Chernobyl accident activity release

The activity ratio Pu/ Pu varies depending on source term such as weapon plutonium, fallout from nuclear tests, the Chernobyl accident and releases from nuclear fuel reprocessing plants. The objective of this project was to investigate if there was any close fallout over Madagascar even if it was claimed that all Pu was evaporated in the upper atmosphere. 

The activity of137Cs in the fuel which melted was 250 TBq (Chamber-lain, 1981), and if the 137Cs released and passing the stack filter was about 80 TBq, this represents about 30% of that in the melt zone. In the Chernobyl accident, an estimated 13% of the total inventory of137Cs in the reactor was emitted (U.S.S.R. State Committee, 1986). 

The release of 131I and other fission products in reactor accidents has been considered in the previous chapter. In the Windscale accident, the temperature in the fire zone reached an estimated 1300°C and 8 tonne of uranium metal melted. Over 25% of the 1311 in the melted fuel escaped to atmosphere. In the Chernobyl accident, the fuel was U02, the temperature exceeded 2000°C, and about 25% of the total reactor inventory of 131I was released to atmosphere, as vapour or particulate aerosol. In the Three Mile Island accident, 131I remained almost completely in the reactor coolant. The activities of 131I released in reactor accidents, including that at Chernobyl, have totalled much less than the activities released from weapons tests (Table 2.3). 

Strontium released into the atmosphere from natural and anthropogenetic activities is transported and redeposited on the earth by dry or wet deposition. Dry deposition results from gravitational settling, impact, and sorption on surfaces (NCRP 1984). Experimental data on dry deposition of strontium, present in the ambient atmosphere, is limited. Rain, sleet, snow, or other forms of moisture can wash airborne particles containing strontium from the atmosphere by the process of wet deposition. Wet deposition depends on conditions such as particle solubility, air concentration, rain drop size distribution, and rain fall rate (NCRP 1984). Hirose et al. (1993) examined the mechanism of aerial deposition of 90Sr derived from the Chernobyl accident, and found that 96% of atmospheric 90Sr returned to earth as wet deposition. 

Military uses (fission bombs based on U) and accidental releases of radionuclides such as during the Chernobyl accident may lead to the contamination of large areas. However, the contribution of uranium and its decay products to the radiotoxicity of nuclear fallout is marginal. Most of the acute and protracted dose is caused by relatively volatile and soluble fission or activation products such as Sr, Cs... 

At a result of the Chernobyl accident significant amounts of radioactivity were released into the environment, but most of radionuclides fell out not in the Arctic re-gion. Nievertheless some Cs has been deposited and transferred there. By some estimates, Chernobyl fallout contributed 1-2% of the total 1991 Cs concentration in the Arctic basin [OTA, p. 37]. Contribution of Cs as a product of industrial activity (including fallout from the Chernobyl accident) into the dose exposure from the ground surface, is less than 10-15% [Arctic, p. 24]. 

Half-lives span a very wide range (Table 17.5). Consider strontium-90, for which the half-life is 28 a. This nuclide is present in nuclear fallout, the fine dust that settles from clouds of airborne particles after the explosion of a nuclear bomb, and may also be present in the accidental release of radioactive materials into the air. Because it is chemically very similar to calcium, strontium may accompany that element through the environment and become incorporated into bones once there, it continues to emit radiation for many years. About 10 half-lives (for strontium-90, 280 a) must pass before the activity of a sample has fallen to 1/1000 of its initial value. Iodine-131, which was released in the accidental fire at the Chernobyl nuclear power plant, has a half-life of only 8.05 d, but it accumulates in the thyroid gland. Several cases of thyroid cancer have been linked to iodine-131 exposure from the accident. Plutonium-239 has a half-life of 24 ka (24000 years). Consequently, very long term storage facilities are required for plutonium waste, and land contaminated with plutonium cannot be inhabited again for thousands of years without expensive remediation efforts. 

Nuclear activities such as electricity production by nuclear power plants, or accidents such as occurred at Chernobyl, release radionulides, including caesium, into the environment. The caesium concentrations in these matrices is very low, so that in addition to a sensitive analytical method, it is necessary to make use of an enrichment technique to bring the caesium concentration within the scope of the analytical method. 

The accident at Chernobyl Nuclear Power Plant and considerable release of radionuclides in particulate fraction renewed interest in hot particles (HPs)—tiny objects of pm dimensions, having density of activity comparable with the one of irradiated nuclear fuel. They pose radiological risk, especially when inhaled with the air after resuspension from the soil. Studies (Osuch et al., 1989 Piasecki et al., 1990), performed on a quite large set of HPs (over 200 species) collected in Autumn 1986, indicated the existence of two, roughly equally populated groups of HPs ... 

Small amounts of Cs and Cs are released into the environment during nearly aU nuclear weapon tests and some nuclear accidents, most notably the Chernobyl disaster. It is weU documented that mushrooms, including edible species from contaminated forests, accumulate radionucHdes (mainly Cs) in their fungal sporocarps. For example, the edible mushroom commonly known as penny bun, porcino or cep [Boletus edulis) from Poland (1987) showed about seven times higher activity of Cs in comparison with the radioactive background and about double the activity... 

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