Análisis de patologías expansivas manifestadas en soleras tras el recalce de la cimentación en la iglesia de San Andrés (Calatayud)

Las patologías constructivas relacionadas con fenómenos expansivos en el sustrato de apoyo de edificaciones son bien conocidas, siendo la etringita el mineral responsable de dichos procesos y existiendo estrategias para su minimización, principalmente el uso de cementos sulfato resistentes. No obstante y a pesar del uso de dichas formulaciones, se ha observado que existen patologías asociadas a fenómenos expansivos en los cuales es la taumasita el mineral responsable. El potencial expansivo de este minerales tres veces mayor que el de la taumasita, por lo que su posible aparición debe ser prevista y analizada en detalle. En este trabajo se presentan los resultados del estudio de patologías por expansividad manifestadas tras la actuación de recalce por micropilotaje en la Iglesia de San Andrés (Calatayud), donde, tras su ejecución, se comenzaron a manifestar levantamientos centimétricos de las soleras en las zonas no sometidas a cargas verticales bajo la torre. El estudio detallado del fenómeno, principalmente desde el punto de vista del contenido mineralógico de los distintos niveles del subsuelo en las zonas afectadas, ha permitido identificar el origen del proceso (expansividad por formación de sales sulfatadas, relacionada con la operación de recalce estructural previa). También se han analizado las especiales condiciones que han concurrido en este caso y en las cuales, a pesar de emplear para el recalce un cemento sulfato resistente para así evitar la formación de etringita, la presencia de cal en el subsuelo ha dado lugar a la cristalización de taumasita, mineral que ha sido el responsable del fenómeno expansivo posterior a la intervención. El conocimiento de las condiciones de manifestación de este proceso servirá para adoptar precauciones en los proyectos de restauración monumental que impliquen la utilización de hormigones y morteros con cemento portland, así como para impulsar las investigaciones encaminadas a diseñar dosificaciones de cementos que permitan su minimización.Consejo General de la Arquitectura Técnica de Españ

Thaumasite identification at the restoration materials of the San Andrés church of Calatayud (Zaragoza, Spain). Mineral formation conditions and sampling preparation

El estudio realizado en el subsuelo de la capilla bautismal de la Iglesia de San Andrés (Calatayud) ha permitido comprobar que las deformaciones convexas observadas en la solera tras su restauración se han debido a la formación de taumasita. La cristalización de esta sal compleja necesita del aporte de carbonatos, sulfatos, silicatos y calcio, en un ambiente de elevada humedad y a temperaturas por debajo de 15 ºC. Todos estos factores han dado lugar a la formación de esta sal, con el consiguiente deterioro de los morteros de restauración y la manifestación del fenómeno expansivo en un plazo de unos dos años tras la intervención. La identificación de taumasita se ha llevado a cabo mediante difractometría de rayos X y microscopía electrónica de barrido, sobre muestras desecadas al aire y a temperatura ambiente. Se ha comprobado además que el secado previo de las muestras en estufa a 80 ºC interfiere en la determinación mineralógica de taumasita, haciéndola desaparecer prácticamente por completo por transformación en otras sales más simples. La presencia de taumasita en los morteros de restauración aquí empleados, elaborados con cementos resistentes a los sulfatos, confirma la importancia del control previo de las condiciones ambientales y constructivas de los materiales a emplear en actuaciones de restauración monumentalThis study, achieved at the underground of the baptismal chapel of the San Andrés church (Calatayud), has permitted to identify that the observed convex deformations appearing after its restoration are due to the formation of thaumasite. The formation of this complex salt requires carbonate, sulphate, silicate and calcium supply, a temperature below 15ºC and a high humidity environment. These factors have produced the crystallization of thaumasite that has led to the mortar deterioration and the appearing of expansive processes two years after the chapel restoration. The thaumasite identification has been carried out by X-ray difractometry and SEM on samples naturally dried at ambient temperature. Moreover, it has been observed that the lab routine with an 80ºC oven interferes in the mineralogical characterization because it practically destroys thaumasite decomposing it in simpler salts. The presence of thaumasite in the mortars employed for the restoration, in this case sulfate-resistant, confirms the interest in the previous constructive and geological environment analyses for the design of the restoration used material

Preparation for commissioning of materials detritiation facility at Culham Science Centre

The Materials Detritiation Facility has been designed to thermally treat solid non-combustible radioactive waste produced during operations of the Joint European Torus (JET) that is classified as Intermediate Level Waste in the UK due to its tritium inventory (> 12 kBq/g). The waste will be thermally treated in a retort furnace at temperatures up to 1000 degrees C under a flowing air atmosphere to reduce its tritium inventory sufficiently to allow its disposal at a lower waste category via existing disposal routes. The gaseous flow from the furnace will be processed via a bubbler system, where released tritium will be trapped in water. Commissioning of the facility will be divided into two main parts: inactive and active. The main purpose of the inactive commissioning is to verify that all components and safety systems of the facility are installed, tested and operated properly and within their operational limits. Several trials of the furnace with non-radioactive materials will be performed to verify its temperature profile, and to verify operation of the gaseous process line. During the active commissioning, small amounts of tritium-contaminated material will be introduced into the facility and used for active trials. The tritium inventory in this material has been selected based on the As low as reasonably practicable (ALARP) principle, to ensure that the activity levels are sufficient to fully test the control instrumentation and pose minimal risk to operators during commissioning. Overall, four active trials will be performed with carbon-based and Inconel materials with total tritium inventories of 1MBq, 3GBq, 20GBq and 26GBq. Tritium levels in the bubblers as well as in aerial discharge from the facility will be monitored. Furthermore, all materials used in the active trials will be sampled and analyzed to verify the performance of the process and confirm that a major part of tritium inventory can be removed from materials by the process

Comparison of runaway electron generation parameters in small, medium-sized and large tokamaks - A survey of experiments in COMPASS, TCV, ASDEX-Upgrade and JET

This paper presents a survey of the experiments on runaway electrons (RE) carried out recently in frames of EUROFusion Consortium in different tokamaks: COMPASS, ASDEX-Upgrade, TCV and JET. Massive gas injection (MGI) has been used in different scenarios for RE generation in small and medium-sized tokamaks to elaborate the most efficient and reliable ones for future RE experiments. New data on RE generated at disruptions in COMPASS and ASDEX-Upgrade was collected and added to the JET database. Different accessible parameters of disruptions, such as current quench rate, conversion rate of plasma current into runaways, etc have been analysed for each tokamak and compared to JET data. It was shown, that tokamaks with larger geometrical sizes provide the wider limits for spatial and temporal variation of plasma parameters during disruptions, thus extending the parameter space for RE generation. The second part of experiments was dedicated to study of RE generation in stationary discharges in COMPASS, TCV and JET. Injection of Ne/Ar have been used to mock-up the JET MGI runaway suppression experiments. Secondary RE avalanching was identified and quantified for the first time in the TCV tokamak in RE generating discharges after massive Ne injection. Simulations of the primary RE generation and secondary avalanching dynamics in stationary discharges has demonstrated that RE current fraction created via avalanching could achieve up to 70-75% of the total plasma current in TCV. Relaxations which are reminiscent the phenomena associated to the kinetic instability driven by RE have been detected in RE discharges in TCV. Macroscopic parameters of RE dominating discharges in TCV before and after onset of the instability fit well to the empirical instability criterion, which was established in the early tokamaks and examined by results of recent numerical simulations