¹³⁷Cs Pollution of Lake Onega and Its Purification

A sorption–diffusion model of ¹³⁷Cs absorption by bottom soils has been used to forecast ¹³⁷Cs concentration in global fallouts and emergency release from the Chernobyl NPP in water of the deep (H_av = 30 m) Lake Onega. The natural conditions and the morphohydrological characteristics of the lake caused a rapid (2–3 years) transformation of ¹³⁷Cs-polluted water to pseudoequilibrium concentrations. For 56 years (from 1964 to 2020), the concentration of ¹³⁷Cs in water was determined with acceptable accuracy by a sorption-diffusion model of ¹³⁷Cs adsorption by bottom soils with coefficients of sorption K_d = 4000 L/kg and diffusion D = 1.0 × 10^–7 cm²/s. The effect of water exchange in the lake on ¹³⁷Cs migration is taken into account in the characteristic of conditional exchange of Lake Onega water W = 16.4 years. The correctness of the forecast of water pollution by ¹³⁷Cs was verified by comparison with experimental data and the conditions of ¹³⁷Cs pollution of the waters of deep lakes in the northwestern Russia and Finnish Lapland.