Liquid lead and Lithium. A Comprehensive molecular dynamics study

Pb17Li is today a reference breeder material in diverse fusion R&D programs worldwide. One of the main issues in these programs is the problem of liquid metals breeder blanket behavior. Structural material of the blanket should meet high requirements because of extreme operating conditions. Therefore the knowledge of eutectic properties like optimal composition, physical and thermodynamic behavior or diffusion coefficients of Tritium are extremely necessary for current designs. In particular, the knowledge of the function linking the tritium concentration dissolved in liquid materials with the tritium partial pressure at a liquid/gas interface in equilibrium, CT=f(PT), is of basic importance because it directly impacts all functional properties of a blanket determining: tritium inventory, tritium permeation rate and tritium extraction efficiency. Nowadays, understanding the structure and behavior of this compound is a real goal in fusion engineering and materials science. Simulations of liquids can provide much information to the community; not only supplementing experimental data, but providing new tests of theories and ideas, making specific predictions that require experimental tests, and ultimately helping to lead to the deeper understanding and better predictive behavior.

New simulations to qualify eutectic lithium-lead as breeder material

Pb17Li is today a reference breeder material in diverse fusion R&D programs worldwide. One of the main issues is the problem of liquid metals breeder blanket behavior. The knowledge of eutectic properties like optimal composition, physical and thermodynamic behavior or diffusion coefficients of Tritium are extremely necessary for current designs. In particular, the knowledge of the function linking the tritium concentration dissolved in liquid materials with the tritium partial pressure at a liquid/gas interface in equilibrium, CT =f(PT ), is of basic importance because it directly impacts all functional properties of a blanket determining: tritium inventory, tritium permeation rate and tritium extraction efficiency. Nowadays, understanding the structure and behavior of this compound is a real goal in fusion engineering and materials science. Atomistic simulations of liquids can provide much information; not only supplementing experimental data, but providing new tests of theories and ideas, making specific predictions that require experimental tests, and ultimately helping to a deeper understanding

An eco-friendly way to fire retardant flexible polyurethane foam: layer-by-layer assembly of fully bio-based substances

The objective of the present study is to develop fully renewable and environmentally benign techniques for improving the fire safety of flexible polyurethane foams (PUFs). A multilayered coating made from cationic chitosan (CS) and anionic alginate (AL) was deposited on PUFs through layer-by-layer assembly. This coating system exhibits a slight influence on the thermal stability of PUF, but significantly improves the char formation during combustion. Cone calorimetry reveals that 10 CS-AL bilayers (only 5.7% of the foams weight) lead to a 66% and 11% reduction in peak heat release rate and total heat release, respectively, compared with those of the uncoated control. The notable decreased fire hazards of PUF are attributed to the CS-AL coatings being beneficial to form an insulating protective layer on the surface of burning materials that inhibits the oxygen and heat permeation and slows down the flammable gases in the vapor phase, and thereby improves the flame resistance. This water-based, environmentally benign natural coating will stimulate further efforts in improving fire safety for a variety of polymer substrates.

Corrosión inducida por contaminantes hidrosolubles en la intercara metal/pintura

El objetivo principal de este trabajo es profundizar en el conocimiento del fenómeno de la corrosión subpelicular inducida por contaminantes hidrosolubles en la intercara metal/pintura. La contaminación salina del substrato es una situación común en la práctica: la superficie metálica suele estar expuesta a atmósferas contaminadas antes de ser recubierta, limpieza previa del metal con abrasivos contaminados, etc. La eliminación total de estos contaminantes resulta muy difícil de conseguir incluso con las técnicas más sofisticadas de limpieza. Esta investigación se centra en la determinación del efecto de la naturaleza del contaminante y la naturaleza y espesor del recubrimiento en el proceso de corrosión subpelicular del acero. En la investigación se utilizaron dos barnices de naturaleza diferente: poliuretano y vinílico; y se aplicaron a tres espesores diferentes. Los contaminantes empleados en este trabajo fueron: NaCl, NH4C1, CaCl2, Na2S04, (NH4)2S04, NaN03, NH4N03, Ca(N03)2. Los ensayos se realizaron en una cámara de condensación de humedad permanente. Los tiempos de exposición fueron 100, 300 y 600 horas. La velocidad de corrosión se evaluó gravimétricamente, mediante la técnica de pérdida de peso. Se realizaron estudios de permeabilidad al oxígeno y al agua de películas libres de substrato, evaluación de la velocidad de corrosión de probetas sin pintar inmersas en soluciones salinas de los contaminantes seleccionados, conductividad de dichas soluciones salinas, solubilidad del oxígeno en las soluciones salinas, adherencia en seco y en húmedo a diferentes tiempos de exposición. Se aporta evidencia respecto al control ejercido en el proceso corrosivo por el oxígeno que permea a través de la película, mientras que la permeación de agua controla la pérdida de adherencia del recubrimiento. Ambas permeabilidades dependen de la naturaleza del recubrimiento y de su espesor. Se ha investigado la influencia de la naturaleza del contaminante en la intercara metal/pintura. La naturaleza del catión parece quedar enmascarada por el efecto definitivo del anión. La concentración salina ejerce asimismo un efecto importante en la corrosión subpelicular. ABSTRACT The main aim of this work is to study in depth the knowledge of underfilm corrosión induced by hydrosoluble contaminants at the metal/paint Ínterface. The saline contamination of the substrate is a common situation in practice: metallic surfaces use to be exposed to polluted atmospheres, previous cleaning of the metal with contaminated abrasives, etc. Total elimination of these contaminants is hard to obtain even with modern cleaning techniques. This research is focused in determining the effect of contaminant nature, coating nature and its thickness on the steel underfilm corrosión process. In this work we used two varnishes with different nature: polyurethane and vinyl; they were applied in three different thicknesses. The saline contaminants employed were: NaCl, NH4C1, CaCl2, Na2S04, (NH4)2S04, NaN03, NH4N03/ Ca(N03)2. The tests were carried out in a condensation humidity chamber. The period of exposure were 100, 300 and 600 hours. Corrosión rate was assessed by weight loss. Simultaneously, studies on oxygen and water permeability of free films, assessing on corrosión rate of uncoated samples immersed in saline solutions of the selected contaminants, conductivity of these solutions, oxygen solubility in saline solutions, wet and dry adhesión of the polyurethane varnish at different periods of exposure, were carried out. There is clear evidence about control on corrosión process of oxygen that passes through the coating, while the passing of water controls the loss of adhesión of the coating. Both, water and oxygen permeation, depend on the nature and thickness of the coating. It has been researched the inf luence of the nature of contaminant at the metal/paint interface. The nature of the catión seems to be "masked" by the definitive effect of the nature of anión. The saline concentration also exerts an important effect on underfilm corrosión.

