ИСТИНА

The radioactive contamination of the vast territory in the Eastern Europe, formed after the Chernobyl accident, is inevitably transformed in connection with two main causes. The first factor is process of radioactive decay, contributing to a constant reduction of radionuclides` content in the environment. Secondly, due to the processes of denudation and accumulation, its lateral migration takes place, which is expressed in the transport of 137Cs together with the soil particles on which it is sorbed. This leads to an accelerated reduction of 137Cs inventories in the areas of prevalence of erosion processes and accumulation in the areas of accumulation (Panin et al., 2001; Golosov et al., 1999, 2000, 2013; Walling et al., 2000; Belyaev et al., 2013). The flux of 137Cs with sediment yield is supposed to the main factor of secondary hazards for the territories, which were not affected by Chernobyl accident, but adjacent to the zone of intensive contamination The Upa River basin was explored. This river in its upper reaches crosses territories of intensive radioactive contamination – so called “Plava radioactive spot”. Sediment yield formed in the upper reaches of the Upa River predominantly accumulate in the Shchekino reservoir, created near the Shchekino power plant in town Sovetsk, located to the south of Tula. Therefore, this part of the basin and reservoir are very convenient study area for estimating of sediment and 137Cs budget. A number of cores of sediments were collected in Shcheckino reservoir in February of 2018 and analysed via gamma-spectrometry to recognize content of 137Cs. The analysis of 137Cs along the cores revealed that after Chernobyl accident it was very intensive accumulation of highly contaminated sediments. The growth of 137Cs inventories was more than 5 time higher than inventory constituted by direct fallout from atmosphere. Hence, Shchekino reservoir represents a potential radiation hazard in case of its deconstruction and flushing of contaminated sediments.