543 atmospheric nuclear explosions, while 1,876 underground nuclear explosions produced only 17% of the total yield (90 Mt). The most powerful atmospheric nuclear explosions (4 MW in excess of their power) are responsible for almost 66% of the total yield. The largest nuclear test in the atmosphere was an explosion with a capacity of 50 megatons, carried out on October 30, 1961 on Novaya Zemlya. The largest underground explosion on Novaya Zemlya (from 1.5 to 10 Mt) was carried out on October 27, 1973.

Of 130 explosions conducted on Novaya Zemlya: 85 were atmospheric, 3 - underwater, 2 - at the surface of water, 1 - on the surface of the earth, and 39 - underground. Approximately 12% of the radioactive products of the explosions on Novaya Zemlya fell outside the test sites, 10% of deposition fell into the concentric circumpolar ring at the latitude of Novaya Zemlya, and 78% in the form of fine dispersed products replenished the global fund of stratospheric radionuclides, from which further radioactive fallout occurred (AMAP 1998).

Sources 2. The Chernobyl accident of 1986

Sources 3. Western European radiochemical plants for processing nuclear fuel. At radio chemical plants, uranium and plutonium are separated from spent nuclear fuel for reuse, which is accompanied by the formation of a large number of various radioactive waste (UNSCEAR 2000). The most powerful and currently operating plants in Western Europe are Sellafield (Great Britain) and La Ag (France). Discharges Sellafield through the pipes fall into the Irish Sea, and discharges RHZ on Cape La Ag in the Channel English Channel.

Sources

Sources 4. Radiochemical plants of Russia Currently, there are five Rosatom nuclear fuel cycle plants that can influence the water environment of the Arctic seas. The main ones are Mayak complex in Chelyabinsk Oblast (Ob River basin), Siberian Chemical Plant Tomsk-7 in Tomsk Oblast (Ob River Basin), Krasnoyarsk Mining and Chemical Combine in the Krasnoyarsk Territory (Yenisei Basin) (AMAP 1998).

Sources 5. The Russian nuclear fleet (including the service infrastructure) In total: nuclear submarines - 248, surface nuclear ships - 5, nuclear icebreakers - 8, The total number of nuclear reactors installed at these facilities exceeded 450, and their total capacity is comparable to the installed capacity of all nuclear power plants of the country (Strategic 2004).

Sources 6. Kola and Bilibino nuclear power plants,

Sources 7. Radioisotope thermoelectric generators (RTGs) A special source of possible radiation impact on the Arctic coast is the so-called radioisotope thermoelectric generators. RTGs are used for long-term autonomous power supply of lighthouses and luminous navigation signs. In total, about 1000 RTGs were placed in Russia, mainly along the coast of the Arctic Ocean. The period of their production continued from 1976 to 1990. The service life of all types of RTGs is 10 years. At present, for all RTGs the service life has been completed

Sources 8. Underground nuclear explosions for economic purposes In the period from 1965 to 1988, the USSR carried out an extensive program of surface nuclear explosions for economic purposes. A total of 116 explosions were conducted. In general, the tasks of mining, oil and gas and construction industry were solved.

Sources 9. Elevated levels of natural radionuclides during offshore oil and gas production

SOURCES OF RADIOACTIVE WASTE The following categories: High-Level Waste (HLW)— Uranium mining and mill By-product material Low-Level Waste: - Class A - Class B - Class C - Greater Than Class C (GTCC) Formerly Used Sites Remedial Action Program (FUSRAP) Naturally Occurring Radioactive Material (NORM)

Movement of radioactive materials

Atmospheric transport The mean residence time of radionuclides in the Arctic stratosphere is in the order of one year. The transfer of radionuclides from the stratosphere to the troposphere occurs preferentially in the spring, when the tropopause is most ‘permeable’ The mean residence time of radionuclides in the troposphere is only a few weeks. Radionuclides in the troposphere are transferred to the surface of the Earth as wet or dry fallout.