Diseño de un módulo de IFMIF para irradiación de envolturas regeneradoras basadas en metales líquidos para reactores de fusión

La fusión nuclear es, hoy en día, una alternativa energética a la que la comunidad internacional dedica mucho esfuerzo. El objetivo es el de generar entre diez y cincuenta veces más energía que la que consume mediante reacciones de fusión que se producirán en una mezcla de deuterio (D) y tritio (T) en forma de plasma a doscientos millones de grados centígrados. En los futuros reactores nucleares de fusión será necesario producir el tritio utilizado como combustible en el propio reactor termonuclear. Este hecho supone dar un paso más que las actuales máquinas experimentales dedicadas fundamentalmente al estudio de la física del plasma. Así pues, el tritio, en un reactor de fusión, se produce en sus envolturas regeneradoras cuya misión fundamental es la de blindaje neutrónico, producir y recuperar tritio (fuel para la reacción DT del plasma) y por último convertir la energía de los neutrones en calor. Existen diferentes conceptos de envolturas que pueden ser sólidas o líquidas. Las primeras se basan en cerámicas de litio (Li2O, Li4SiO4, Li2TiO3, Li2ZrO3) y multiplicadores neutrónicos de Be, necesarios para conseguir la cantidad adecuada de tritio. Los segundos se basan en el uso de metales líquidos o sales fundidas (Li, LiPb, FLIBE, FLINABE) con multiplicadores neutrónicos de Be o el propio Pb en el caso de LiPb. Los materiales estructurales pasan por aceros ferrítico-martensíticos de baja activación, aleaciones de vanadio o incluso SiCf/SiC. Cada uno de los diferentes conceptos de envoltura tendrá una problemática asociada que se estudiará en el reactor experimental ITER (del inglés, “International Thermonuclear Experimental Reactor”). Sin embargo, ITER no puede responder las cuestiones asociadas al daño de materiales y el efecto de la radiación neutrónica en las diferentes funciones de las envolturas regeneradoras. Como referencia, la primera pared de un reactor de fusión de 4000MW recibiría 30 dpa/año (valores para Fe-56) mientras que en ITER se conseguirían <10 dpa en toda su vida útil. Esta tesis se encuadra en el acuerdo bilateral entre Europa y Japón denominado “Broader Approach Agreement “(BA) (2007-2017) en el cual España juega un papel destacable. Estos proyectos, complementarios con ITER, son el acelerador para pruebas de materiales IFMIF (del inglés, “International Fusion Materials Irradiation Facility”) y el dispositivo de fusión JT-60SA. Así, los efectos de la irradiación de materiales en materiales candidatos para reactores de fusión se estudiarán en IFMIF. El objetivo de esta tesis es el diseño de un módulo de IFMIF para irradiación de envolturas regeneradoras basadas en metales líquidos para reactores de fusión. El módulo se llamará LBVM (del inglés, “Liquid Breeder Validation Module”). La propuesta surge de la necesidad de irradiar materiales funcionales para envolturas regeneradoras líquidas para reactores de fusión debido a que el diseño conceptual de IFMIF no contaba con esta utilidad. Con objeto de analizar la viabilidad de la presente propuesta, se han realizado cálculos neutrónicos para evaluar la idoneidad de llevar a cabo experimentos relacionados con envolturas líquidas en IFMIF. Así, se han considerado diferentes candidatos a materiales funcionales de envolturas regeneradoras: Fe (base de los materiales estructurales), SiC (material candidato para los FCI´s (del inglés, “Flow Channel Inserts”) en una envoltura regeneradora líquida, SiO2 (candidato para recubrimientos antipermeación), CaO (candidato para recubrimientos aislantes), Al2O3 (candidato para recubrimientos antipermeación y aislantes) y AlN (material candidato para recubrimientos aislantes). En cada uno de estos materiales se han calculado los parámetros de irradiación más significativos (dpa, H/dpa y He/dpa) en diferentes posiciones de IFMIF. Estos valores se han comparado con los esperados en la primera pared y en la zona regeneradora de tritio de un reactor de fusión. Para ello se ha elegido un reactor tipo HCLL (del inglés, “Helium Cooled Lithium Lead”) por tratarse de uno de los más prometedores. Además, los valores también se han comparado con los que se obtendrían en un reactor rápido de fisión puesto que la mayoría de las irradiaciones actuales se hacen en reactores de este tipo. Como conclusión al análisis de viabilidad, se puede decir que los materiales funcionales para mantos regeneradores líquidos podrían probarse en la zona de medio flujo de IFMIF donde se obtendrían ratios de H/dpa y He/dpa muy parecidos a los esperados en las zonas más irradiadas de un reactor de fusión. Además, con el objetivo de ajustar todavía más los valores, se propone el uso de un moderador de W (a considerar en algunas campañas de irradiación solamente debido a que su uso hace que los valores de dpa totales disminuyan). Los valores obtenidos para un reactor de fisión refuerzan la idea de la necesidad del LBVM, ya que los valores obtenidos de H/dpa y He/dpa son muy inferiores a los esperados en fusión y, por lo tanto, no representativos. Una vez demostrada la idoneidad de IFMIF para irradiar envolturas regeneradoras líquidas, y del estudio de la problemática asociada a las envolturas líquidas, también incluida en esta tesis, se proponen tres tipos de experimentos diferentes como base de diseño del LBVM. Éstos se orientan en las necesidades de un reactor tipo HCLL aunque a lo largo de la tesis se discute la aplicabilidad para otros reactores e incluso se proponen experimentos adicionales. Así, la capacidad experimental del módulo estaría centrada en el estudio del comportamiento de litio plomo, permeación de tritio, corrosión y compatibilidad de materiales. Para cada uno de los experimentos se propone un esquema experimental, se definen las condiciones necesarias en el módulo y la instrumentación requerida para controlar y