Desarrollo de un proceso para la producción de 99Mo con menor generación de residuos radiactivos basados en extracción gaseosa
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Comisión Nacional de Energía Atómica. Gerencia de Área Académica. Gerencia Instituto de Tecnología Nuclear Dan Beninson
Universidad Nacional San Martin. Instituto de Tecnología Nuclear Dan Beninson
Universidad Nacional San Martin. Instituto de Tecnología Nuclear Dan Beninson
Resumen
Esta tesis se enfocó en la generación de un proceso novedoso para la producción de 99Mo, a través de la fisión nuclear de 235U o activación neutrónica del 98Mo incorporados en blancos carbonos porosos provenientes de materiales orgánicos, como fibra de sisal, mediante la sublimación de hexacarbonilo de molibdeno (Mo(CO)6). Se realizaron procesos de remoción de impurezas y funcionalización del sisal mediante tratamientos hidrotermales con diversas soluciones ácidas. A partir de ese estudio, y de manera paralela al trabajo principal de tesis, se pudo abordar el tema de adsorción de uranio en agua de mar, obteniendo buenos resultados, logrando cargar alrededor de 2,5 mgU g-1 de sisal funcionalizado con ácido amino trimetil fosfónico (ATMP). Posteriormente, se realizaron estudios de adsorción de molibdeno y uranio en sisal tratado hidrotermalmente (TH) antes y después de la pirolización (THP), logrando mejores resultados en la adsorción previa a la pirólisis. Se realizaron todos los estudios de caracterización micro y macro estructural en cada muestra. Se observaron valores de área superficial altos, alrededor de los 1600 m2 g -1 para el sisal cargada con uranio y pirolizada a 750°C. Se realizaron estudios de sublimación, mediante un equipo de termogravimetría acoplado a un espectrómetro de masas, de Mo(CO)6 incorporado en el sisal THP a través de una mezcla mecánica, tratadas a diferentes temperaturas y con incorporación de uranio, molibdeno y algunos elementos simulantes de productos de fisión, mostrando un mayor rendimiento de sublimación en el sisal THP a 750°C, para la mayoría de los casos. Finalmente, se realizó la irradiación de dos muestras en el RA-3, la primera con Mo(CO)6 y la segunda con una mezcla de Mo(CO)6 y una fibra de carbón activado comercial llamado Kynol®. Se observó el efecto Szilard Chalmers y se cuantificó el contenido de 99Mo, mediante espectrometría gamma, en las muestras que estaban presentes en la fase orgánica (diclorometano) y en la fase acuosa (ácido clorhídrico), dando peores resultados en la muestra con contenido de Kynol®, con una retención de más del 90% de 99Mo dentro de la matriz carbonosa.
This thesis focused on the development of a novel process for the production of 99Mo through the nuclear fission of 235U or the neutron activation of 98Mo incorporated into porous carbon targets derived from organic materials such as sisal fiber, using the sublimation of molybdenum hexacarbonyl (Mo(CO)6). Impurity removal and functionalization processes were carried out on sisal through hydrothermal treatments with various acidic solutions. As a result of this study, and in parallel with the main thesis work, the topic of uranium adsorption in seawater was addressed, yielding good results, around 2,5 mgU g-1 being loaded onto sisal functionalized with aminotrimethylphosphonic acid (ATMP). Subsequently, adsorption studies of molybdenum and uranium on hydrothermally treated sisal (HT) before and after pyrolysis (HTP) were conducted, with better results achieved in the adsorption prior to pyrolysis. Comprehensive micro and macro structural characterization studies were performed on each sample. High specific surface area values were observed, reaching around 1600 m2 g-1 for sisal loaded with uranium and pyrolyzed at 750°C. Sublimation studies were carried out, using a thermogravimetry apparatus coupled with a mass spectrometer, for Mo(CO)6 incorporated into sisal HTP through mechanical mixing, treated at different temperatures, and with the incorporation of uranium, molybdenum, and some fission product simulating elements, showing a higher sublimation yield in sisal HTP at 750°C for most cases. Finally, two samples were irradiated in the RA-3 reactor, the first with Mo(CO)6 and the second with a mixture of Mo(CO)6 and a commercially available activated carbon fiber called Kynol®. The Szilard-Chalmers effect was observed, and the 99Mo content was quantified through gamma spectrometry in the samples present in the organic phase (dichloromethane) and the aqueous phase (hydrochloric acid), giving worse results in the sample with Kynol® content, with a retention of over 90% of 99Mo within the carbonaceous matrix.
This thesis focused on the development of a novel process for the production of 99Mo through the nuclear fission of 235U or the neutron activation of 98Mo incorporated into porous carbon targets derived from organic materials such as sisal fiber, using the sublimation of molybdenum hexacarbonyl (Mo(CO)6). Impurity removal and functionalization processes were carried out on sisal through hydrothermal treatments with various acidic solutions. As a result of this study, and in parallel with the main thesis work, the topic of uranium adsorption in seawater was addressed, yielding good results, around 2,5 mgU g-1 being loaded onto sisal functionalized with aminotrimethylphosphonic acid (ATMP). Subsequently, adsorption studies of molybdenum and uranium on hydrothermally treated sisal (HT) before and after pyrolysis (HTP) were conducted, with better results achieved in the adsorption prior to pyrolysis. Comprehensive micro and macro structural characterization studies were performed on each sample. High specific surface area values were observed, reaching around 1600 m2 g-1 for sisal loaded with uranium and pyrolyzed at 750°C. Sublimation studies were carried out, using a thermogravimetry apparatus coupled with a mass spectrometer, for Mo(CO)6 incorporated into sisal HTP through mechanical mixing, treated at different temperatures, and with the incorporation of uranium, molybdenum, and some fission product simulating elements, showing a higher sublimation yield in sisal HTP at 750°C for most cases. Finally, two samples were irradiated in the RA-3 reactor, the first with Mo(CO)6 and the second with a mixture of Mo(CO)6 and a commercially available activated carbon fiber called Kynol®. The Szilard-Chalmers effect was observed, and the 99Mo content was quantified through gamma spectrometry in the samples present in the organic phase (dichloromethane) and the aqueous phase (hydrochloric acid), giving worse results in the sample with Kynol® content, with a retention of over 90% of 99Mo within the carbonaceous matrix.