Abstract.The article presents the materials of radioecological studies of the authors on the accumulation capacity of bottom sediments in relation to radioactive substances entering the Southern Bug River during discharges from the South Ukrainian NPP. The aim of the study was to investigate the properties of bottom sediments in the channel reservoirs of the lower reaches of the Southern Bug River (Tashlyk and Oleksandrivske reservoirs) in terms of radionuclides retention.

The article analyses the content of radionuclides in water and bottom sediments of the Tashlyk and Oleksandrivske reservoirs. The coefficients of accumulation of radionuclides in the bottom sediments of these reservoirs were calculated. Differences between the Tashlyk and Oleksandrivske reservoirs were found in a number of hydrochemical parameters: temperature, hydrogen, alkalinity, dry residue, and dissolved oxygen. It is shown that these differences between the hydrochemical differences of the Tashlyk and Oleksandrivske reservoirs determine significantly lower coefficients of radionuclide accumulation in the bottom sediments of the Tashlyk reservoir.  The presence of an inverse linear relationship between water salinity and the values of ¹³⁷Cs and ¹³⁴Cs accumulation coefficients in the sediments of the Tashlyk and Oleksandrivske reservoirs was established, and a regression equation was determined that allows estimating the accumulation coefficient of cesium radioisotopes in sediments depending on water salinity.