LEE- Enerji Bilim ve Teknoloji-Doktora
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ÖgeInvestigation of diffusion of redox sensitive elements in nuclear waste in polymer-based barrier systems(Graduate School, 2023-09-14) Durmuş İleri, Rüveyda Kübra ; Erentürk, Sema ; 301152005 ; Energy Science and TechnologyDespite the promotion of nuclear power due to its high capacity factor, low volume of wastes, low operation cost, and low greenhouse effect contribution, some issues, such as high radioactive wastes, continue to be a concern. Nonetheless, research into the disposal and storage of radioactive waste in waste repositories has continued. The migration of radioactive waste into the biosphere and the access of water to waste repositories are the main issues with these facilities. There is widespread agreement that waste repositories should have multiple barriers made up of geological formation and engineered barriers. Where the radionuclides first come into contact, the engineered barrier typically consists of buffer material. In this work, the composite barrier material PAN/clinoptilolite composite ion exchanger was used to describe interactions with 126Sn and 79Se adsorption behavior. This PhD thesis' findings have been presented at two conferences internationally and published in three top-notch peer-reviewed journals. The first chapter mentions the importance of nuclear, the challenges of nuclear, Turkiye's position in nuclear and problems that will arise in the future for radioactive waste issues. Being reliable, high capacity factor, solution for the concerns of climate change and environment and providing the high-technology opportunity make the nuclear power attractive. Besides these brilliant advantages, there are some concerns about nuclear power to create hesitation in public such as safety and radioactive wastes. The root reasons of these concerns and the persuasive arguments are presented. Moreover, the motivation, driven force and objectives and aims of this study are explained in this chapter. The comply with the energy strategy of Turkiye, the nucler power plants, that can vary different technologies such as SMRs are planned to serve and the amount of waste generation because of the NPPs need to manage. Therefore, the radioactive waste management should be planned in detail. The second chapter present the literature review belonging to the key concepts of this study. The position of the radioactive waste in nuclear fuel cycle, the classification and production of the radioactive wastes, applied radioactive waste management and immolization techniques in the world, disposal of the radioactive wastes, the types of the disposal and some applications of the disposal in some countries are taken into account. Furthermore, the adsorption concept tin and selenium, which are the two of the most important but rarely found in literature redox-sensitive radionuclides in the radioactive waste area are taken account. With this motivation, it is aimed to develop and characterize new barrier materials with more effective and safe barrier properties that will be an alternative to existing barrier systems and to examine the applicability of these barrier materials for the retention of 126Sn and 79Se. The third chapter is related with the used material and applied method during this study. A new polymer/clay nanocomposite material as a barrier material are synthesized and characteristic of this new barrier material are investigated in terms of thermal stability and surface analysis. Moreover, interaction between tin and selenium radionuclides in the radioactive waste area and developed barrier material are characterized by data collected with examining under different circumstances, such as variable initial concentrations, interaction times, and temperatures and using adsorption isotherms, kinetic calculations, thermodynamic parameters, kinetic models based on diffusion. Furthermore, the risk assessments because of tin and selenium from radioactive waste area are analyzed in terms of radiologicaly dose assessment for freshwater and terrestrial biotas by using the ERICA Assessment Tool, exposure in human because of accidental migration of the these radionuclides by using the GoldSim Monte Carlo Simulation Software and carcinogenic and non-carcinogenic risks and excess lifetime cancer risks. The forth chapter gives the result and discussion of the experiments and analysis mentioned above. The tin ion adsorption on the barrier material has been seen to fit into the D-R isotherm model. The thermodynamic characteristics were used to determine that the tin's adsorption onto the barrier was endothermic. The tin adsorption process was shown to be consistent with the pseudo second-order model based on the kinetic evaluation. Using GOLDSIM Monte Carlo Simulation Software, the risk of 126Sn migration as a result of an accident in the radioactive waste repository was evaluated. Tin was assessed for its excess lifetime cancer risks and its carcinogenic and non-carcinogenic risks. For selenium, it has been found as a consequence that a crucial part of the composite barrier material's effectiveness in preventing selenium transfer from the waste storage region to the biosphere is played by this. For adults, the total carcinogenic risk (TCR) values for ingestion ranged from 4.93E-17 to 4.03E-16, while for infants, they ranged from 6.30E-22 to 5.16E-21. For adults, TCR values for the dermal way vary from 5.28E-21 to 4.32E-20, whereas for infants, they range from 7.74E-31 to 6.34E- 30. The exposed total dose range of reference biota as such crustaceans, phytoplankton, and vascular plants in freshwater was calculated as 4.02E6-3.87E9 μG h-1 for 126Sn isotope, and 3.35E07-1.92E12 μG h-1 for 79Se isotope using composite barrier material. In terrestrial reference biota such as annelids, grasses and grasses, lichens, and bryophytes, mammals and trees, the exposed total dose range was calculated as 4.51E06-7.41E04 μG h-1 for 126Sn and 2.15E06-5.53E09 μG h-1 for 79Se. Thus, it was determined that the existence of barrier material significantly reduced the total exposure of freshwater and terrestrial biota. The fifth and last chapter includes the chapter mentioned key findings of all these studies.