Atık saklama alanlarında sezyumun geçirgen reaktif bariyer (GRB) sistemi ile arıtımının incelenmesi

Bu tez çalışmasında; bir nükleer kaza sonrası ve/veya atık işleme sahalarındaki faaliyetler sonucu radyonüklitlerle kontamine olmuş yüzey ve yeraltı sularının iyileştirilmesi sorununa bir çözüm oluşturulması için ham haldeki doğal malzemeler kullanılarak zeolit ve sepiyolitten oluşan iki komponentli geçirgen reaktif bariyer (GRB) sistemi geliştirilmesi önerilmiştir. Reaktif malzeme olarak seçilen ham haldeki Zeolit ve sepiyolit'in fiziksel ve kimyasal karakterizasyonları XRD, SEM-EDS, pXRF, BET, TGA, civali porozimetre, zeta potansiyeli analizleri ile yapılmıştır. Tez çalışması kapsamında arıtılmak üzere hedef radyonüklit olarak radyosezyum belirlenmiş, bu amaçla kararlı sezyum bileşiği İTÜ TRIGA MARK II Eğitim ve Araştırma Reaktörü'nde ışınlanmış ve oluşan Cs-134 radyoizotopuyla hazırlanan çözelti denemelerde kullanılmıştır. Zeolit ve sepiyolit reaktif malzemeler kullanılarak kesikli sistemde olmak üzere sulu çözeltide Cs-134 adsorpsiyonunu etkileyen çözelti pH'ı, başlangıç Cs-134 konsantrasyonu, çalkalama süresi ve sıcaklık gibi parametreler incelenmiş ve optimum alım koşulları saptanmıştır. Elde edilen sonuçlar; birim reaktif malzeme başına adsorplanan radyosezyum miktarı (mg/g), dağılma katsayısı (Kd, mL/g) ve adsorpsiyon verimi (%) parametreleri ile değerlendirilmiştir. Radyosezyumun reaktif malzemeler üzerine adsorpsiyonu için, adsorpsiyon entalpisi (ΔH°), serbest enerji değişimi (ΔG°) ve entropi değişimi (ΔS°) gibi termodinamik parametreleri hesaplanmış, her iki reaktif malzeme için de adsorpsiyon prosesinin fiziksel ve ekzotermik karakterde olduğu, düşük sıcaklıklarda kendiliğinden gerçekleştiği bulunmuştur. Kesikli sistemde sulu çözeltiden adsorplanan sezyum için elde edilen deneysel verilere Langmuir, Freundlich ve Dubinin-Radushkevich (D-R) izotermleri uygulanmıştır. Sürekli sistemde denemelerinde; sabit yatak yüksekliğindeki zeolit ve sepiyolit reaktif malzemelerle hazırlanmış kolonlarda, Cs-134 konsantrasyonu ve akış hızı parametrelerinin kırılma eğrileri üzerine etkisi araştırılmıştır. Geoteknik analizler kapsamında reaktif malzemelerin endeks özellikleri, Atterberg kıvam limitleri ve konsolidasyon özellikleri belirlenmiştir. Endeks özellikleri hidrometri analizi ile tanımlanmıştır. Reaktif malzemelerin konsolidasyon ve geçirgenlik analizleri düşen seviyeli permeabilite tipi geçirgenlik deneyine göre uyarlanmış bir ödometre hücresinde tek boyutlu konsolidasyon ve düşen seviyeli permeabilite deneyleri gerçekleştirilmiştir. Yapılan deneysel çalışmalardan elde edilen verilerden reaktif malzemelerin permeabilite değerleri hesaplanmıştır. Geoteknik analizler, kesikli ve sürekli sistem ile elde edilen verilerden yola çıkarak iki farklı konfigürasyonda iki boyutlu ölçek GRB tasarlanmıştır. İlk uygulama Cs-134 çözeltisi ile, ikinci uygulama ise sıvı radyoaktif atık çözeltisi ile denenmiştir. İki boyutlu ölçek uygulamalarda, GRB sistemi öncesi ve sonrası radyosezyum ve diğer radyonüklitlerin aktivite konsantrasyonları belirlenmiştir. GRB sisteminin arıtım performansı, radyosezyum ve diğer radyonüklitlerin insan dışı biyotada oluşturabileceği radyolojik risk, "Environmental Risk from Ionising Contaminants: Assessment and Management (ERICA)" isimli araç ile değerlendirilmiştir. Radyosezyum ile kirlenmiş bir atık sahasında, doktora tez çalışması kapsamında önerilen GRB sisteminin kullanımı ile insan dışı organizmalar üzerinde radyolojik riskin güvenle ihmal edilebilir seviyede (10 µGy/saat) olduğu ispatlamıştır.In this thesis, the development of a two-component permeable reactive barrier system (GRB), which uses natural materials in their raw form and consists of zeolite and sepiolite, is proposed as a treatment technology for surface and underground water that was contaminated by radionuclides because of a nuclear accident and/or activity in waste treatment sites. Raw zeolite and sepiolite are chosen as reactive materials, and their physical and chemical characterizations are carried out through XRD, SEM-EDS, pXRF, BET, TGA, mercury porosimetry, zeta potential analyzes. The present study takes radiocesium as its the target radionuclide to be purified, and the solution prepared with the Cs-134 radioisotope that formed by irradiation of cesium compound in ITU TRIGA MARK II Training and Research Reactor was used in the experiments. In the batch system, the parameters of solution pH, initial Cs-134 concentration, contact time and temperature were investigated using zeolite and sepiolite as reactive materials in aqueous solutions and optimum conditions. In this regard, the optimum conditions for the adsorption process were determined. The obtained results were evaluated with the following parameters: the amount of sorption capacity (mg/g), distribution coefficient (Kd, mL/g) and percent adsorption (%). For the adsorption of radiocesium onto reactive materials, the thermodynamic parameters including the change in the free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) were calculated to describe thermodynamic behavior. It was determined that the adsorption process for both reactive materials was a spontaneous process for low temperatures, exothermic and physical in nature. The isotherm models of Langmuir, Freundlich and Dubinin-Radushkevich (D-R) were applied to describe the experimental data obtained for cesium adsorbed from aqueous solution in the batch system. The experiments of the continuous system were carried out in the fixed bed column systems, which were prepared by zeolite and sepiolite reactive materials. The effects Cs-134 concentration and flow rate parameters on the breakthrough curves were investigated. In the geotechnical analysis of reactive materials; index properties, Atterberg limits and consolidation properties were determined. The index properties of the reactive materials were specified using hydrometer analysis. The one-dimensional vertical consolidation analysis was performed by using front loading conventional loading frame for the consolidation characteristic and permeability analysis of reactive materials. Permeability values of reactive materials were calculated from the data obtained from experimental studies. Two different two-dimensional bench-scale PRB configurations were designed based on the batch, continuous system and geotechnical experiments. The first bench-scale PRB system configuration was tested with radiocesium solution, the second configuration also with liquid radioactive waste. In the bench scale tests, activity concentrations of radiosesium and other radionuclides before and after in the PRB system were determined. The treatment performance of the PRB system was evaluated with the "Environmental Risk from Ionising Contaminants: Assessment and Management (ERICA)" assessment tool, based on the radiological risk that radiocesium and other radionuclides can have on non-human biota. The assessment results proved that the radiological risk on non-human organisms is safely negligible (10 µGy/hour) with the use of the PRB system proposed within the scope of this doctoral dissertation in a waste site contaminated with radiocesium

