O. S. Lagunenko, V. E. Khan, O. O. Odintsov, O. K. Kalinovskiy,
V. P. Kovalchuk, T. A. Kravchuk, O. V. Filippov, M. M. Popov
Institute for Safety Problems of Nuclear Power Plants, NAS of Ukraine,
36a, Kirova st., Chornobyl, 07270, Ukraine
Data on the radionuclide composition, volume activity and dispersity of radioactive aerosols taken in 2017–2018 in room 012/15 of the Shelter object, into which the lava-like fuel-containing materials (LFCM) flew after the accident, are presented. Relative air humidity in the room 012/15, depending on a year season, was varying from 50 to 97%. During a day, sometimes it was changing at 5–10%. High humidity (about 93–97 °C) was registered in summer period, when mean daily temperature in the environmental air reached 24–27 °C. In majority of cases, relatively small value of air humidity corresponded to high concentration of radioactive aerosols. High humidity values coincided in time with low values of radioactive aerosol concentrations. Mean daily temperature of room 012/15 air was relatively stable during all survey period. After cold period of year came, it dropped from 12 to 7 °С, and in warm period, when the Shelter object was heated, it grew up to 11–12 °С. Such a mode was provided by a huge mass of concrete and metal structures of the Shelter object, and due to the fact that the room 012/15 is located at height elevation +3.00, where air exchange is negligible. It was stated that concentration of beta-radiating aerosol-carriers (90Sr + 90Y and 137Cs) was fluctuating with the range 0.025–4.5 Bq/m3. Besides, 137Cs share made 54%. Gamma-spectrometry measurements and radiochemical analyses have demonstrated that average ratios of semi-volatile radionuclide-products of Chornobyl Nuclear Power Plant Unit 4 accident in aerosol samples comply with LFCM content in the Shelter object rooms. It testifies that LFCM destruction and particular transfer of materials in aerosol state occurs. Their carriers were the aerosols with activity median aerodynamic diameter (AMAD) larger than 4 µm. During 2017–2018, aerosols in room 012/15 were enriched by 137Cs relatively to LFCM located in this place, as it was observed earlier. The sources of additional cesium are 137Cs aerosol-carriers producible, apparently, as result of destruction of surfaces, on which, particles-carriers of condensation cesium were sorbed earlier. Their carriers were the aerosols with AMAD 1 µm.
Keywords: Shelter object, aerosols, volume activity, lava-like fuel-containing materials, radionuclide ratios, dispersity.
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