Modeling and experimental design to characterize permeation and gettering of hydrogen isotopes in fusion materials

The roadmap towards fusion electricity includes the construction of an experimental fusion reactor called DEMO (DEMOnstration power plant). A critical element of DEMO is the tritium breeding blanket. Amongst others, two breeding blanket designs are currently under investigation: the HCPB (helium-cooled pebble bed) and the WCLL (watercooled lithium-lead) breeding blanket. In an HCPB breeding blanket, tritium is bred in lithium-containing ceramic pebble beds rinsed by a helium purge gas flowing past helium coolant channels. In a WCLL breeding blanket, a flowing lithium-lead breeder fluid is penetrated by water coolant pipes. In both designs, it is inevitable that radioactive tritium permeates from the breeder zone through Eurofer’97 steel walls into the adjacent coolant. To ensure a safe operation of DEMO, finding methods that mitigate tritium contamination of the coolant is essential. Previous experimental observations suggest that the addition of protium to the breeder fluid or coolant of the breeding blankets might, under certain conditions, reduce the tritium permeation flux. However, there is insufficient information in the literature that would allow the evaluation of this technique as a suitable tritium mitigation method. For this purpose, in the first part of this thesis, a theoretical study of multi-isotopic hydrogen gas-to-gas (relevant to an HCPB breeding blanket) and liquid metal-to-water (relevant to a WCLL breeding blanket) co- and counter-permeation is conducted in which the cause of the permeation flux altering effect of multi-isotopic permeation is revealed. Algebraic formulas are derived that allow expressing the tritium permeation flux as a function of the concentration of simultaneously co- or counter-permeating protium. Numerical system-level hydrogen transport models of the HCPB and WCLL breeding zones are developed which allow simulation of the occurring tritium permeation fluxes for different protium concentrations in the respective breeder fluid and the coolant. According to the simulations, an addition of protium to the coolant of an HCPB breeding blanket only leads to a reduction in tritium permeation when the protium concentration is too high to be technically feasible. However, adding protium to the HCPB purge gas is found to indeed result in a significant reduction in tritium permeation flux at still relatively low protium concentrations and should therefore be considered as a tritium mitigation method for HCPB breeding blankets. It is found that an increased concentration of protium in the lithium-lead or water coolant of a WCLL breeding blanket can only lead to an increase in tritium permeation and should hence be avoided. The numerical model and derived algebraic formulas describing gas-to-gas counter-permeation are experimentally validated by reproducing experimental data. To enable additional on-site experimental verification of gas-to-gas co- and counter permeation effects with Eurofer’97 as membrane material a new experimental facility is developed from scratch, called COOPER (CO- and cOunter-permeation) experiment. This thesis presents the experimental design and commissioning of the COOPER facility as well as preliminary mono-isotopic permeation measurements in which hydrogen transport coefficients such as the diffusivity, permeability and Sieverts’ constant of deuterium in Eurofer’97 are determined. Moreover, detailed experimental procedures for performing co- and counter-permeation flux measurements with the COOPER experiment are presented. The described procedures are supported by numerical simulations of multiisotopic permeation measurements taking into account the geometry and experimental conditions of the COOPER device. Another key research facility to be built on the path to fusion power is DONES (DEMO-Oriented Neutron Source), an experimental neutron irradiation facility for fusionrelevant materials. It consists of a deuterium beam colliding with a liquid lithium target that is part of a lithium loop system. Nuclear stripping reactions occur between the deuterons and the lithium, producing neutrons, but also protium, deuterium and tritium, which accumulate in the lithium. To comply with hydrogen concentration limits in lithium, an yttrium-based hydrogen getter trap will be installed. However, the physical processes that determine the absorption dynamics and the getter capacity of such a trap have not yet been sufficiently studied to allow a reliable trap design. For this reason, the second part of this thesis is devoted to the numerical and experimental investigation of hydrogen capture in DONES with the objective of defining trap design conditions that ensure meeting DONES safety limits. A numerical tool is developed from scratch capable of simulating multi-isotopic hydrogen transport in the DONES lithium loop connected to an arbitrary yttrium