THE NATURE OF CONTAMINATION OF THE AREA IN THE NEAREST VICINITY OF CHORNOBYL NPP DESTROYED UNIT

摘要

A territory around the destroyed by the 1986 accident 4-th unit of ChOrnobyl NPP has been contaminated severely by radioactive materials pollution from the damaged unit. During the stage of accident consequences mitigation, the radioactive materials in a form of fragments of building constructions, fuel elements, graphite cladding, and upper layer of soil have been collected and buried. Around the destroyed Unit 4 the "Shelter" have been erected, and the decontaminated territory was covered by such anthropogenic soils as a pure crushed stone, sand and poured concrete. Special investigation indicates, however, that those soils turned out to be contaminated as well, and the main amount of the whole activity is concentrated in the so called active layer of the soil, which is located close to the pre-accident earth surface level. Given report is devoted to a possible mechanism of the soils contamination and radionuclide distributions in soils by way of laboratory analysis of cores of wells, which were drilled in the local zone, and gamma logging data analysis as well. The performed sampling analysis of soils, which belongs to the Shelter object industrial site show that radioactive contamination of anthropogenic soils of the active layer is mainly originates from active impurities (fine dispersed fuel particles) being distributed in a uniform way in the soil volume. The industrial site territory is covered by a concrete of a noticeable specific activity. That concrete during construction of "Shelter" flowed out through chinks in the casing and spread over the surrounding site. The concrete leached small fuel particles and carried those particles away from obstruction in mechanical way. This turned out an effective and power enough mechanism to contaminate the industrial site by radionuclides already just after an active stage of the accident.