Publication: Modelo computacional termofluidodinámico del almacenamiento en seco de combustible nuclear
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2018-09
Defense date
2018-10-16
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Abstract
La producción de energía eléctrica ha generado una importante cantidad de residuos
radiactivos de fisión nuclear durante los últimos setenta años. Tenemos el compromiso con las
próximas generaciones de desarrollar sistemas que garanticen su almacenamiento seguro de
forma indefinida. La opción más ampliamente aceptada es el almacenamiento geológico
profundo, que la legislación española exige que vaya precedido de un almacenamiento en
seco en contenedores estancos. Garantizar la seguridad de cada diseño de contenedor, con el
fin de preservar la integridad del combustible nuclear, requiere la realización de lentos y muy
costosos experimentos. El estudio del estado del combustible puede optimizarse mediante la
validación de modelos computacionales que simulan los procesos físicos (principalmente
termofluidodinámicos) que tienen lugar en estos contenedores, contrastadas con resultados
experimentales. Hasta la fecha, estas simulaciones se han enfocado en combustibles de bajo
quemado, mientras que las líneas actuales de investigación, con el fin de hacer un mejor
aprovechamiento energético del combustible, están optando por condiciones de alto quemado,
bajo las cuales, todavía no se ha conseguido garantizar el seguro almacenaje de los residuos.
Recientemente se han publicado datos empíricos de una instalación experimental a escala
llamada “Dry Cask Simulator” (DCS) que es una réplica de un contenedor de hormigón de
alto quemado para almacenamiento en seco de combustible usado. Este hecho permite validar
nuevos modelos computacionales bajo estas nuevas condiciones de quemado.
Este Trabajo de Fin de Grado (TFG) presenta la validación entre la simulación
computacional realizada de esta instalación, mediante el software ANSYS-Fluent, y los datos
experimentales publicados. Para ello se ha empleado una novedosa aproximación en la que el
complejo diseño detallado de los elementos combustibles del contenedor se modela como si
se tratasen de un medio poroso con propiedades termofísicas equivalentes; lo cual, reduciría el
coste computacional requerido.
La comparación con los resultados experimentales del DCS, junto con las aproximaciones
realizadas, ha permitido validar exitosamente el modelo computacional para las potencias más
representativas, lo que permitirá contribuir a los análisis de seguridad de combustibles de alto
quemado y ayudar a optimizar en un futuro próximo el diseño de nuevos contenedores.
The production of electric energy has generated a significant amount of radioactive waste resulting from nuclear fission for the last seventy years. We are committed to our future generations to developing systems able to keep such waste securely stored for an indefinite time. The most widely accepted choice is the so-called deep geological repository, which the Spanish legislation demands it to be preceded by a dry storage that takes place in hermetic containers. Ensuring the safety of each container design, aiming to preserve the nuclear fuel integrity, requires the realization of slow and very expensive experiments. The study of the fuel state can be optimized by means of the validation of computational models which simulates the physical processes (mainly thermo-fluid dynamic) taking place in these containers, checked with experimental results. So far, these studies have been focused on lowburnup fuel simulations, whereas the current research trends, with the aim of making the most of the energetic resources of the fuel, are turning to high-burnup conditions, under which the safe storage of waste has not been yet guaranteed. Recently, it has been published empirical data collected from a scaled experimental facility called Dry Cask Simulator (DCS), which is a replica of a high-burnup concrete cask for the dry storage of used nuclear fuel. This fact allows to validate new computational models under these new burnup conditions. This Final Degree Project presents the validation between the computational simulation of this facility, via the ANSYS Fluent software, and the published experimental data. To do so, it has been implemented an innovative approximation technique in which the complex detailed design of the fuel elements within the container are modelled as if they were a porous media with equivalent thermophysical properties. This would reduce the required computational cost. The comparison with the experimental results from the DCS, along with the approximations that have been carried out, have made it possible to successfully validate the computational model for the most representative thermal powers, which in turn, will contribute to the safety analysis regarding high-burnup fuels and help optimize in the near future the design of new containers.
The production of electric energy has generated a significant amount of radioactive waste resulting from nuclear fission for the last seventy years. We are committed to our future generations to developing systems able to keep such waste securely stored for an indefinite time. The most widely accepted choice is the so-called deep geological repository, which the Spanish legislation demands it to be preceded by a dry storage that takes place in hermetic containers. Ensuring the safety of each container design, aiming to preserve the nuclear fuel integrity, requires the realization of slow and very expensive experiments. The study of the fuel state can be optimized by means of the validation of computational models which simulates the physical processes (mainly thermo-fluid dynamic) taking place in these containers, checked with experimental results. So far, these studies have been focused on lowburnup fuel simulations, whereas the current research trends, with the aim of making the most of the energetic resources of the fuel, are turning to high-burnup conditions, under which the safe storage of waste has not been yet guaranteed. Recently, it has been published empirical data collected from a scaled experimental facility called Dry Cask Simulator (DCS), which is a replica of a high-burnup concrete cask for the dry storage of used nuclear fuel. This fact allows to validate new computational models under these new burnup conditions. This Final Degree Project presents the validation between the computational simulation of this facility, via the ANSYS Fluent software, and the published experimental data. To do so, it has been implemented an innovative approximation technique in which the complex detailed design of the fuel elements within the container are modelled as if they were a porous media with equivalent thermophysical properties. This would reduce the required computational cost. The comparison with the experimental results from the DCS, along with the approximations that have been carried out, have made it possible to successfully validate the computational model for the most representative thermal powers, which in turn, will contribute to the safety analysis regarding high-burnup fuels and help optimize in the near future the design of new containers.
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Keywords
Ingeniería del medio ambiente, Almacenamiento geológico profundo, “Dry Cask Simulator” (DCS), Simulación