diagnosticar las cápsulas experimentales. Para llevar a cabo los experimentos propuestos se propone el LBVM, ubicado en la zona de medio flujo de IFMIF, en su celda caliente, y con capacidad para 16 cápsulas experimentales. Cada cápsula (24-22 mm de diámetro y 80 mm de altura) contendrá la aleación eutéctica LiPb (hasta 50 mm de la altura de la cápsula) en contacto con diferentes muestras de materiales. Ésta irá soportada en el interior de tubos de acero por los que circulará un gas de purga (He), necesario para arrastrar el tritio generado en el eutéctico y permeado a través de las paredes de las cápsulas (continuamente, durante irradiación). Estos tubos, a su vez, se instalarán en una carcasa también de acero que proporcionará soporte y refrigeración tanto a los tubos como a sus cápsulas experimentales interiores. El módulo, en su conjunto, permitirá la extracción de las señales experimentales y el gas de purga. Así, a través de la estación de medida de tritio y el sistema de control, se obtendrán los datos experimentales para su análisis y extracción de conclusiones experimentales. Además del análisis de datos experimentales, algunas de estas señales tendrán una función de seguridad y por tanto jugarán un papel primordial en la operación del módulo. Para el correcto funcionamiento de las cápsulas y poder controlar su temperatura, cada cápsula se equipará con un calentador eléctrico y por tanto el módulo requerirá también ser conectado a la alimentación eléctrica. El diseño del módulo y su lógica de operación se describe en detalle en esta tesis. La justificación técnica de cada una de las partes que componen el módulo se ha realizado con soporte de cálculos de transporte de tritio, termohidráulicos y mecánicos. Una de las principales conclusiones de los cálculos de transporte de tritio es que es perfectamente viable medir el tritio permeado en las cápsulas mediante cámaras de ionización y contadores proporcionales comerciales, con sensibilidades en el orden de 10-9 Bq/m3. Los resultados son aplicables a todos los experimentos, incluso si son cápsulas a bajas temperaturas o si llevan recubrimientos antipermeación. Desde un punto de vista de seguridad, el conocimiento de la cantidad de tritio que está siendo transportada con el gas de purga puede ser usado para detectar de ciertos problemas que puedan estar sucediendo en el módulo como por ejemplo, la rotura de una cápsula. Además, es necesario conocer el balance de tritio de la instalación. Las pérdidas esperadas el refrigerante y la celda caliente de IFMIF se pueden considerar despreciables para condiciones normales de funcionamiento. Los cálculos termohidráulicos se han realizado con el objetivo de optimizar el diseño de las cápsulas experimentales y el LBVM de manera que se pueda cumplir el principal requisito del módulo que es llevar a cabo los experimentos a temperaturas comprendidas entre 300-550ºC. Para ello, se ha dimensionado la refrigeración necesaria del módulo y evaluado la geometría de las cápsulas, tubos experimentales y la zona experimental del contenedor. Como consecuencia de los análisis realizados, se han elegido cápsulas y tubos cilíndricos instalados en compartimentos cilíndricos debido a su buen comportamiento mecánico (las tensiones debidas a la presión de los fluidos se ven reducidas significativamente con una geometría cilíndrica en lugar de prismática) y térmico (uniformidad de temperatura en las paredes de los tubos y cápsulas). Se han obtenido campos de presión, temperatura y velocidad en diferentes zonas críticas del módulo concluyendo que la presente propuesta es factible. Cabe destacar que el uso de códigos fluidodinámicos (e.g. ANSYS-CFX, utilizado en esta tesis) para el diseño de cápsulas experimentales de IFMIF no es directo. La razón de ello es que los modelos de turbulencia tienden a subestimar la temperatura de pared en mini canales de helio sometidos a altos flujos de calor debido al cambio de las propiedades del fluido cerca de la pared. Los diferentes modelos de turbulencia presentes en dicho código han tenido que ser estudiados con detalle y validados con resultados experimentales. El modelo SST (del inglés, “Shear Stress Transport Model”) para turbulencia en transición ha sido identificado como adecuado para simular el comportamiento del helio de refrigeración y la temperatura en las paredes de las cápsulas experimentales. Con la geometría propuesta y los valores principales de refrigeración y purga definidos, se ha analizado el comportamiento mecánico de cada uno de los tubos experimentales que contendrá el módulo. Los resultados de tensiones obtenidos, han sido comparados con los valores máximos recomendados en códigos de diseño estructural como el SDC-IC (del inglés, “Structural Design Criteria for ITER Components”) para así evaluar el grado de protección contra el colapso plástico. La conclusión del estudio muestra que la propuesta es mecánicamente robusta. El LBVM implica el uso de metales líquidos y la generación de tritio además del riesgo asociado a la activación neutrónica. Por ello, se han estudiado los riesgos asociados al uso de metales líquidos y el tritio. Además, se ha incluido una evaluación preliminar de los riesgos radiológicos asociados a la activación de materiales y el calor residual en el módulo después de la irradiación así como un escenario de pérdida de refrigerante. Los riesgos asociados al módulo de naturaleza convencional están asociados al manejo de metales líquidos cuyas reacciones con aire o agua se asocian con emisión de aerosoles y probabilidad de fuego. De entre los riesgos nucleares destacan la generación de gases radiactivos como el tritio u otros radioisótopos volátiles como el Po-210. No se espera que el módulo suponga un impacto medioambiental asociado a posibles escapes. Sin embargo, es necesario un manejo adecuado tanto de las cápsulas experimentales como del módulo contenedor así como