LES Research Projects

Thermodynamic and spectroscopic investigations of the Fe and S speciation in anoxic cementitious systems

PhD Project: Andrea Mancini
Supervisors: Dr. E. Wieland and Dr. R. Dähn (Paul Scherrer Institut, LES), Dr. B. Lothenbach (Empa), Prof. B. Wehrli (ETH Zürich)
The objective of this project is to gain a better understanding of the interaction of iron and cement and the long-term behaviour of cement paste under anoxic conditions. The adsorption of reduced iron and sulphur species on cement phases and the possible formation of solid solutions (solid solutions) will be investigated in laboratory studies and complemented by synchrotron-based spectroscopic in situ measurements of the iron and sulphur speciation in slag cements. The project is expected to generate new and important information about the interaction of iron and sulphur species with cement paste at the micro scale which helps in developing thermodynamic models for cementitious systems under anoxic conditions. These models are essential to assess more comprehensively the long-term stability of slag cements and the long-term development of cement as a barrier material in a deep geological repository for radioactive waste. Top

Cebama

Cebama is a collaborative project funded by the European Commission under the Horizon 2020 Research and Training Program of the European Atomic Energy Community (EURATOM). This project addresses key scientific questions related to the use of cement-based materials in nuclear waste repositories including interface processes between cement-based materials and host rocks, retention of high priority radionuclides, and the development of models predicting changes in transport properties of cement-based materials. Within this project, LES carries out two different studies:

A structural and thermodynamic study on the intercalation of selenium(IV), selenium(-II), sulfur(-II) and iodine(-I) in hydrocalumite-type phases (AFm phases)
Contact persons: Latina Nedyalkova (PhD student), Jan Tits
Duration: 1.1.2016 - 31.12.2018
79Se and 129I are important dose determining radionuclides and their long-term behavior in a deep geological repository for low and short-lived intermediate level waste (L/ILW) is of major interest due to their long half-lifes and their potential mobility in the geosphere. However, such predictions on the mobility of these anions ignore their potential retardation by positively charged anion exchangers present in cementitious materials such as ettringite and hydrocalumite-like phases (AFm-phases). This study proposes an investigation of the immobilization of Se and I by AFm-phases under oxidizing and reducing conditions. In addition, the competitive effects of other anions such as CO32- and S2- on the immobilization of Se and I will be studied. Previous studies carried out at LES have shown that, under specific conditions, Se and I can become intercalated in the AFm interlayers. The present project consists of a systematic investigation of Se(IV), Se(-II), S(-II), and I(-I) intercalation in AFm phases. Thermodynamic models describing the intercalation of these anions in AFm phases will be developed based upon wet chemistry data and structural information from X-ray diffraction, Rietveld refinement and X-rax absorption spectroscopy.Top

Modelling transport across reactive interfaces
Contact persons: Leonardo Hax Damiani (PhD student), Georg Kosakowski
Duration: 1.1.2016 - 31.12.2018
Knowledge on the temporal and spatial evolution of alterations near interfaces between clay and cement based materials is important for the performance assessment of deep geological repositories for radioactive waste. All chemical reactions solely proceed if a stagnant or mobile aqueous phase is present in sufficient quantity. Chemical gradients, here in particular emanating from the strongly alkaline cementitious materials, dictate the reaction courses, and the principles of chemical thermodynamics determine the fundamental reaction products of the interactions. The goal of the sub-project is the development of improved 2D and 3D conceptual and numerical models that consider the influence of charged mineral surfaces on chemical and transport processes. The improved models will be tested and used by analyzing experiments on interactions of concrete with clays or other materials. Top

