Сибирский лесной журнал (Dec 2017)
The migration of 137Cs and 90Sr in soil-vegetation cover at accidental underground nuclear explosion site «Kraton 3»
Abstract
Here, we report studies on content and distribution of 137Cs and 90Sr artificial radionuclides in soil-vegetation cover at «Kraton 3» accidental underground nuclear explosion site. This site is located in the territory of northwestern Yakutia, within the northern taiga subzone of the permafrost-taiga region of eastern Siberia boreal belt. In geomorphological aspect, this object belongs to steep slope of the divide connecting the flood-lands of the Markha River and peneplain of the divide. Sod-carbonate (redzina) soils prevail in soil cover of «Kraton 3» underground nuclear explosion site. This type of soil is typically characterized by a thin soil profile, weak alkaline reaction, heavy granulometric composition, saturated soil-absorbing complex, and drastically decreasing profile distribution of humus. Despite the considerable time after the accident, the radiation situation at the site is still very disturbing. Gamma ray background radiation levels at the site varied from 10 to 200 μR/h, which were 2–25 folds higher than average natural background radiation. The isotope contamination densities in soils of sites interconnected along the drainage were 34–1025 kBq/m2 for 137Cs and 57–781 kBq/m2 for 90Sr, which exceeded 30–1000 times the global fallout levels of these radionuclides. The rates of vertical migration of studied radionuclides were also determined as 0.11–0.84 % (137Cs) and 0.79–1.44 % (90Sr) per year of total radiation contamination density. The minimum vertical migration rates of 137Cs (0.11 %) were observed in leached sod-carbonate soil, while maximum rates (0.84 %) were determined in immature sod-carbonate soil, the profile of which lacks organogenic and humus-accumulative horizons. The migratory capabilities of 137Cs and 90Sr in this soil were very close and made 0.84 and 0.79 % respectively. Migration factors of 137Cs and 90Sr in permafrost soils of the studied area were determined with the use of principal component analysis. This study also revealed that radioactive contamination levels of local vegetation remain considerably high. The concentration of radioactive cesium in plants growing on the site of accidental underground nuclear explosion is 40–5000 times higher than its natural background levels.
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