de las líneas de purga durante operación. Después de un día de después de la parada, tras un año de irradiación, tendremos una dosis de contacto de 7000 Sv/h en la zona experimental del contenedor, 2300 Sv/h en la cápsula y 25 Sv/h en el LiPb. El uso por lo tanto de manipulación remota está previsto para el manejo del módulo irradiado. Por último, en esta tesis se ha estudiado también las posibilidades existentes para la fabricación del módulo. De entre las técnicas propuestas, destacan la electroerosión, soldaduras por haz de electrones o por soldadura láser. Las bases para el diseño final del LBVM han sido pues establecidas en el marco de este trabajo y han sido incluidas en el diseño intermedio de IFMIF, que será desarrollado en el futuro, como parte del diseño final de la instalación IFMIF. ABSTRACT Nuclear fusion is, today, an alternative energy source to which the international community devotes a great effort. The goal is to generate 10 to 50 times more energy than the input power by means of fusion reactions that occur in deuterium (D) and tritium (T) plasma at two hundred million degrees Celsius. In the future commercial reactors it will be necessary to breed the tritium used as fuel in situ, by the reactor itself. This constitutes a step further from current experimental machines dedicated mainly to the study of the plasma physics. Therefore, tritium, in fusion reactors, will be produced in the so-called breeder blankets whose primary mission is to provide neutron shielding, produce and recover tritium and convert the neutron energy into heat. There are different concepts of breeding blankets that can be separated into two main categories: solids or liquids. The former are based on ceramics containing lithium as Li2O , Li4SiO4 , Li2TiO3 , Li2ZrO3 and Be, used as a neutron multiplier, required to achieve the required amount of tritium. The liquid concepts are based on molten salts or liquid metals as pure Li, LiPb, FLIBE or FLINABE. These blankets use, as neutron multipliers, Be or Pb (in the case of the concepts based on LiPb). Proposed structural materials comprise various options, always with low activation characteristics, as low activation ferritic-martensitic steels, vanadium alloys or even SiCf/SiC. Each concept of breeding blanket has specific challenges that will be studied in the experimental reactor ITER (International Thermonuclear Experimental Reactor). However, ITER cannot answer questions associated to material damage and the effect of neutron radiation in the different breeding blankets functions and performance. As a reference, the first wall of a fusion reactor of 4000 MW will receive about 30 dpa / year (values for Fe-56) , while values expected in ITER would be <10 dpa in its entire lifetime. Consequently, the irradiation effects on candidate materials for fusion reactors will be studied in IFMIF (International Fusion Material Irradiation Facility). This thesis fits in the framework of the bilateral agreement among Europe and Japan which is called “Broader Approach Agreement “(BA) (2007-2017) where Spain plays a key role. These projects, complementary to ITER, are mainly IFMIF and the fusion facility JT-60SA. The purpose of this thesis is the design of an irradiation module to test candidate materials for breeding blankets in IFMIF, the so-called Liquid Breeder Validation Module (LBVM). This proposal is born from the fact that this option was not considered in the conceptual design of the facility. As a first step, in order to study the feasibility of this proposal, neutronic calculations have been performed to estimate irradiation parameters in different materials foreseen for liquid breeding blankets. Various functional materials were considered: Fe (base of structural materials), SiC (candidate material for flow channel inserts, SiO2 (candidate for antipermeation coatings), CaO (candidate for insulating coatings), Al2O3 (candidate for antipermeation and insulating coatings) and AlN (candidate for insulation coating material). For each material, the most significant irradiation parameters have been calculated (dpa, H/dpa and He/dpa) in different positions of IFMIF. These values were compared to those expected in the first wall and breeding zone of a fusion reactor. For this exercise, a HCLL (Helium Cooled Lithium Lead) type was selected as it is one of the most promising options. In addition, estimated values were also compared with those obtained in a fast fission reactor since most of existing irradiations have been made in these installations. The main conclusion of this study is that the medium flux area of IFMIF offers a good irradiation environment to irradiate functional materials for liquid breeding blankets. The obtained ratios of H/dpa and He/dpa are very similar to those expected in the most irradiated areas of a fusion reactor. Moreover, with the aim of bringing the values further close, the use of a W moderator is proposed to be used only in some experimental campaigns (as obviously, the total amount of dpa decreases). The values of ratios obtained for a fission reactor, much lower than in a fusion reactor, reinforce the need of LBVM for IFMIF. Having demonstrated the suitability of IFMIF to irradiate functional materials for liquid breeding blankets, and an analysis of the main problems associated to each type of liquid breeding blanket, also presented in this thesis, three different experiments are proposed as basis for the design of the LBVM. These experiments are dedicated to the needs of a blanket HCLL type although the applicability of the module for other blankets is also discussed. Therefore, the experimental capability of the module is focused on the study of the behavior of the eutectic alloy LiPb, tritium permeation, corrosion and material compatibility. For each of the experiments proposed an experimental scheme is given explaining the different module conditions and