pebble bed. It includes the physical mechanisms of lithium and yttrium hydride formation, which is a novelty in system-level hydrogen transport modeling. A thermodynamic analysis of the lithium-yttrium-hydrogen system is carried out which reveals the solubility of hydrogen in different yttrium hydride phases exposed to hydrogen-loaded lithium. Moreover, an approximate concentrationdependent relationship of hydrogen diffusivity in yttrium is derived and incorporated into the model. Simulations are performed to analyze the dynamics of hydrogen purification processes during different operating phases of DONES by varying design parameters of the trap. It is found that yttrium dihydride formation greatly increases the gettering capacity of the trap and prevents the concentration in the lithium to increase above a critical value. Moreover, algebraic formulas are derived that allow calculating the required yttrium pebble bed mass and trap replacement period at any given temperature to comply with DONES safety requirements. Finally, the model is validated by a numerical reproduction of experimental results. To allow future experimental validation of the developed model, a new experimental lithium system is developed and put into operation. It is called the LYDER (Lithium system for Yttrium-based DEeuterium Retention) experiment, the design and construction of which are presented in this thesis. The LYDER system is designed to allow the loading of 100mL of molten lithium with a controlled concentration of deuterium. The design foresees creating a pressure differential in two argon-filled tanks which moves the deuterium-loaded lithium through a thin pipe system connected to an yttrium-based deuterium trap. The LYDER system is equipped with a lithium sample extraction system and a thermal desorption spectroscopy branch with the purpose of analyzing the extracted samples for their deuterium content. Numerical hydrogen transport models of the developed lithium system and the deuterium injection system are created and simulation results are discussed in this thesis.El camino hacia la energía de fusión incluye la construcción de un reactor de fusión experimental denominado DEMO (DEMOnstration power plant). Un elemento crítico de DEMO es la envoltura reproductora de tritio (de ahora en adelante breeding blanket) donde se produce el combustible tritio. Entre otros, se están investigando intensamente dos diseños de breeding blankts: el HCPB (helium-cooled pebble bed) y el WCLL (watercooled lithium-lead) breding blanket. En el HCPB breeding blanket, el tritio se genera en lechos de pebbles cerámicos antes de ser arrastrado por un gas de purga de helio que fluye a lo largo de canales de refrigeración de helio. En el WCLL breeding blanket el tritio se produce en litio-plomo líquido que fluye a través de tubos refrigerados por agua. En ambos diseños, es inevitable que el tritio radiactivo generado permea desde la zona de su producción, a través de las paredes de acero de Eurofer’97, hacia el refrigerante. Para garantizar un funcionamiento seguro de DEMO, es esencial encontrar métodos que mitiguen la contaminación del refrigerante por tritio. Resultados experimentales previos sugieren que, en determinadas condiciones, la inyección de protio a la zona de producción de tritio o al refrigerante podría reducir el flujo de permeación de tritio al refrigerante. Sin embargo, hoy en día no existe suficiente información en la literatura que permita evaluar esta técnica como método de mitigación de tritio. Con este fin, en la primera parte de esta disertación se lleva a cabo un estudio teórico de la co- y contra-permeación multi-isotópica de gas-a-gas (relevante para un breeding blanket HCPB) y de metal líquido-a-agua (relevante para un breeding blanket WCLL). De esta manera se revela la causa de la alteración del flujo de permeación por efectos multi-isotópicas. Se derivan fórmulas algebraicas que permiten expresar el flujo de permeación de tritio en función de la concentración de protio que simultáneamente co- o contra-permea. Además, en esta tesis, se presenta el desarollo de modelos numéricos del transporte de hidrógeno a nivel de sistema de las zonas de producción de tritio en los breeding blankets HCPB y WCLL que permiten simular los flujos de permeación de tritio para diferentes concentraciones de protio añadido. De acuerdo con las simulaciones, la inyección de protio al refrigerante de un breeding blanket HCPB solamente resulta en una reducción de la permeación de tritio cuando la concentración de protio es demasiado alta para ser técnicamente viable. Sin embargo, se ha comprobado que la adición de protio al gas de purga del HCPB produce una reducción significativa a concentraciones de protio relativamente bajas, por lo cual se debería considerar como un posible método de mitigación de tritio, eficaz y barato. Se ha descubierto que una mayor concentración de protio en el refrigerante de litio-plomo o agua de un breeding blanket