Publication: Raman spectroscopy: a versatile tool in the multianalitycal characterisation of nuclear fuel
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2019-03-04
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Universidad Complutense de Madrid
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Abstract
La presente tesis, titulada “Espectroscopía Raman: una herramienta versátil en la caracterización multianalítica del combustible nuclear”, consiste de cuatro bloques principales. La primera parte concierne los antecedentes y la consecuente introducción al tema en discusión, enfatizando los objetivos a cumplir. La segunda parte está dedicada a la metodología seguida a lo largo de los distintos estudios incluidos, en particular en lo que se refiere al empleo de la técnica de espectroscopía Raman. Así, la tercera parte corresponde a los resultados fundamentales obtenidos y la cuarta a las conclusiones generales deducidas de ellos. La oxidación del dióxido de uranio (UO2), combustible nuclear usado en la mayoría de centrales nucleares en operación en el mundo, ha suscitado siempre gran interés. Esto es debido a los potenciales riesgos que dicho proceso podría provocar si llegara a producirse, durante su almacenamiento una vez irradiado en el reactor, la presencia de un defecto desapercibido en los elementos combustibles o un fallo de barreras de contención. Si esto ocurriera en condiciones de almacenamiento temporal en seco, como en el caso del planeado ATC español, el contacto del oxígeno atmosférico con el combustible irradiado (CI), el cual presenta una gran complejidad físico-química y alta radiotoxicidad, podría inducir a la oxidación de la matriz de UO2 hasta U3O8. Este fenómeno se ve facilitado por el efecto de la alta temperatura generada por el calor residual, proveniente del decaimiento radiactivo del CI. Dado que esta conversión a U3O8 conlleva un aumento del ~36% en volumen, podría llegar a ocurrir la pérdida de integridad (pulverización) del CI, dificultando su futura recuperación y gestión, tanto con el fin de reprocesarlo como de su acondicionamiento para un almacenamiento definitivo en formaciones geológicas...
The present thesis, entitled “Raman spectroscopy: a versatile tool in the multianalytical characterisation of nuclear fuel”, consists of four main blocks. The first part concerns the background information and the consequent introduction to the issue under discussion, emphasising the objectives to be fulfilled. The second part is devoted to the methodology followed throughout the different enclosed studies, in particular with regard to the employment of the Raman spectroscopy technique. Then, the third part corresponds to the core results obtained and the fourth one to the overall conclusions drawn from these outcomes. The oxidation of uranium dioxide (UO2), a nuclear fuel used in the majority of nuclear plants in operation across the world, has always raised great interest. This is due to the potential risks that such process might provoke in the event of the presence of any undetected defect in the fuel elements or of a complete shielding failure during its storage after being irradiated in the reactor. If this occurred under dry interim storage conditions, as in the case of the planned Spanish ATC, the contact of atmospheric oxygen with the spent nuclear fuel (SNF), which presents a large physicochemical complexity and high radiotoxicity, might induce the oxidation of the UO2matrix up to U3O8. The latter phenomenon is facilitated by the effect of the high temperature aroused from the SNF radioactive decay heat. Given that the conversion to U3O8 entails a volume increase of ~36%, SNF integrity loss (pulverisation) might take place, hindering its future retrieval and management, either with the aim of reprocessing the SNF or refurbishing it for its final disposal in geological formations.
The present thesis, entitled “Raman spectroscopy: a versatile tool in the multianalytical characterisation of nuclear fuel”, consists of four main blocks. The first part concerns the background information and the consequent introduction to the issue under discussion, emphasising the objectives to be fulfilled. The second part is devoted to the methodology followed throughout the different enclosed studies, in particular with regard to the employment of the Raman spectroscopy technique. Then, the third part corresponds to the core results obtained and the fourth one to the overall conclusions drawn from these outcomes. The oxidation of uranium dioxide (UO2), a nuclear fuel used in the majority of nuclear plants in operation across the world, has always raised great interest. This is due to the potential risks that such process might provoke in the event of the presence of any undetected defect in the fuel elements or of a complete shielding failure during its storage after being irradiated in the reactor. If this occurred under dry interim storage conditions, as in the case of the planned Spanish ATC, the contact of atmospheric oxygen with the spent nuclear fuel (SNF), which presents a large physicochemical complexity and high radiotoxicity, might induce the oxidation of the UO2matrix up to U3O8. The latter phenomenon is facilitated by the effect of the high temperature aroused from the SNF radioactive decay heat. Given that the conversion to U3O8 entails a volume increase of ~36%, SNF integrity loss (pulverisation) might take place, hindering its future retrieval and management, either with the aim of reprocessing the SNF or refurbishing it for its final disposal in geological formations.
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Tesis de la Universidad Complutense de Madrid, Facultad de Ciencias Químicas, Departamento de Química Física, leída el 25-10-2018