Coupled thermo-hydro-chemical-mechanical models for the bentonite barrier in a radioactive waste repository

Programa Oficial de Doutoramento en Enxeñaría Civil . 5011V01Versión reducida[Abstract] Compacted bentonite is foreseen in several countries as a backfill and sealing material for high-level radioactive waste (HLW) disposal. The long-term performance assessment and the evaluation of the safety of a HLW repository requires the use of numerical models dealing with the thermal (T), hydrodynamic (H), chemical (C) and mechanical (M) processes and their interplays. This dissertation presents coupled THCM models of the bentonite barrier of HLW repositories in clay and granite. The models account for the geochemical processes taking place within the bentonite as well as the interactions of the bentonite with the concrete liner and the corrosion products of the metallic canister. The THCM code INVERSE-FADES-CORE has been updated, extended to deal with reactive gaseous phases, verified and benchmarked against other codes. Coupled THCM numerical models have been applied to: 1) Small-scale heating and hydration laboratory tests performed by CIEMAT on compacted FEBEX (Full-scale Engineer Barrier Experiment) bentonite and its interactions with corrosion products and concrete; 2) FEBEX mock-up and in situ tests; 3) Long-term reactive transport model predictions of HLW repositories in granite and clay rocks. The results of the numerical models of the lab and in situ tests show a good agreement with the measured data.[Resumen] La bentonita compactada es el material previsto para el relleno y sellado de los residuos radioactivos de alta actividad (RAA) en un almacenamiento geológico profundo (AGP). La evaluación del comportamiento y de la seguridad de un AGP requiere utilizar modelos numéricos acoplados térmicos (T), hidrodinámicos (H), químicos (Q) y mecánicos (M). En esta tesis se han desarrollado modelos acoplados THQM de la barrera de bentonita para el AGP en granito y en arcilla. Los modelos tienen en cuenta los procesos geoquímicos que tienen lugar en la bentonita y sus interacciones con el hormigón y con los productos de corrosión del contenedor metálico. Los modelos se han realizado con una versión del código THQM INVERSE-FADES-CORE que se ha mejorado para tener en cuenta el transporte reactivo de gases en la fase gaseosa y se ha verificado y comparado con otros códigos. Se han realizado modelos numéricos THQM de: 1) Ensayos de laboratorio; 2) Ensayos FEBEX (Full-scale Engineer Barrier Experiment) en maqueta e in situ; 3) Predicciones de la evolución geoquímica a largo plazo de la barrera de bentonita en un AGP en granito y en arcilla. Los resultados de los modelos numéricos muestran un buen ajuste a los datos medidos.[Resumo] A bentonita compactada é o material previsto para o recheo e selado dos residuos radioactivos de alta actividade (RAA) nun almacenamento xeolóxico profundo (AXP). A avaliación do comportamento e da seguridade dun AXP precisa de modelos numéricos acoplados térmicos (T), hidrodinámicos (H), químicos (Q) e mecánicos (M). Nesta tese desenroláronse modelos acoplados THQM da barreira de bentonita para o AXP en granito e arxila. Os modelos teñen en conta os procesos xeoquímicos que teñen lugar na bentonita e a súas interaccións co formigón e cos produtos de corrosión do contenedor metálico. Os modelos fixéronse con unha versión do código THQM INVERSE-FADES-CORE que se mellorou para ter en conta o transporte reactivo de gases na fase gaseosa e que se verificou e comparou con outros códigos. Fixéronse modelos numéricos THQM de: 1) Ensaios de laboratorio de hidratación e quecemento de mostras de bentonita FEBEX (Full-scale Engineer Barrier Experiment) compactada e a súas interaccións con produtos de corrosión e formigón; 2) Ensaios FEBEX en maqueta e in situ; 3) Predicións da evolución xeoquímica a longo prazo da barreira de bentonita nun AXP en granito e arxila. Os resultados dos modelos numéricos amosan un bo axuste aos datos medido

A revisited thermal, hydrodynamic, chemical and mechanical model of compacted bentonite for the entire duration of the FEBEX in situ test