defining the required instrumentation to control and monitor the experimental capsules. In order to carry out the proposed experiments, the LBVM is proposed, located in the medium flux area of the IFMIF hot cell, with capability of up to 16 experimental capsules. Each capsule (24-22 mm of diameter, 80 mm high) will contain the eutectic allow LiPb (up to 50 mm of capsule high) in contact with different material specimens. They will be supported inside rigs or steel pipes. Helium will be used as purge gas, to sweep the tritium generated in the eutectic and permeated through the capsule walls (continuously, during irradiation). These tubes, will be installed in a steel container providing support and cooling for the tubes and hence the inner experimental capsules. The experimental data will consist of on line monitoring signals and the analysis of purge gas by the tritium measurement station. In addition to the experimental signals, the module will produce signals having a safety function and therefore playing a major role in the operation of the module. For an adequate operation of the capsules and to control its temperature, each capsule will be equipped with an electrical heater so the module will to be connected to an electrical power supply. The technical justification behind the dimensioning of each of these parts forming the module is presented supported by tritium transport calculations, thermalhydraulic and structural analysis. One of the main conclusions of the tritium transport calculations is that the measure of the permeated tritium is perfectly achievable by commercial ionization chambers and proportional counters with sensitivity of 10-9 Bq/m3. The results are applicable to all experiments, even to low temperature capsules or to the ones using antipermeation coatings. From a safety point of view, the knowledge of the amount of tritium being swept by the purge gas is a clear indicator of certain problems that may be occurring in the module such a capsule rupture. In addition, the tritium balance in the installation should be known. Losses of purge gas permeated into the refrigerant and the hot cell itself through the container have been assessed concluding that they are negligible for normal operation. Thermal hydraulic calculations were performed in order to optimize the design of experimental capsules and LBVM to fulfill one of the main requirements of the module: to perform experiments at uniform temperatures between 300-550ºC. The necessary cooling of the module and the geometry of the capsules, rigs and testing area of the container were dimensioned. As a result of the analyses, cylindrical capsules and rigs in cylindrical compartments were selected because of their good mechanical behavior (stresses due to fluid pressure are reduced significantly with a cylindrical shape rather than prismatic) and thermal (temperature uniformity in the walls of the tubes and capsules). Fields of pressure, temperature and velocity in different critical areas of the module were obtained concluding that the proposal is feasible. It is important to mention that the use of fluid dynamic codes as ANSYS-CFX (used in this thesis) for designing experimental capsules for IFMIF is not direct. The reason for this is that, under strongly heated helium mini channels, turbulence models tend to underestimate the wall temperature because of the change of helium properties near the wall. Therefore, the different code turbulence models had to be studied in detail and validated against experimental results. ANSYS-CFX SST (Shear Stress Transport Model) for transitional turbulence model has been identified among many others as the suitable one for modeling the cooling helium and the temperature on the walls of experimental capsules. Once the geometry and the main purge and cooling parameters have been defined, the mechanical behavior of each experimental tube or rig including capsules is analyzed. Resulting stresses are compared with the maximum values recommended by applicable structural design codes such as the SDC- IC (Structural Design Criteria for ITER Components) in order to assess the degree of protection against plastic collapse. The conclusion shows that the proposal is mechanically robust. The LBVM involves the use of liquid metals, tritium and the risk associated with neutron activation. The risks related with the handling of liquid metals and tritium are studied in this thesis. In addition, the radiological risks associated with the activation of materials in the module and the residual heat after irradiation are evaluated, including a scenario of loss of coolant. Among the identified conventional risks associated with the module highlights the handling of liquid metals which reactions with water or air are accompanied by the emission of aerosols and fire probability. Regarding the nuclear risks, the generation of radioactive gases such as tritium or volatile radioisotopes such as Po-210 is the main hazard to be considered. An environmental impact associated to possible releases is not expected. Nevertheless, an appropriate handling of capsules, experimental tubes, and container including purge lines is required. After one day after shutdown and one year of irradiation, the experimental area of the module will present a contact dose rate of about 7000 Sv/h, 2300 Sv/h in the experimental capsules and 25 Sv/h in the LiPb. Therefore, the use of remote handling is envisaged for the irradiated module. Finally, the different possibilities for the module manufacturing have been studied. Among the proposed techniques highlights the electro discharge machining, brazing, electron beam welding or laser welding. The bases for the final design of the LBVM have been included in the framework of the this work and included in the intermediate design report of IFMIF which will be developed in future, as part of the IFMIF facility final design.

