Kulich N. The investigation of radionuclide behavior in fuel-carrying materials in ChNPP based on new spectroscopic methods of registration

The thesis presents results of study of fuel-carrying materials formed in Chernobyl accident. In order to achieve this objective, a complex of spectroscopic methods was developed to register radionuclide activity and investigations radionuclide behavior on the territory of polygons situated in Chernobyl Exclusion Zone and Shelter Object ("Obyekt Ukrytiye"). Method for measurement of 90Sr was proposed. This method allows to define concentration of activity of 90Sr and 137Cs simultaneously as in laboratory as in field conditions. Radionuclide composition of fuel-carrying materials were collected inside of Shelter Object in 2009 - 2012 years. Radioisotope ratios was obtained for isotopes of Pu, 241Am, 154,155Eu, 90Sr and 137Cs, which are used for analysis of radionuclide behavior in environment near ChNPP. Alpha-spectrometic investigations of fuel-carrying materials was done. Data on isotopes ratio were obtained for 233,234,238U, 238-242Pu,241-243Am, 243,244Cm. First part of 243Cm was defined from data of ?- and ?- spectrums in summary activity of curium in fuel-carrying materials. Concentration of radionuclide was measured in soil samples picked up near Shelter Object (more then 200 measurements). Behavior of 90Sr, 137Cs, 241Am and Pu isotopes was studied in soil layers till 60 cm depth. First 241Am was registered in spectrums of samples till 60 cm depth in all automorphic soils. Correlation of 90Sr and 241Am activities is defined, that demonstrate considerable contribution of fuel component in fallout. It is shown that radionuclides can be put abreast 90Sr > 137Cs > 241Am > Pu in correspondence with their migration mobility in mineral soils with normal water regime. Migration of Pu isotopes is found out comparable with migration of 241Am and 154Eu in some samples. Presence of U isotopes was registered in upper first and second layers till 4 cm depth. Ecological halftime periods of decontamination were calculated for layer of 5 cm soil based on data collected near Shelter Object about radionuclides behavior. On a base of conducted researches it is concluded that presence of transuranium nuclides in cuts is mainly caused by destruction of fuel particles. Size of particles is decreased because of destruction and transuranium nuclides penetrate into root-inhabited layers of soil.