ARTIFICIAL RADIONUCLIDES SPECIATION IN RIVER WATER OF DNIEPER BASIN

摘要

The speciation of Uranium fission product (paniculate, dissolved organic and dissolved inorganic matter) in the waters of the Dnieper and Prypyat Rivers was studied after the Chernobyl accident. The initial contamination of surface waters consisted predominantly of "hot" particle borne ~(90)Sr, ~(95)Nb, ~(95)Zr, ~(103)Ru, ~(106)Ru, ~(134)Cs, ~(137)Cs, ~(140)La, ~(141)Ce, and ~(144)Ce. Over 15 years the total radioactivity in water decreased due to sedimentation and radioactive decay. At the same time the fraction of dissolved ~(90)Sr and ~(137)Cs increased. This fraction has now reaches 99% and about 80% of ~(137)Cs and >95% of ~(90)Sr in river water occurs as cationic species. The remainder is distributed equally between suspended and dissolved organic matter. The transformation of suspended particle borne radionuclides into dissolved species is described by the equation: N_t = exp(-kt), where k is the transformation rate constant. Values of k were 0.126 y~(-1) for ~(137)Cs and 0.241 y~(-1) for ~(90)Sr. The specific activity of the suspended paniculate matter in river waters reached 15 kBq kg~(-1) for ~(137)Cs and 700 kBq kg~(-1) for ~(90)Sr. The cationic species represent the main part of the fission products that are transported into the Black Sea. 6·10~(11) Bq for ~(137)Cs and 7·10~(12) Bq for ~(90)Sr are transported as dissolved species from the Exclusion Zone into the Black Sea. From the geochemical point of view we presently face the most dangerous period of radionuclide mobilization by the formation of dissolved ionic species.