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 global impact of the transport sectors on the atmospheric aerosol and the resulting climate effects under the Shared Socioeconomic Pathways (SSPs)

A global aerosol–climate model is applied to quantify the impact of the transport sectors (land transport, shipping, and aviation) on aerosol and climate. Global simulations are performed for the present day (2015), based on the emission inventory of the Climate Model Intercomparison Project Phase 6 (CMIP6), and for near-term (2030) and mid-term (2050) future projections, under the Shared Socioeconomic Pathways (SSPs). The results for the present day show that land transport emissions have a large impact on near-surface concentrations of black carbon and aerosol nitrate over the most populated areas of the globe, but with contrasting patterns in terms of relative contributions between developed and developing countries. In spite of the recently introduced regulations to limit the fuel sulfur content in the shipping sector, shipping emissions are still responsible for a considerable impact on aerosol sulfate near-surface concentrations, about 0.5 to 1 µg m−3 in the most travelled regions, with significant effects on continental air pollution and in the northern polar regions as well. Aviation impacts on aerosol mass are found to be quite small, of the order of a few nanograms per cubic metre, while this sector considerably affects particle number concentrations, contributing up to 20 %–30 % of the upper-tropospheric particle number concentration at the northern mid-latitudes. The transport-induced impacts on aerosol mass and number concentrations result in a present-day radiative forcing of −164, −145, and −64 mW m−2 for land transport, shipping, and aviation, respectively, with a dominating contribution by aerosol–cloud interactions. These forcings represent a marked offset to the CO2 warming from the transport sectors and are therefore very relevant for climate policy. The projections under the SSPs show that the impact of the transport sectors on aerosol and climate are generally consistent with the narratives underlying these scenarios: the lowest impacts of transport on both aerosol and climate are simulated under SSP1, especially for the land transport sector, while SSP3 is generally characterized by the largest effects. Notable exceptions to this picture, however, exist, as the emissions of other anthropogenic sectors also contribute to the overall aerosol concentrations and thus modulate the relevance of the transport sectors in the different scenarios, not always consistently with their underlying storyline. On a qualitative level, the results for the present day mostly confirm the findings of our previous assessment for the year 2000, which used a predecessor version of the same model and the CMIP5 emission data. Some important quantitative differences are found, which can mostly be ascribed to the improved representation of aerosol background concentrations in the present study.</p

Dust ice nuclei effects on cirrus clouds

In order to study aerosol–cloud interactions in cirrus clouds, we apply a new multiple-mode ice microphysical scheme to the general circulation model ECHAM5-HAM. The multiple-mode ice microphysical scheme allows for analysis of the competition between homogeneous freezing of solution droplets, deposition nucleation of pure dust particles, and immersion freezing of coated dust particles and pre-existing ice. We base the freezing efficiencies of coated and pure dust particles on the most recent laboratory data. The effect of pre-existing ice, which has been neglected in previous ice nucleation parameterizations, is to deplete water vapour by depositional growth and thus prevent homogeneous and heterogeneous freezing from occurring

Exploring the uncertainties in the aviation soot-cirrus effect

A global aerosol–climate model, including a twomoment cloud microphysical scheme and a parametrization for aerosol-induced ice formation in cirrus clouds, is applied in order to quantify the impact of aviation soot on natural cirrus clouds. Several sensitivity experiments are performed to assess the uncertainties in this effect related to (i) the assumptions on the ice nucleation abilities of aviation soot, (ii) the representation of vertical updrafts in the model, and (iii) the use of reanalysis data to relax the model dynamics (the socalled nudging technique)

A global climatology of ice-nucleating particles under cirrus conditions derived from model simulations with MADE3 in EMAC

Ice-nucleating particles (INPs) have important influences on cirrus clouds and the climate system; however, their global atmospheric distribution in the cirrus regime is still very uncertain. We present a global climatology of INPs under cirrus conditions derived from model simulations, considering the mineral dust, soot, crystalline ammonium sulfate, and glassy organics INP types. The comparison of respective INP concentrations indicates the large importance of ammonium sulfate particles

An aerosol classification scheme for global simulations using the K-means machine learning method

The K-means machine learning algorithm is applied to climatological data of seven aerosol properties from a global aerosol simulation using EMAC-MADE3. The aim is to partition the aerosol properties across the global atmosphere in specific aerosol regimes; this is done mainly for evaluation purposes. K-means is an unsupervised machine learning method with the advantage that an a priori definition of the aerosol classes is not required. Using K-means, we are able to quantitatively define global aerosol regimes, so-called aerosol clusters, and explain their internal properties and their location and extension. This analysis shows that aerosol regimes in the lower troposphere are strongly influenced by emissions. Key drivers of the clusters' internal properties and spatial distribution are, for instance, pollutants from biomass burning and biogenic sources, mineral dust, anthropogenic pollution, and corresponding mixtures. Several continental clusters propagate into oceanic regions as a result of long-range transport of air masses. The identified oceanic regimes show a higher degree of pollution in the Northern Hemisphere than over the southern oceans. With increasing altitude, the aerosol regimes propagate from emission-induced clusters in the lower troposphere to roughly zonally distributed regimes in the middle troposphere and in the tropopause region. Notably, three polluted clusters identified over Africa, India, and eastern China cover the whole atmospheric column from the lower troposphere to the tropopause region. The results of this analysis need to be interpreted taking the limitations and strengths of global aerosol models into consideration. On the one hand, global aerosol simulations cannot estimate small-scale and localized processes due to the coarse resolution. On the other hand, they capture the spatial pattern of aerosol properties on the global scale, implying that the clustering results could provide useful insights for aerosol research. To estimate the uncertainties inherent in the applied clustering method, two sensitivity tests have been conducted (i) to investigate how various data scaling procedures could affect the K-means classification and (ii) to compare K-means with another unsupervised classification algorithm (HAC, i.e. hierarchical agglomerative clustering). The results show that the standardization based on sample mean and standard deviation is the most appropriate standardization method for this study, as it keeps the underlying distribution of the raw data set and retains the information of outliers. The two clustering algorithms provide similar classification results, supporting the robustness of our conclusions. The classification procedures presented in this study have a markedly wide application potential for future model-based aerosol studies