Magnesium oxide nanoparticles: Preparation, characterization, and uranium sorption properties

WOS: 000310261600006The objective of this work was to study the sorption of uranium (VI) ions on magnesium oxide (MgO) from aqueous solutions. The MgO has been prepared via hydroxide precipitation followed by thermal decomposition of the hydroxide. MgO was characterized by X-ray powder diffraction, scanning electron microscope, and multipoint Brunauer, Emmett, and Teller. The relative importance of test parameters such concentration of adsorbate, pH, contact time, and temperature on adsorption performance of MgO for U(VI) ion were studied and the optimum sorption efficiency was found as 87.61 +/- 3.10%. Desorption tests were also carried out and desorption efficiency was found as 100% with NH4Cl and NaNO3 solutions containing 0.1 M on a single step. Typical sorption isotherms (Freundlich and Dubinin-Raduskevich) were determined for the mechanism of sorption process and thermodynamic constants (?H degrees, ?S degrees, and ?G degrees) were calculated as -8.738 kJ mol-1, -21.68 kJ mol-1, and 0.102 kJ mol-1 K-1, respectively. (C) 2011 American Institute of Chemical Engineers Environ Prog, 2011Unit of the Scientific Research Projects of Ege UniversityEge UniversityThe authors are grateful for the financial support of the Unit of the Scientific Research Projects of Ege University

Spatial distribution and risk assessment of radioactivity and heavy metal levels of sediment, surface water and fish samples from Lake Van, Turkey

WOS: 000335673800004In this study, radioactivity levels of 228 lake water samples, 63 upper and depth sediment samples and 12 fish samples from Lake Van were investigated from 2005 to 2008 and the distribution patterns of the radionuclides were presented. Analysis included gross alpha-beta and total radium isotopes activities and uranium concentrations of the water, and gross alpha and gross beta activities and relevant U-238, Th-232 and K-40 activity of the sediment and fish samples of the lake. Mean gross alpha, gross beta and radium isotopes activities of lake water were found 0.74 +/- A 0.46, 0.02 +/- A 0.01 and 0.06 +/- A 0.04 Bq/L, respectively. Mean gross alpha and beta activities in upper and depth sediments were found to be 41 +/- A 6 and 1,514 +/- A 74 Bq/kg; 77 +/- A 5 and 394 +/- A 24 Bq/kg at a 95 % confidence level, respectively. Mean activities of U-238, Th-232 and K-40 activity concentrations in upper and depth sediments were determined to be 225 +/- A 22, 70 +/- A 7 and 486 +/- A 39 Bq/kg; 174 +/- A 4, 63 +/- A 3 and 263 +/- A 25 Bq/kg, respectively. The mean gross alpha and beta, U-238, Th-232 and K-40 aktivities in fish samples were established as 47 +/- A 18, 470 +/- A 12, 0.57 +/- A 0.220, 0.022 +/- A 0.006, 319 +/- A 11 Bq/kg, respectively. The transfer factor from lake water to fish tissues, annual intake by humans consuming fish, and annual committed effective doses were estimated and evaluated.TUBITAK (The Scientific Technological Research Council of Turkey)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [104Y072]This research project work was financially supported by the TUBITAK (The Scientific Technological Research Council of Turkey) by Project Number 104Y072