WCLL sólo puede resultar en un aumento de la permeación de tritio y, por lo tanto, debe evitarse. El modelo numérico y las fórmulas algebraicas derivadas que describen la contra-permeación gas-a-gas se validan mediante datos experimentales. Para permitir una verificación experimental adicional in situ de los efectos predichos tanto de la co-permeación gas-a-gas como de la contra-permeación gas-a-gas con Eurofer’ 97 como material de membrana, se desarrolla una nueva instalación experimental desde cero, denominada experimento COOPER (CO- and cOunter-PERmeation). Esta tesis presenta el diseño experimental y la puesta en marcha de la instalación COOPER, así como mediciones preliminares de permeación mono-isotópica en las que se determinan coeficientes de transporte de hidrógeno como la difusividad, la permeabilidad y la constante de Sievert de deuterio en Eurofer’97. Además, se presentan procedimientos experimentales detallados para realizar mediciones de flujo de co-permeación y contrapermeación con el experimento COOPER. Los procedimientos descritos están respaldados por simulaciones numéricas, teniendo en cuenta la geometría característica y las condiciones experimentales del experimento COOPER. Otra instalación de investigación clave que se construirá en el camino hacia la energía de fusión es DONES (DEMO-Oriented Neutron Source), una instalación experimental de irradiación neutrónica de materiales para la fusión. DONES consiste en un haz de deuterio que colisiona con un blanco de litio líquido que forma parte de un lazo de litio. Reacciones nucleares entre los deuterones y el litio producen neutrones, pero también protio, deuterio y tritio, que se acumulan en el litio. Para respetar los límites de concentración de isotopos de hidrógeno en el litio, se instalará una trampa captadora de hidrógeno a base de itrio. Hasta ahora, los procesos físicos que determinan la dinámica de absorción y la capacidad de captación de una trampa de este tipo no se han investigado lo suficiente como para poder diseñar una trampa fiable. Por esta razón, la segunda parte de esta tesis se dedica a la investigación numérica y experimental de los mecanismos físicos implicados con el objetivo de definir los parámetros de diseño de la trampa apropiados para DONES. Se desarrolla desde cero una herramienta numérica capaz de simular el transporte de hidrógeno que se produce en el lazo de litio de DONES conectado a un lecho de pebbles de itrio. El modelo incluye los mecanismos físicos de la formación de hidruros de litio e itrio, lo que constituye una novedad en la modelado del transporte de hidrógeno a nivel de sistema. Se lleva a cabo un análisis termodinámico del sistema litio-itrio-hidrógeno que revela la solubilidad de los isótopos de hidrógeno en diferentes fases de hidruro de itrio expuesto a litio cargado de hidrógeno. Además, se deriva una relación aproximada de la difusividad de hidrógeno en itrio dependiente de la concentración de hidrógeno que está incorporado en el modelo. Se realizan simulaciones para analizar la dinámica de los procesos de purificación de isótopos de hidrógeno durante diferentes fases de operación de DONES variando los parámetros de diseño de la trampa. Se observa que la formación de dihidruro de itrio aumenta en gran medida la capacidad de absorción de la trampa y evita que la concentración en el litio aumente por encima de un valor crítico. Además, se derivan fórmulas algebraicas que permiten calcular la masa necesaria del lecho de pebbles de itrio y el periodo de sustitución de la trampa para cumplir los requisitos de seguridad de DONES. El modelo se valida mediante una reproducción numérica de resultados experimentales. Para facilitar la futura validación experimental del modelo creado, se ha desarrollado y puesto en funcionamiento un nuevo sistema experimental de litio en el marco de esta tesis. Se trata del experimento LYDER (Lithium system for Yttrium-based DEeuterium Retention), cuyo diseño y construcción se presentan en esta tesis. El sistema LYDER está diseñado para permitir la carga de 100mL de litio fundido con una concentración controlada de deuterio. El diseño prevé la creación de un diferencial de presión entre dos tanques presurizados con argón que mueve el litio cargado de deuterio a través de una linea de tuberías que pasa por una trampa experimental de deuterio. El sistema LYDER está equipado con un sistema de extracción de muestras de litio y una rama de espectroscopia de desorción térmica con el objetivo de analizar las muestras extraídas para determinar su contenido de deuterio. Además, se presentan modelos numéricos del transporte de deuterio en el sistema de litio y del sistema de inyección de deuterio de LYDER. Los resultados de las simulaciones están analizados en esta disertación.Programa de Doctorado en Ciencia e Ingeniería de Materiales por la Universidad Carlos III de MadridPresidente: Ángel Ibarra Sánchez.- Secretario: Manuel José Pérez Mendoza.- Vocal: Igor Peñalva Bengo