Versión aceptada de https://doi.org/10.1016/j.clay.2018.02.019[Abstract:] The safety assessment of geological repositories for radioactive waste requires quantifying the geochemical evolution of the engineered clay barriers where thermal (T), hydrodynamic (H), mechanical (M) and chemical (C) phenomena play a major role during the early stages of the repository. Compacted bentonite is one of the components of the engineered barrier system. The FEBEX (Full-scale Engineered Barrier EXperiment) in situ heating and hydration test was performed at the Grimsel underground laboratory (Switzerland) in two operation periods. The 1st period lasted from 1997 to 2002 when heater 1 was switched off and the area around it was dismantled. Heater 2 was turned off and the full test was dismantled in 2015. Here we present a revisited THCM model of the two operation periods of the FEBEX in situ test, which improves the THCM model reported by Zheng et al. (2011) for the 1st operation period by revising the boundary condition at the heater/bentonite interface, refining the spatial discretization of the finite element mesh near the heater, updating the dispersivities of the bentonite and the granite and revisiting the back-diffusion of solutes from the bentonite barrier into the granite. The concentrations of dissolved Cl− computed with the revisited model at the end of the 1st operation period almost coincide with those of the previous model, except near the heater where the concentrations computed with the revisited model are much larger than those of the previous model. Both models provide a similar fit to the pore water concentration data inferred from aqueous extracts because the model differences occur in a band 0.045 m thick near the heater where there are no measured pore water chemical data. Solute back-diffusion from the bentonite pore water to the granite groundwater is not uniform along the FEBEX gallery due to the heterogeneity of the surrounding granitic formation. The revisited model reproduces the trends of the experimental observations of solute back-diffusion by adopting diffusion coefficients of the bentonite and granite larger than those of the simulation run without the solute back-diffusion. The results of the revisited THCM model match the gravimetric water content and dry density data measured at the end of both operation periods in 2002 and 2015 and fit the general trends of the on line data of temperature and volumetric water content in the bentonite and pore water pressure in the granitic rock collected from 2002 to 2015. The predicted concentrations of the dissolved species in 2002 are sensitive to changes in the vapour tortuosity factor and the retention curve of the bentonite, but are less sensitive to smectite dissolution. The predicted concentrations of the dissolved species at the end of the 2nd operation period in 2015 computed with the revisited THCM model are large near the heater and decrease towards the bentonite/granite interface. The concentrations are generally smaller than those computed at the end of the 1st operation period, except for the concentration of dissolved HCO3– which increases due to a calcite dissolution front. The predicted pH at the end of the 2nd operation period is similar to that of the 1st operation period. The concentrations of dissolved Cl− predicted at the end of the 2nd period with the revisited model reproduce the sharp increase of the measured Cl− data near the heater and match the data measured in 5 out of 6 radial distances.The FEBEX-DP Consortium funded the dismantling operation in 2015. The support of the responsible person of the Consortium, Dr. Florian Kober, is greatly acknowledged. Additional funding by the Spanish Ministry of Economy and Competitiveness (Project CGL2016-78281-R), the FEDER funds (Project CGL2016-78281-R) and the Galician Regional Government (Ref. ED431C 2017/67 from “Consolidación e Estruturación de Unidades de Investigación Competitivas”, Grupos de Referencia Competitiva) are acknowledged. Alba Mon enjoyed a research contract from University of A Coruña. We thank the comments, corrections and suggestions of the two reviewers which contributed to the significant improvement of the paper.Xunta de Galicia; ED431C 2017/6

Dynamic update of flow and transport parameters in reactive transport simulations of radioactive waste repositories