Binary metal oxides for composite ultrafiltration membranes

A new ultrafiltration membrane was developed by the incorporation of binary metal oxides inside polyethersulfone. Physico-chemical characterization of the binary metal oxides demonstrated that the presence of Ti in the TiO2?ZrO2 system results in an increase of the size of the oxides, and also their dispersity. The crystalline phases of the synthesized binary metal oxides were identified as srilankite and zirconium titanium oxide. The effect of the addition of ZrO2 can be expressed in terms of the inhibition of crystal growth of anocrystalline TiO2 during the synthesis process. For photocatalytic applications the band gap of the synthesized semiconductors was determined, confirming a gradual increase (blue shift) in the band gap as the amount of Zr loading increases. Distinct distributions of binary metal oxides were found along the permeation axis for the synthesized membranes. Particles with Ti are more uniformly dispersed throughout the membrane cross-section. The physico-chemical characterization of membranes showed a strong correlation between some key membrane properties and the spatial particle distribution in the membrane structure. The proximity of metal oxide fillers to the membrane surface determines the hydrophilicity and porosity of modified membranes. Membranes incorporating binary metal oxides were found to be promising candidates for wastewater treatment by ultrafiltration, considering the observed improvement influx and anti-fouling properties of doped membranes. Multi-run fouling tests of doped membranes confirmed the stability of permeation through membranes embedded with binary TiO2?ZrO2 particles.

Choroid plexus epithelial expression of MDR1 P glycoprotein and multidrug resistance-associated protein contribute to the blood–cerebrospinal-fluid drug-permeability barrier

The blood–brain barrier and a blood–cerebrospinal-fluid (CSF) barrier function together to isolate the brain from circulating drugs, toxins, and xenobiotics. The blood–CSF drug-permeability barrier is localized to the epithelium of the choroid plexus (CP). However, the molecular mechanisms regulating drug permeability across the CP epithelium are defined poorly. Herein, we describe a drug-permeability barrier in human and rodent CP mediated by epithelial-specific expression of the MDR1 (multidrug resistance) P glycoprotein (Pgp) and the multidrug resistance-associated protein (MRP). Noninvasive single-photon-emission computed tomography with 99mTc-sestamibi, a membrane-permeant radiopharmaceutical whose transport is mediated by both Pgp and MRP, shows a large blood-to-CSF concentration gradient across intact CP epithelium in humans in vivo. In rats, pharmacokinetic analysis with 99mTc-sestamibi determined the concentration gradient to be greater than 100-fold. In membrane fractions of isolated native CP from rat, mouse, and human, the 170-kDa Pgp and 190-kDa MRP are identified readily. Furthermore, the murine proteins are absent in CP isolated from their respective mdr1a/1b(−/−) and mrp(−/−) gene knockout littermates. As determined by immunohistochemical and drug-transport analysis of native CP and polarized epithelial cell cultures derived from neonatal rat CP, Pgp localizes subapically, conferring an apical-to-basal transepithelial permeation barrier to radiolabeled drugs. Conversely, MRP localizes basolaterally, conferring an opposing basal-to-apical drug-permeation barrier. Together, these transporters may coordinate secretion and reabsorption of natural product substrates and therapeutic drugs, including chemotherapeutic agents, antipsychotics, and HIV protease inhibitors, into and out of the central nervous system.