The state of the Martian climate

60°N was +2.0°C, relative to the 1981–2010 average value (Fig. 5.1). This marks a new high for the record. The average annual surface air temperature (SAT) anomaly for 2016 for land stations north of starting in 1900, and is a significant increase over the previous highest value of +1.2°C, which was observed in 2007, 2011, and 2015. Average global annual temperatures also showed record values in 2015 and 2016. Currently, the Arctic is warming at more than twice the rate of lower latitudes

Mechanical design of the optical modules intended for IceCube-Gen2

IceCube-Gen2 is an expansion of the IceCube neutrino observatory at the South Pole that aims to increase the sensitivity to high-energy neutrinos by an order of magnitude. To this end, about 10,000 new optical modules will be installed, instrumenting a fiducial volume of about 8 km3. Two newly developed optical module types increase IceCube’s current sensitivity per module by a factor of three by integrating 16 and 18 newly developed four-inch PMTs in specially designed 12.5-inch diameter pressure vessels. Both designs use conical silicone gel pads to optically couple the PMTs to the pressure vessel to increase photon collection efficiency. The outside portion of gel pads are pre-cast onto each PMT prior to integration, while the interiors are filled and cast after the PMT assemblies are installed in the pressure vessel via a pushing mechanism. This paper presents both the mechanical design, as well as the performance of prototype modules at high pressure (70 MPa) and low temperature (−40∘C), characteristic of the environment inside the South Pole ice

The next generation neutrino telescope: IceCube-Gen2

The IceCube Neutrino Observatory, a cubic-kilometer-scale neutrino detector at the geographic South Pole, has reached a number of milestones in the field of neutrino astrophysics: the discovery of a high-energy astrophysical neutrino flux, the temporal and directional correlation of neutrinos with a flaring blazar, and a steady emission of neutrinos from the direction of an active galaxy of a Seyfert II type and the Milky Way. The next generation neutrino telescope, IceCube-Gen2, currently under development, will consist of three essential components: an array of about 10,000 optical sensors, embedded within approximately 8 cubic kilometers of ice, for detecting neutrinos with energies of TeV and above, with a sensitivity five times greater than that of IceCube; a surface array with scintillation panels and radio antennas targeting air showers; and buried radio antennas distributed over an area of more than 400 square kilometers to significantly enhance the sensitivity of detecting neutrino sources beyond EeV. This contribution describes the design and status of IceCube-Gen2 and discusses the expected sensitivity from the simulations of the optical, surface, and radio components

Sensitivity of IceCube-Gen2 to measure flavor composition of Astrophysical neutrinos

The observation of an astrophysical neutrino flux in IceCube and its detection capability to separate between the different neutrino flavors has led IceCube to constraint the flavor content of this flux. IceCube-Gen2 is the planned extension of the current IceCube detector, which will be about 8 times larger than the current instrumented volume. In this work, we study the sensitivity of IceCube-Gen2 to the astrophysical neutrino flavor composition and investigate its tau neutrino identification capabilities. We apply the IceCube analysis on a simulated IceCube-Gen2 dataset that mimics the High Energy Starting Event (HESE) classification. Reconstructions are performed using sensors that have 3 times higher quantum efficiency and isotropic angular acceptance compared to the current IceCube optical modules. We present the projected sensitivity for 10 years of data on constraining the flavor ratio of the astrophysical neutrino flux at Earth by IceCube-Gen2

Deep Learning Based Event Reconstruction for the IceCube-Gen2 Radio Detector

The planned in-ice radio array of IceCube-Gen2 at the South Pole will provide unprecedented sensitivity to ultra-high-energy (UHE) neutrinos in the EeV range. The ability of the detector to measure the neutrino’s energy and direction is of crucial importance. This contribution presents an end-to-end reconstruction of both of these quantities for both detector components of the hybrid radio array (\u27shallow\u27 and \u27deep\u27) using deep neural networks (DNNs). We are able to predict the neutrino\u27s direction and energy precisely for all event topologies, including the electron neutrino charged-current (νe-CC) interactions, which are more complex due to the LPM effect. This highlights the advantages of DNNs for modeling the complex correlations in radio detector data, thereby enabling a measurement of the neutrino energy and direction. We discuss how we can use normalizing flows to predict the PDF for each individual event which allows modeling the complex non-Gaussian uncertainty contours of the reconstructed neutrino direction. Finally, we discuss how this work can be used to further optimize the detector layout to improve its reconstruction performance