Cs in flood - plain soils of the Techa river

The Techa river was contaminated in 1949-1956 from the nuclear enterprise "MAYAK". The investigations were carried out in flood plain of the Techa river in 1992-1999. In the upper and middle parts of the river the basic contaminator is I 3 7 Cs; downstream more active is 9 0 Sr. Density of contamination of soils with 9 0 Sr down the river changes from 600 to 200 kBq/m , and that with 1 3 7 Cs from 2,000 to 80 kBq/m . Radionuclides content in soils of the central part of the flood plain (30-40 m from the river-bed) also decreases further from the discharge point 1-2 orders. The Techa flood plain may be considered to be a source of secondary radioactive contamination of the water ecosystem. We evaluated the absorption stability and water migration of radionuclides in its soils under experimental conditions. The main quantity of 9 0 Sr was in exchangeable (41-66 %) form. ! 3 7 Cs was in firmly fixed form (80-98 %). The study of radionuclides distribution in the liquid fraction of the soil showed that the main part of 9 0 Sr (84%) was found in gravitation moisture. 1 3 7 Cs (97%) was in a less mobile form of moisture which was connected with soil by capillary and sorption powers.