The formation of mutated IgM memory B cells in rat splenic marginal zones is an antigen dependent process

Previous studies in rodents have indicated that only a minor fraction of the immunoglobulin heavy chain variable region (IGHV-Cμ) transcripts carry somatic mutations and are considered memory B cells. This is in marked contrast to humans where nearly all marginal zone B (MZ-B) cells are mutated. Here we show in rats that the proportion of mutated IgM+ MZ-B cells varies significantly between the various IGHV genes analyzed, ranging from 27% mutated IGHV5 transcripts to 65% mutated IGHV4 transcripts. The observed data on mutated sequences in clonally-related B cells with a MZ-B cell or follicular B (FO-B) cell phenotype indicates that mutated IgM+ MZ-B and FO-B cells have a common origin. To further investigate the origin of mutated IgM+ MZ-B cells we determined whether mutations occurred in rearranged IGHV-Cμ transcripts using IGHV4 and IGHV5 genes from neonatal rat MZ-B cells and FO-B cells. We were not able to detect mutations in any of the IGHV4 and IGHV5 genes expressed by MZ-B cells or FO-B cells obtained from neonatal rat spleens. Germinal centres (GCs) are absent from neonatal rat spleen in the first few weeks of their life, and no mutations were found in any of the neonatal sequences, not even in the IGHV4 gene family which accumulates the highest number of mutated sequences (66%) in the adult rat. Therefore, these data do not support the notion that MZ-B cells in rats mutate their IGHV genes as part of their developmental program, but are consistent with the notion that mutated rat MZ-B cells require GCs for their generation. Our findings support that the splenic MZ of rats harbors a significant number of memory type IgM+ MZ-B cells with mutated IGHV genes and propose that these memory MZ-B cells are probably generated as a result of an antigen driven immune response in GCs, which still remains to be proven

Evaluation of the performance of four chemical transport models in predicting the aerosol chemical composition in Europe in 2005

© Author(s) 2016.Four regional chemistry transport models were applied to simulate the concentration and composition of particulate matter (PM) in Europe for 2005 with horizontal resolution 20 km. The modelled concentrations were compared with the measurements of PM chemical composition by the European Monitoring and Evaluation Programme (EMEP) monitoring network. All models systematically underestimated PM10 and PM2:5 by 10–60 %, depending on the model and the season of the year, when the calculated dry PM mass was compared with the measurements. The average water content at laboratory conditions was estimated between 5 and 20% for PM2:5 and between 10 and 25% for PM10. For majority of the PM chemical components, the relative underestimation was smaller than it was for total PM, exceptions being the carbonaceous particles and mineral dust. Some species, such as sea salt and NO3, were overpredicted by the models. There were notable differences between the models’ predictions of the seasonal variations of PM, mainly attributable to different treatments or omission of some source categories and aerosol processes. Benzo(a)pyrene concentrations were overestimated by all the models over the whole year. The study stresses the importance of improving the models’ skill in simulating mineral dust and carbonaceous compounds, necessity for high-quality emissions from wildland fires, as well as the need for an explicit consideration of aerosol water content in model–measurement comparison.Peer reviewedFinal Published versio

Modelling mineral dust emissions and atmospheric dispersion with MADE3 in EMAC v2.54

It was hypothesized that using mineral dust emission climatologies in global chemistry climate models (GCCMs), i.e. prescribed monthly-mean dust emissions representative of a specific year, may lead to misrepresentations of strong dust burst events. This could result in a negative bias of model dust concentrations compared to observations for these episodes. Here, we apply the aerosol microphysics submodel MADE3 (Modal Aerosol Dynamics model for Europe, adapted for global applications, third generation) as part of the ECHAM/MESSy Atmospheric Chemistry (EMAC) general circulation model. We employ two different representations of mineral dust emissions for our model simulations: (i) a prescribed monthly-mean climatology of dust emissions representative of the year 2000 and (ii) an online dust parametrization which calculates wind-driven mineral dust emissions at every model time step. We evaluate model results for these two dust representations by comparison with observations of aerosol optical depth from ground-based station data. The model results show a better agreement with the observations for strong dust burst events when using the online dust representation compared to the prescribed dust emissions setup. Furthermore, we analyse the effect of increasing the vertical and horizontal model resolution on the mineral dust properties in our model. We compare results from simulations with T42L31 and T63L31 model resolution (2.8∘×2.8∘ and 1.9∘×1.9∘ in latitude and longitude, respectively; 31 vertical levels) with the reference setup (T42L19). The different model versions are evaluated against airborne in situ measurements performed during the SALTRACE mineral dust campaign (Saharan Aerosol Long-range Transport and Aerosol-Cloud Interaction Experiment, June–July 2013), i.e. observations of dust transported from the Sahara to the Caribbean. Results show that an increased horizontal and vertical model resolution is able to better represent the spatial distribution of airborne mineral dust, especially in the upper troposphere (above 400 hPa). Additionally, we analyse the effect of varying assumptions for the size distribution of emitted dust but find only a weak sensitivity concerning these changes. The results of this study will help to identify the model setup best suited for future studies and to further improve the representation of mineral dust particles in EMAC-MADE3