Versión aceptada de https://doi.org/10.1016/j.apgeochem.2020.104585[Abstract:] The changes in porosity caused by mineral dissolution/precipitation and the associated changes in flow, transport and chemical parameters of porous and fractured media are relevant for the geochemical time-evolution of natural and engineered underground systems. The realistic representation of natural systems requires modeling tools accounting for the changes in porosity. Here, we investigate the significance of the dynamic upgrade of the flow, transport and chemical parameters in reactive transport models with mineral dissolution/precipitation. The water flow, heat transfer and multicomponent reactive solute transport code, CORE2DV5, was extended to take into account the changes in porosity provoked by mineral dissolution/precipitation and their effect on flow, solute transport and chemical parameters. The improvements implemented in the code were verified against analytical solutions and the numerical solutions computed with other reactive transport codes with similar capabilities for isothermal mineral dissolution/precipitation test cases. Model results computed with CORE2DV5 agree with the analytical and numerical solutions for several isothermal test cases with porosity feedback. Model results show that failing to account for the porosity feedback leads to large errors. The porosity feedback effect (PFE) is especially relevant in long-term problems with mineral dissolution/precipitation leading to strong changes in porosity. The PFE is analysed with a non-isothermal geochemically-reactive transport model of the long-term (4·104 years) interactions of compacted bentonite with corrosion products and concrete in a high-level radioactive waste repository in clay. The model predicts pore clogging in the concrete and at the concrete-clay interface. The thickness of the zone affected by pore clogging computed with the PFE is smaller than that computed without the PFE.This work was funded by the CEBAMA Project of the European Atomic Energy Community's (Euratom) Horizon 2020 Programme (NFRP-2014/2015) under grant agreement # 662147, the Spanish Ministry of Economy and Competitiveness (Project CGL2016-78281), the FEDER funds, ENRESA (Spain), and the Xunta de Galicia (Galician Regional Government, project ED431C 2017/67). The first author enjoyed a Contract from the FPI Program of the Spanish Ministry of Economy and Competitiveness. We thank the comments and corrections of the three anonymous reviewers who contributed to the improvement of the paper.Xunta de Galicia; ED431C 2017/6

Long-term non-isothermal reactive transport model of compacted bentonite, concrete and corrosion products in a HLW repository in clay

Versión aceptada de https://doi.org/10.1016/j.jconhyd.2016.12.006[Abstract:] Radioactive waste disposal in deep geological repositories envisages engineered barriers such as carbon-steel canisters, compacted bentonite and concrete liners. The stability and performance of the bentonite barrier could be affected by the corrosion products at the canister-bentonite interface and the hyper-alkaline conditions caused by the degradation of concrete at the bentonite-concrete interface. Additionally, the host clay formation could also be affected by the hyper-alkaline plume at the concrete-clay interface. Here we present a non-isothermal multicomponent reactive transport model of the long-term (1 Ma) interactions of the compacted bentonite with the corrosion products of a carbon-steel canister and the concrete liner of the engineered barrier of a high-level radioactive waste repository in clay. Model results show that magnetite is the main corrosion product. Its precipitation reduces significantly the porosity of the bentonite near the canister. The degradation of the concrete liner leads to the precipitation of secondary minerals and the reduction of the porosity of the bentonite and the clay formation at their interfaces with the concrete liner. The reduction of the porosity becomes especially relevant at t = 104 years. The zones affected by pore clogging at the canister-bentonite and concrete-clay interfaces at 1 Ma are approximately equal to 1 and 3.3 cm thick, respectively. The hyper-alkaline front (pH > 8.5) spreads 2.5 cm into the clay formation after 1 Ma. Our simulation results share the key features of the models reported by others for engineered barrier systems at similar chemical conditions, including: 1) Pore clogging at the canister-bentonite and concrete-clay interfaces; 2) Narrow alteration zones; and 3) Limited smectite dissolution after 1 Ma.The research leading to this work has received funding from the PEBS Project of the European Atomic Energy Community's Seventh Framework Programme (FP7/2007-2011) under grant agreement #232598 and the CEBAMA Project of the European Atomic Energy Community's (Euratom) Horizon 2020 Programme (NFRP-2014/2015) under grant agreement # 662147. This work was partly funded by ENRESA (Spain), the Spanish Ministry of Economy and Competitiveness (Projects CGL2012-36560 and CGL2016-78281) with support from the FEDER funds and the Galician Regional Government (Project 10MDS118028PR and Fund 2012/181 from “Consolidación e estruturación de unidades de investigación competitivas”, Grupos de referencia competitiva). The first author enjoyed a research contract from University of A Coruña and the fifth author had a Contract from the FPI Program of the Spanish Ministry of Economy and Competitiveness.Xunta de Galicia; 10MDS118028PRXunta de Galicia; 2012/18