Deltorphin transport across the blood–brain barrier

In vivo antinociception studies demonstrate that deltorphins are opioid peptides with an unusually high blood–brain barrier penetration rate. In vitro, isolated bovine brain microvessels can take up deltorphins through a saturable nonconcentrative permeation system, which is apparently distinct from previously described systems involved in the transport of neutral amino acids or of enkephalins. Removing Na+ ions from the incubation medium decreases the carrier affinity for deltorphins (−25%), but does not affect the Vmax value of the transport. The nonselective opiate antagonist naloxone inhibits deltorphin uptake by brain microvessels, but neither the selective δ-opioid antagonist naltrindole nor a number of opioid peptides with different affinities for δ- or μ-opioid receptors compete with deltorphins for the transport. Binding studies demonstrate that μ-, δ-, and κ-opioid receptors are undetectable in the microvessel preparation. Preloading of the microvessels with l-glutamine results in a transient stimulation of deltorphin uptake. Glutamine-accelerated deltorphin uptake correlates to the rate of glutamine efflux from the microvessels and is abolished by naloxone.

Patch-clamp and amperometric recordings from norepinephrine transporters: Channel activity and voltage-dependent uptake

Transporters for the biogenic amines dopamine, norepinephrine, epinephrine and serotonin are largely responsible for transmitter inactivation after release. They also serve as high-affinity targets for a number of clinically relevant psychoactive agents, including antidepressants, cocaine, and amphetamines. Despite their prominent role in neurotransmitter inactivation and drug responses, we lack a clear understanding of the permeation pathway or regulation mechanisms at the single transporter level. The resolution of radiotracer-based flux techniques limits the opportunities to dissect these problems. Here we combine patch-clamp recording techniques with microamperometry to record the transporter-mediated flux of norepinephrine across isolated membrane patches. These data reveal voltage-dependent norepinephrine flux that correlates temporally with antidepressant-sensitive transporter currents in the same patch. Furthermore, we resolve unitary flux events linked with bursts of transporter channel openings. These findings indicate that norepinephrine transporters are capable of transporting neurotransmitter across the membrane in discrete shots containing hundreds of molecules. Amperometry is used widely to study neurotransmitter distribution and kinetics in the nervous system and to detect transmitter release during vesicular exocytosis. Of interest regarding the present application is the use of amperometry on inside-out patches with synchronous recording of flux and current. Thus, our results further demonstrate a powerful method to assess transporter function and regulation.

Transmembrane topology of a CLC chloride channel

CLC chloride channels form a large and conserved gene family unrelated to other channel proteins. Knowledge of the transmembrane topology of these channels is important for understanding the effects of mutations found in human myotonia and inherited hypercalciuric kidney stone diseases and for the interpretation of structure–function studies. We now systematically study the topology of human ClC-1, a prototype CLC channel that is defective in human myotonia. Using a combination of in vitro glycosylation scanning and protease protection assays, we show that both N and C termini face the cytoplasm and demonstrate the presence of 10 (or less likely 12) transmembrane spans. Difficult regions were additionally tested by inserting cysteines and probing the effect of cysteine-modifying reagents on ClC-1 currents. The results show that D3 crosses the membrane and D4 does not, and that L549 between D11 and D12 is accessible from the outside. Further, since the modification of cysteines introduced between D11 and D12 and at the extracellular end of D3 strongly affect ClC-1 currents, these regions are suggested to be important for ion permeation.

Permeant ion regulation of N-methyl-d-aspartate receptor channel block by Mg2+

Block of the channel of N-methyl-d-aspartate (NMDA) receptors by external Mg2+ (Mgo2+) has broad implications for the many physiological and pathological processes that depend on NMDA receptor activation. An essential property of channel block by Mgo2+ is its powerful voltage dependence. A widely cited explanation for the strength of the voltage dependence of block is that the Mgo2+-binding site is located deep in the channel of NMDA receptors; Mgo2+ then would sense most of the membrane potential field during block. However, recent electrophysiological and mutagenesis studies suggest that the blocking site cannot be deep enough to account for the voltage dependence of Mgo2+ block. Here we describe the basis for this discrepancy: the magnitude and voltage dependence of channel block by Mgo2+ are strongly regulated by external and internal permeant monovalent cations. Our data support a model in which access to the channel by Mgo2+ is prevented when permeant ion-binding sites at the external entrance to the channel are occupied. Mgo2+ can block the channel only when the permeant ion-binding sites are unoccupied and then can either unblock back to the external solution or permeate the channel. Unblock to the external solution is prevented if external permeant ions bind while Mg2+ blocks the channel, although permeation is still permitted. The model provides an explanation for the strength of the voltage dependence of Mgo2+ block and quantifies the interdependence of permanent and blocking ion binding to NMDA receptors.

