| Abstract [eng] |
Investigations on the determination of 137Cs sources in the Ignalina NPP environment air and the evaluation of changes of the long-term trend of 137Cs activity concentrations in the Ignalina NPP ground-level air were carried out in this dissertation. Radionuclide activity concentrations in the air and deposition were measured in the Ignalina NPP impact zone in 2004-2009. Results show, that in recent years annual 137Cs activity concentrations in the ground-level air in the Ignalina NPP region change with the half-time of 30 years. Observed episodic increases in 137Cs activity concentrations in the air correlate well with air mass transport trajectories that intersect territories, polluted with 137Cs after the accident at the Chernobyl NPP. The growth of radioactive aerosol particles in the oversaturated water vapour of the operating RBMK reactor has been investigated. In the one contour nuclear power plant coolant water steam, noble gas radionuclides decay into alkaline and earth-alkali metals, which become condensation nuclei and due to the absorption of water molecules in several minutes grow into radioactive aerosol particles. The classical method of the radionuclide activity determination in aerosol particle samples, collected on filters, was supplemented with experiments on the leaching of aerosol particles using the distilled water and measurements of radionuclide activities in samples before and after the experiment. Results show that the quantity of 137Cs and 60Сo in the soluble fraction of aerosol particles, collected in the ventilation air of the operating reactor, was 74 22 % and 67 17 %, respectively, and that in the ventilation air of the shut-down reactor was 24 5 % and 20 5 %. The distribution of the 60Co activity concentration in the NPP plume was calculated by supplementing the semi-empirical Pasquill-Gifford equation with the coefficient, which describes the change in the ratio of soluble and insoluble aerosol particles, 60Co carriers, in time and space. |