Coupled THCM model of a heating and hydration concrete-bentonite column test

Versión aceptada de https://doi.org/10.1016/j.apgeochem.2018.05.007[Abstract:] Radioactive waste disposal in deep geological repositories in clay formations envisage a compacted bentonite engineered barrier and a concrete liner. The alkaline conditions caused by the degradation of concrete could affect the performance of the engineered barrier. The geochemical interactions occurring at the concrete-bentonite interface (B-CI) for the non-isothermal unsaturated conditions prevailing at repository post-closure have been studied by CIEMAT with a heating and hydration concrete-bentonite column test. The column consists of a 3 cm thick concrete sample emplaced on top of a 7.15 cm block of compacted bentonite. The column was hydrated through the concrete at a constant pressure with a synthetic clay porewater while the bottom of the column was heated at 100 °C. Here we report a coupled thermo-hydro-chemical-mechanical (THCM) model of the column test, which lasted 1610 days. The model was solved with a THCM code, INVERSE-FADES-CORE. Experimental observations show calcite and brucite precipitation in the concrete near the hydration boundary, portlandite dissolution and calcite and ettringite precipitation in the concrete, calcite and sepiolite precipitation in the bentonite near the B-CI, calcite dissolution in the bentonite far from the B-CI and gypsum precipitation in the bentonite near the heater. Model results attest that advection is relevant during the first months of the test. Later, solute diffusion becomes the dominant transport mechanism. Calcite and brucite precipitate in the concrete near the hydration boundary because the concentrations of dissolved bicarbonate and magnesium in the hydration water are larger than the initial concentrations in the concrete porewater. Calcite and brucite precipitate in both sides of the B-CI. Sepiolite precipitates in the bentonite near the B-CI. The model predicts portlandite and C1.8SH dissolution in the concrete. Ettringite and C0.8SH precipitate near the hydration boundary while ettringite dissolves in the rest of the concrete at very small rates. The porosity changes occur at the hydration boundary and at both sides of the B-CI due to mineral dissolution/precipitation. The porosity reduces to zero in a 0.03 cm thick zone in the concrete near the B-CI due to brucite and calcite precipitation. The high pH front (pH > 8.5) diffuses from the concrete into the bentonite and penetrates 1 cm at the end of the test after 1610 days. Model results are sensitive to grid size. Mineral precipitation and the thickness of the zone affected by mineral precipitation in the bentonite near the B-CI increase when the grid size increases while pore clogging in the concrete near the B-CI is computed only for grid sizes smaller than 0.018 cm. The non-isothermal conditions play an important role in mineral precipitation. The reduction in porosity in the B-CI for constant temperature is smaller than that of the non-isothermal run. The model reproduces the on-line measured temperature and relative humidity data as well as the water content and porosity data collected at the end of the test. Model results capture the main trends of the mineralogical observations, except for ettringite and CSH phases for which the predicted precipitation is smaller than the observed values. Model results improve when the specific surface of ettringite is increased by a factor of 10.The research leading to these results has received funding from the European Union's European Atomic Energy Community's (Euratom) Horizon 2020 Programme (NFRP-2014/2015) under grant agreement, 662147 – CEBAMA. This work was partly funded by the Spanish Ministry of Economy and Competitiveness (Grant number CGL2016-78281) with support from the FEDER funds and the Galician Regional Government (Grant number ED431C 2017/67 from “Consolidación e estruturación de unidades de investigación competitivas”, Grupos de referencia competitiva). The second author enjoyed a research contract from University of A Coruña. We thank the comments, corrections and suggestions of the Guest Editor and the two anonymous reviewers who contributed to the improvement of the paper.Xunta de Galicia; ED431C 2017/6

Reactive transport models of the geochemical interactions at the iron/bentonite interface in laboratory corrosion tests

Carbon steel and compacted bentonite have been proposed as candidate materials for the overpack and buffer, respectively, of the multi-barrier system of a geological high-level radioactive waste repository. Carbon steel corrosion may impair bentonite properties. The interactions of corrosion products and bentonite are analyzed with laboratory corrosion tests. Here coupled thermo-hydro-chemical-mechanical (THCM) models of two types of heating and hydration tests performed on compacted bentonite in contact with Fe powder are presented to study the iron-bentonite interactions at representative repository conditions. Tests on small cells (SC) were performed under unsaturated non-isothermal conditions in 25 mm long columns containing 21 mm of bentonite and 4 mm of Fe powder. Tests on medium-size cells (FB) were performed under unsaturated non-isothermal conditions in 99.8 mm long columns containing 86.8 mm of bentonite and 13 mm of Fe powder. Model results for the SC tests showed that magnetite and Fe(OH)2(s) were the main corrosion products which compete for Fe2+ precipitation. Computed corrosion products precipitate mainly in the Fe powder, penetrate a few mm into the bentonite and reproduce the measured iron weight data. Model results of the FB tests showed that magnetite precipitates throughout the Fe powder interface and reproduce the main trends of the corrosion products. Model results of these corrosion tests will be of great relevance for the performance assessment of engineered barriers of radioactive waste repositoriesThe research leading to these results was funded by ENRESA within the Work Package ACED of EURAD (European Joint Programme on Radioactive Waste Management of the European Union, grant agreement nº 847593), the Spanish Ministry of Science and Innovation (PID2019-109544RB-I00) and the Galician Regional Government (Grant ED431C2021/54). The comments and corrections of the special editor and the two anonymous reviewers are greatly appreciate

