Artificial Radionuclides Speciation in River Water of Dnieper Basin

Abstract

The speciation of Uranium fission product (particulate, dissolved organie and dissolved inorganic matter) in the waters of the Dnieper and PrypyatRivers was studied after the Chernobyl accident. The initial contamination of surface waters consisted predominantly of “bot” particle borne ⁹⁰Sr, ⁹⁵Nb, ⁹⁵Zr, ^l03Ru, ^l06RU, ¹³⁴CS, ¹³⁷CS, ¹⁴⁰La, ¹⁴¹Ce, and ¹⁴⁴Ce. Over 15 years tbe total radioactivity in water decreased due to sedimentation and radioactive decay. At the same time the fraction of dissolved ⁹⁰Sr and ¹³⁷CS increased. This fraction bas now reaches 99% and about 80% of ¹³⁷CS and >95& of ⁹⁰Sr in river water occurs as cationic species. Tbe remainder is distributed equally between suspended and dissolved organic matter. The transfonnation of suspended particle borne radionuclides into dissolved species is described by the equation: k _t = exp(-kt), where k is the transformation rate constant. Values of k were 0.126 y⁻¹ for ¹³⁷CS and 0.241 y⁻¹ for ⁹⁰Sr. The specific activity of the suspended particulate matter in river waters reacbed 15 kBq kg⁻¹ for ¹³⁷CS and 700 kBq kg⁻¹ for ⁹⁰Sr. The cationic species represent tbe main part of the fission products that are transported into the Black Sea. 6·10¹¹ Bq for ¹³⁷CS and 7·10¹² Bq for ⁹⁰Sr are transported as dissolvedspecies from the ExclusionZone into the Black Sea. From the geochemicalpoint of view we presentlyface the most dangerous period of radionuclide mobilizationby the fonnation of dissolved ionic species.