Rapid polyether cleavage via extracellular one-electron oxidation by a brown-rot basidiomycete

Fungi that cause brown rot of wood are essential biomass recyclers and also the principal agents of decay in wooden structures, but the extracellular mechanisms by which they degrade lignocellulose remain unknown. To test the hypothesis that brown-rot fungi use extracellular free radical oxidants as biodegradative tools, Gloeophyllum trabeum was examined for its ability to depolymerize an environmentally recalcitrant polyether, poly(ethylene oxide) (PEO), that cannot penetrate cell membranes. Analyses of degraded PEOs by gel permeation chromatography showed that the fungus cleaved PEO rapidly by an endo route. 13C NMR analyses of unlabeled and perdeuterated PEOs recovered from G. trabeum cultures showed that a major route for depolymerization was oxidative C—C bond cleavage, a reaction diagnostic for hydrogen abstraction from a PEO methylene group by a radical oxidant. Fenton reagent (Fe(II)/H2O2) oxidized PEO by the same route in vitro and therefore might account for PEO biodegradation if it is produced by the fungus, but the data do not rule out involvement of less reactive radicals. The reactivity and extrahyphal location of this PEO-degrading system suggest that its natural function is to participate in the brown rot of wood and that it may enable brown-rot fungi to degrade recalcitrant organopollutants.

Competitive regulation of CaT-like-mediated Ca2+ entry by protein kinase C and calmodulin

A finely tuned Ca2+ signaling system is essential for cells to transduce extracellular stimuli, to regulate growth, and to differentiate. We have recently cloned CaT-like (CaT-L), a highly selective Ca2+ channel closely related to the epithelial calcium channels (ECaC) and the calcium transport protein CaT1. CaT-L is expressed in selected exocrine tissues, and its expression also strikingly correlates with the malignancy of prostate cancer. The expression pattern and selective Ca2+ permeation properties suggest an important function in Ca2+ uptake and a role in tumor progression, but not much is known about the regulation of this subfamily of ion channels. We now demonstrate a biochemical and functional mechanism by which cells can control CaT-L activity. CaT-L is regulated by means of a unique calmodulin binding site, which, at the same time, is a target for protein kinase C-dependent phosphorylation. We show that Ca2+-dependent calmodulin binding to CaT-L, which facilitates channel inactivation, can be counteracted by protein kinase C-mediated phosphorylation of the calmodulin binding site.

Changes in voltage activation, Cs+ sensitivity, and ion permeability in H5 mutants of the plant K+ channel KAT1.

KAT1 is a voltage-dependent inward rectifying K+ channel cloned from the higher plant Arabidopsis thaliana [Anderson, J. A., Huprikar, S. S., Kochian, L. V., Lucas, W. J. & Gaber, R. F. (1992) Proc. Natl. Acad. Sci. USA 89, 3736-3740]. It is related to the Shaker superfamily of K+ channels characterized by six transmembrane spanning domains (S1-S6) and a putative pore-forming region between S5 and S6 (H5). The 115 region between Pro-247 and Pro-271 in KAT1 contains 14 additional amino acids when compared with Shaker [Aldrich, R. W. (1993) Nature (London) 362, 107-108]. We studied various point mutations introduced into H5 to determine whether voltage-dependent plant and animal K+ channels share similar pore structures. Through heterologous expression in Xenopus oocytes and voltage-clamp analysis combined with phenotypic analysis involving a potassium transport-defective Saccharomyces cerevisiae strain, we investigated the selectivity filter of the mutants and their susceptibility toward inhibition by cesium and calcium ions. With respect to electrophysiological properties, KAT1 mutants segregated into three groups: (i) wild-type-like channels, (ii) channels modified in selectivity and Cs+ or Ca2+ sensitivity, and (iii) a group that was additionally affected in its voltage dependence. Despite the additional 14 amino acids in H5, this motif in KAT1 is also involved in the formation of the ion-conducting pore because amino acid substitutions at Leu-251, Thr-256, Thr-259, and Thr-260 resulted in functional channels with modified ionic selectivity and inhibition. Creation of Ca2+ sensitivity and an increased susceptibility to Cs+ block through mutations within the narrow pore might indicate that both blockers move deeply into the channel. Furthermore, mutations close to the rim of the pore affecting the half-activation potential (U1/2) indicate that amino acids within the pore either interact with the voltage sensor or ion permeation feeds back on gating.

Correlation between kinetics and RNA splicing of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptors in neocortical neurons.

In the cortex fast excitatory synaptic currents onto excitatory pyramidal neurons and inhibitory nonpyramidal neurons are mediated by alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors exhibiting cell-type-specific differences in their kinetic properties. AMPA receptors consist of four subunits (GluR1-4), each existing as two splice variants, flip and flop, which critically affect the desensitization properties of receptors expressed in heterologous systems. Using single cell reverse transcription PCR to analyze the mRNA of AMPA receptor subunits expressed in layers I-III neocortical neurons, we find that 90% of the GluR1-4 in nonpyramidal neurons are flop variants, whereas 92% of the GluR1-4 in pyramidal neurons are flip variants. We also find that nonpyramidal neurons predominantly express GluR1 mRNA (GluR1/GluR1-4 = 59%), whereas pyramidal neurons contain mainly GluR2 mRNA (GluR2/GluR1-4 = 59%). However, the neuron-type-specific splicing is exhibited by all four AMPA receptor subunits. We suggest that the predominance of the flop variants contributes to the faster and more extensive desensitization in nonpyramidal neurons, compared to pyramidal cells where flip variants are dominant. Alternative splicing of AMPA receptors may play an important role in regulating synaptic function in a cell-type-specific manner, without changing permeation properties.