Reactive transport modelling of a low-pH concrete / clay interface

Versión aceptada de https://doi.org/10.1016/j.apgeochem.2020.104562[Abstract:] Cement-based materials are key components in the barrier system and structural support of repositories for disposal of nuclear waste. As such, increased understanding of their long-term performance under repository conditions is paramount for the safety assessment. Quantification of the impact that cement-based materials could have on the surrounding barriers and the host rock is essential to assess long-term safety of the repository system. This interaction can impact the physical properties of the system near the interface and needs to be assessed by means of numerical modelling. A reactive transport modelling study of the interaction between a newly-developed low-pH concrete and a clay host rock (i.e. Callovo Oxfordian) over 100,000 years is presented here. The main goal is to build confidence in the consistency of the different modelling approaches and in the application of different reactive transport codes (iCP, ORCHESTRA, OpenGeosys-GEM, CORE2D, and MIN3P) to analyse the performance of the recently developed low-pH concrete within the CEBAMA project. A common setup of a reference case was established, including precipitation/dissolution reactions, redox and cation exchange processes, building upon preliminary cases of increasing complexity. In addition, a set of sensitivity cases was simulated to test the effect of key geochemical and transport parameters on the results, including the impact of porosity changes on the diffusion coefficient and electrochemical couplings. Different reactive transport codes were used in the benchmark. Overall, the results show not only the high level of understanding of the governing processes but also the good agreement obtained with different codes, which is essential to demonstrate the applicability of reactive transport modelling to support safety assessment. The sensitivity and preliminary cases modelled show that the results obtained are much more sensitive to changes to transport parameters and couplings than to the different modelling tools used in each case. In addition, the impact of including or not the slow kinetics of dissolution of the claystone minerals is shown to be negligible in the studied scenarios.The research leading to these results has received funding from the European Union's European Atomic Energy Community's Horizon 2020 Programme (NFRP-2014/2015) under grant agreement, 662147 – CEBAMA. V. Montoya., J. Poonoosamy and G. Deissmann acknowledge the German Federal Ministry of Education and Research (Grant 02NUK053A) and the Initiative and Networking Fund of the Helmholtz Association (Grant SO-093) within the iCross project for partial funding. The authors would like to thank Barbara Lothenbach for fruitful discussions on modelling cement hydration of the low-pH cement system and the two reviewers for constructive and valuable comments that have helped to improve the manuscript.Alemania. German Federal Ministry of Education and Research; 02NUK053AAlemania. Initiative and Networking Fund of the Helmholtz Association; SO-09

Modelling of the long-term evolution and performance of engineered barrier system

