It is known that the radioactive contamination of soil around "Ukryttya" object is concentrated basically on pre-accident surface, which was closed by clean soil layers during liquidation of the accident consequences. During building of foundations for New Safe Confinement a lot of boreholes were drilled for sheet piling. These boreholes were used for gamma-logging to assess soil contamination with radionuclides, forecast of radioactive waste quantities, which will appear after deleting soil from the pit, and doses to the staff at the reaching the active layer of soil. Measurements of a gamma-field have been carried out almost in five hundred boreholes. In processing of gamma-logging data in these boreholes increased values of exposure dose rate below the active layer and on the bottom of some boreholes were discovered. Such phenomenon could indicate on availability of additional contamination below active layer, which can be associated with moving of radioactive particles down through a borehole or with migration of ra-dionuclides deep into the soil from active layer. In this regard the new approach for interpretation of results was devel-oped and applied, namely unification of all gamma-logging chart by dividing each of them on its maximal value. Such method allowed to examine and compare of the gamma-logging results in different boreholes, including analyzing the nature and origin of additional contamination on the bottom of boreholes. As a result, it was found that the additional radiation below the active layer in most part of boreholes is completely explained by the strait radiation from active layer and by pouring out radioactive soil from upper layers to the bottom of boreholes.
Keywords:gamma-logging, boreholes contamination, radionuclides, object "Ukryttya".
1. Panasyuk M. I., Skorbun A. D., Pavliuchenko M. I. Applying of spectrometric gamma-logging to study the struc-ture of distribution of contamination in soil around 4th power supply of CNPP // Problemy Chornobylya (Prob-lems of Chornobyl). – 2003. – Iss. 13. – P. 116 - 119. (Ukr)
2. Skorbun A. D., Panasyuk M. I., Pavliuchenko M. I. Method for determining the specific activity of 137Cs in soils according spectrometric gamma-logging of boreholes // Problemy bezpeky atomnyh electrostantsiy i Chornobylya (Problems of nuclear power plants’ safety and of Chornobyl). – 2005. – Iss. 2. – P. 104 - 107. (Ukr)
3. Haikovych I. M., Shashkin V. L. Testing of radioactive ores by gamma radiation. Theory and methods. - Moskva: Energoatomizdat, 1982. – P. 158. (Rus)
4. Instruction of gamma-logging in prospecting and mineral exploration. – Moskva, 1987. (Rus)
5. Panasyuk M. I., Skorbun A. D., Pavliuchenko M. I. et al. Determination of recalculation coefficient fo gamma-logging of boreholes in terms of local area “Ukryttya” object // Problemy Chornobylya (Problems of Chornobyl) – 2004. – Iss. 9. – P. 105 - 109. (Rus)
6. Panasyuk M. I., Skorbun A. D. Theoretical description of borehole with active layer // Naukovi ta tehnichni aspek-ty mizhnarodnogo spivrobitnitstva v Chornobyli: zb. nauk. st. – Kyiv: Politehnika, 2004. – Iss. 14. – P. 56 - 58. (Rus)