Radionuclide speciation in sediments of the Yenisei River

Institute of Biophysics Siberian Branch Russian Academy of Sciences, 660036 Krasnoyarsk, Russia

Abstract

The examination of sediment samples collected from the Yenisei River revealed the presence of artificial radionuclides characteristic of radioactive discharges from the MCC facility: isotopes of europium (¹⁵²Eu, ¹⁵⁴Eu, and ¹⁵⁵Eu), cesium (¹³⁷Cs and ¹³⁴Cs), ⁶⁰Co,⁹⁰Sr, and transuranium elements. Radionuclide concentrations in sediment layers remained high as far as 240 km downstream of the MCC. The vertical distribution of radionuclides in sediment cores was very complex, and down-core variations were due to different amounts of radionuclides released by the MCC and due to variations in the hydrologic conditions in the river. Sequential extraction performed on samples of the upper layers of the sediment core showed different degrees of potential environmental availability of artificial radionuclides: the amounts of extracted ⁹⁰Sr, ¹⁵²Eu and ²⁴¹Am were the largest (60–80% of initial activity), then followed ⁶⁰Co (30%), ^238,239,240Pu (15–30%), and, last, ¹³⁷Cs (5–15%). The distribution of ²³⁸U among chemical fractions of sediments was similar to that of ⁶⁰Co and ^238,239,240Pu: 30–40% of ²³⁸U initial activity was extracted. In a few samples, ²⁴¹Am was present in the unextractable form, which may be accounted for by the presence of microparticles of the reactor fuel.