Bottom sediment of the Kyiv Reservoir

The total inventory of 137Cs and 90Sr in the bottom sediment of the Kyiv Reservoir has gradually reduced since 1990. This is due to radioactive decay which dominates natural attenuation processes and surpasses the annual radionuclide intake associated with the river’s runoff inlet and is also due to partial removal of radionuclides from the water to the bottom sediment due to adsorption sedimentation processes.

In the first decade following the accident, approximately 70% of U7Cs and 90% of i°Sr total intake to the Dnipro reservoir system was accumu­lated by the bottom sediment of the Kyiv Reservoir and, in particular, in its upper section, which accepts the major part of the inlet from the Pripyat River sediment load.

Relocation of contaminated areas in the water area of the reservoir has been observed in recent years. The most contaminated fine silt particles have been suspended and transported to the middle and lower parts of the Kyiv Reservoir, where these particles are re-deposited. On the other hand, natural attenuation processes are also taking place. The contaminated sedi­ment is being covered with a layer of less contaminated material. In the next decade, sedimentation will play a dominant role in creating a relatively clean sediment layer above the buried radioactive contaminated particles in the deepest areas of the Kiev reservoir.

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