Marine transport Releases into Arctic marine ecosystems can either occur directly, through routine releases from nuclear reactors into cooling water streams, leakage from dumped solid wastes, direct dumping of liquid wastes, or indirectly via atmospheric deposition. In addition, radionuclides released else where may be transported into Arctic marine systems.

Terrestrial transport Once radionuclides are deposited onto the Earth’s surface, their subsequent behavior is dependent on a number of factors including their physico-chemical form and the type of environment into which they have been released. Terrestrial and freshwater environments generally receive most of their radioactive contamination through precipitation (wet fallout). Vegetation may be contaminated directly by deposition of the radionuclides onto the surface of the plants, or indirectly by uptake from the soil through the roots. Further transfer of radionuclides in the food chain occurs when animals, including humans, consume food, drink water or breath air.

Transfer Interception Soil-to-plant transfer Plant-to-animal transfer Diet selection Availability for absorption in the gut Metabolism of the radionuclide

Half-life of a radionuclide The effective biological half-life of a radionuclide in an organism is a function of both the biological half-life of the element in the organism and the physical half-life of the radionuclide. 1/T 1/2 eff-biol = 1/T 1/2 biol + 1/T 1/2 phy The effective ecological half-life of a radionuclide is a function of both the half-life of the element in a component of an ecosystem and the physical half-life of the radionuclide. 1/T 1/2 eff-eco = 1/T 1/2 eco + 1/T 1/2 phy

The half-life of a radionuclide

Freshwater pathways The transfer of radionuclides from such systems occurs mainly through consumption of freshwater fish and from exploitation as drinking water. The mobility of a radionuclide depends on its ability to bind to river sediments and its competitive interactions with other ions. Strontium is one of the more mobile elements in aquatic systems because it does not bind strongly to sedimentary material.

Marine pathways Exposure from marine pathways arises from the consumption of marine food products, including fish and shellfish, mammals such as seals and whales, and seaweed. In general, contamination of marine biota is much less than that arising from terrestrial pathways, largely because of the strong sorption of many radionuclides by aquatic sediments and also because of the enormous dilution which occurs in marine water bodies

The effects of radiation under Arctic conditions: Severe climatic conditions are factors of natural environmental stress, restricting the number of biological species which are able to survive in the Arctic. Low biodiversity is a negative ecological factor associated with the low capacity of Arctic ecosystems to adapt in the case of any environmental changes. The development of radiation effects in the Arctic poikilothermic (or hibernating) organisms is expected to occur more slowly, because of low environmental temperatures. On the other hand, repair of radiation damage in cells and tissues is not effective at very low temperatures. Lesions in the cooled (poikilothermic or hibernating) organisms are latent. However, if organisms become warm, lesions are rapidly revealed. As a result, radiation effects may not appear during the winter period, but may manifest themselves intensively during the warm season.

The effects of radiation under Arctic conditions Development of embryos and young poikilothermic organisms in the Arctic occurs slowly; High concentrations of lipids in Arctic animals may be expected to increase their radiosensitivity, because chemical products of lipidoperoxidation produced by irradiation are toxic for organisms. Long-distance migrations of Arctic animals, in general, are favorable for survival, because animals do not stay within any contaminated local area for long periods; thus accumulated doses to migratory animals are expected to be lower than those for sedentary organisms.

The effects of radiation morbidity (e.g., worsening of physiological characteristics of organisms; effects on immune system, blood system, nervous system); reproduction (negative changes in fertility and fecundity, resulting in reduced reproductive success); mortality (shortening of lifetime as a result of combined effects on different organs and tissues of the organism); cytogenetic effects (radiation effects at the cellular level); ecological effects (changes in biodiversity, ecological successions, predator-prey relationships); stimulation effects (radiation hormesis, low dose stimulation effects); and adaptation effects (responsive adjustments of organisms to the conditions of chronic irradiation).