Components of the so-called “multiple-barrier system” from the waste form to the biosphere include a combination of waste containers, engineered barriers, and natural barriers. The Engineered Barrier System (EBS) is crucial for containment and isolation in a radioactive waste disposal system. The number, types, and assigned safety functions of the various engineered barriers depend on the chosen repository concept, the waste form, the radionuclides waste inventory, the selected host rock, and the hydrogeological and geochemical settings of the repository site, among others. EBS properties will evolve with time in response to the thermal, hydraulic, mechanical, radiological, and chemical gradients and interactions between the various constituents of the barriers and the host rock. Therefore, assessing how these properties evolve over long time frames is highly relevant for evaluating the performance of a repository system and safety function evaluations in a safety case. For this purpose, mechanistic numerical models are increasingly used. Such models provide an excellent way for integrating into a coherent framework a scientific understanding of coupled processes and their consequences on different properties of the materials in the EBS. Their development and validation are supported by R&D actions at the European level. For example, within the HORIZON 2020 project BEACON (Bentonite mechanical evolution), the development, test, and validation of numerical models against experimental results have been carried out in order to predict the evolution of the hydromechanical properties of bentonite during the saturation process. Also, in relation to the coupling with mechanics, WP16 MAGIC (chemo Mechanical AGIng of Cementitious materials) of the EURAD Joint Programming Initiative focuses on multi-scale chemo-mechanical modeling of cementitious-based materials that evolve under chemical perturbation. Integration of chemical evolution in models of varying complexity is a major issue tackled in the WP2 ACED (Assessment of Chemical Evolution of ILW and HLW Disposal cells) of EURAD. WP4 DONUT (Development and improvement of numerical methods and tools for modeling coupled processes) of EURAD aims at developing and improving numerical models and tools to integrate more complexity and coupling between processes. The combined progress of those projects at a pan-European level definitively improves the understanding of and the capabilities for assessing the long-term evolution of engineered barrier systems

Ahora / Ara

La cinquena edició del microrelatari per l’eradicació de la violència contra les dones de l’Institut Universitari d’Estudis Feministes i de Gènere «Purificación Escribano» de la Universitat Jaume I vol ser una declaració d’esperança. Aquest és el moment en el qual les dones (i els homes) hem de fer un pas endavant i eliminar la violència sistèmica contra les dones. Ara és el moment de denunciar el masclisme i els micromasclismes començant a construir una societat més igualitària. Cadascun dels relats del llibre és una denúncia i una declaració que ens encamina cap a un món millor

Programa de educación en autocuidados en Cardiopatía Isquémica

Cardiac rehabilitation programmes have shown to improve the life quality and the prognosis of people with ischemic heart disease. Health education is one of the three components of this programme, along with physical fitness and psychological support. This programme’s objectives are, to promote the self-care, co-responsibility and autonomy of these patients; to improve the quality of life; to decrease, if possible, recurrences and complications. In this case, it’s about an education programme for individual-level health, intended for people who have experienced an acute myocardial infarction or a stable angina, within the last 4 months. It consists of 9 individual sessions with the primary care nurse, once a week. Each session has 3 parts: Evaluation of the adherence to therapeutic plan; assessment of the knowledge, attitude, and skills of the patient on the topic; development of the relevant educational content, including the delivery of a form summarizing the subject. The experience developed, indicates excellent results in the satisfaction of both patients and health professionals. When the intervention is right after a stroke, the patients will have high levels of motivation and adherence to the programme and to the changes of habits and attitudes. An increase in the level of knowledge and self-care capacity was also observed. Primary care nurses should actively participate in the secondary prevention of cardiovascular illnesses, by using educative structured programmes.Los Programas de Rehabilitación Cardiaca han demostrado mejorar la calidad de vida y el pronóstico de las personas con cardiopatía isquémica. La educación sanitaria es uno de los tres componentes de dichos programas, junto al entrenamiento físico y al apoyo psicológico. Los objetivos del programa son, promover los autocuidados, la corresponsabilidad y autonomía de estos pacientes; mejorar la calidad de vida; disminuir en la medida de lo posible recidivas y complicaciones. En este caso se trata de un programa de educación para la salud a nivel individual, dirigido a personas que han padecido un infarto agudo de miocardio o un ángor estable en los últimos 4 meses. Consta de 9 sesiones individuales con la enfermera de atención primaria, una vez a la semana. Cada sesión se desarrolla en tres partes: Evaluación de la adherencia al plan terapéutico; valoración de los conocimientos, actitudes y habilidades del paciente sobre el tema a tratar; desarrollo del contenido educativo correspondiente, incluyendo en esta última parte la entrega de un impreso que resume todo lo tratado. La experiencia desarrollada, nos indica excelentes resultados sobre la satisfacción tanto de pacientes como profesionales. Al realizar la intervención inmediatamente después del accidente vascular, los pacientes presentaron altos niveles de motivación y adherencia tanto al programa como a los cambios de hábitos y de actitud. Así mismo se observó un aumento del nivel de conocimientos y capacidad de autocuidado. Las enfermeras comunitarias debemos participar activamente en la prevención secundaria de la enfermedad cardiovascular utilizando programas educativos estructurados