ThermAc

Contact persons: Dan Miron (Postdoc), Dmitrii Kulik, Tres Thoenen
Duration: 1.3.2015 - 28.02.2018
The Joint Project ThermAc aims at extending the chemical understanding and thermodynamic database of actinides, long-lived fission products and important matrix elements in aquatic systems at elevated temperatures. For this purpose, a systematic use of estimation methods for thermodynamic data missing at elevated temperatures, new experimental investigations of relevant aqueous species and solids, and quantum-chemistry based simulations are carried out. The project is funded by the German Federal Ministry for Education and Research and comprises the following partners: Karlsruhe Institute of Technology (KIT-INE), Helmholtz Zentrum Dresden Rossendorf (HZDR-IRE), University of Heidelberg, Gesellschaft für Anlagen- und Reaktorsicherheit (GRS Braunschweig), Jülich Research Center (FZJ-IEK-6), Technische Universität München, Amphos21 Barcelona, and Paul Scherrer Institut Villigen (PSI-LES).
Within this project, LES carries out two complementary investigations:
1) Systematic evaluation and application of isocoulombic reaction equilibria for extrapolation of equilibrium constants to higher temperatures
Thermodynamic data for actinides and long-lived fission products are generally only known from experiments at room temperature. Since it is not possible to extend the validity range of all relevant data within a reasonable timeframe by carrying out experiments at elevated temperatures, one has to resort to estimation methods. The isocoulombic estimation method has the potential to fill important gaps.
2) Software package integration for managing, estimating, fitting, and calculating thermodynamic data as a function of temperature (and pressure)
For an efficient evaluation and application of the isocoulombic estimation method, three existing, separate software packages developed by LES, namely PMATCHC (thermodynamic database management), GEMS-PSI (modelling of complex geochemical systems), and GEMSFITS (fitting and optimization of thermodynamic parameters) shall be integrated into a coherent framework, where PMATCH++ (a complete revision of PMATCHC, based on the graph-database paradigm) shall serve as a central distribution hub for thermodynamic data and shall support searching and manipulating substance- and reaction-data to generate a broad selection of alternative isocoulombic reactions. Top

THEREDA (Thermodynamic Reference Database)

Contact person: Tres Thoenen
Duration: 1.10.2015 - 31.12.2017
On 1.10.2015 LES has become a partner of THEREDA (Thermodynamic Reference Database), a project organized and carried out by the most relevant research institutions in the field of radioactive and chemotoxic waste disposal in Germany (GRS Braunschweig, KIT-INE Karlsruhe, HZDR-IRE Dresden-Rossendorf, and TU-BAF Freiberg) and currently financed by the Federal Office for Radiation Protection (BfS). THEREDA was started in 2006 with the main objective to establish a comprehensive and internally consistent thermodynamic database for the geochemical modeling of processes occurring in the near- and far-field of the different hostrock formations under discussion in Germany for the long-term underground storage of radioactive waste. At that time, rock-salt formations were the only type of host rock considered and the main objective of THEREDA has been the critical evaluation and provision of data which support the calculation of solubilities in highly-saline aqueous solutions. Thus, standard thermodynamic data selected in THEREDA are consistent with Pitzer ion interaction coefficients. The internal data structure of THEREDA is designed to be quite general, so that an extension of the database for other potential types of host rocks requiring other types of ion interaction parameters (e.g. SIT, or Debye-Hückel) is possible.
In the framework of THEREDA, LES is responsible for the thermodynamic data related with cementitious systems. Top

Roloc (Retardation of low-molecular weight organic compounds in clay)

PhD Project: Yanhua Chen
Supervisors: Dr. M. Glaus, Dr. L. Van Loon, Dr. E. Wieland (Paul Scherrer Institut, LES) Dr. U. Mäder, Universität Bern
In this project potential mechanisms for the retardation of low-molecular weight organic compounds are investigated. The project is embedded in the general activities in LES to understand the fate of 14C compounds released from irradiated steel and to quantify their possible contribution to the overall dose in a safety assessment. Top

Anion Accessibility in Low Porosity Argillaceous rocks (ANPOR)

PhD Project: Cornelia Wigger
Supervisors: Dr. L. Van Loon, Dr. T. Gimmi (Paul Scherrer Institut, LES) Dr. U. Mäder, Universität Bern
The objective of this PhD project is to investigate the diffusive behaviour of anions in argillaceous rocks. Anions are known to be repulsed from the negatively charged surface of clay minerals. Due to this phenomenon, only a part of the pore space in argillaceous materials is accessible for anionic species. The extend of anion exclusion observed in several clay rocks lies around 50% of the total porosity. Because interlayer containing clay minerals are largely absent in argillaceous rocks, interlayers cannot be made responsible for this large anion exclusion as in the case of compacted bentonite. A plausible explanation for the observed phenomena in clay rocks maybe the fact that, due to the very high degree of compaction of clay rocks, the pores are so narrow that they behave as interlayers, i.e. an important part of the charged pores in clay rocks are interlayer equivalent pores (ILE) that are – in analogy to interlayer pores - not accessible for anions. The pores that are accessible for anions are not or only weakly charged. Top

Project: Diffusion in argillaceous rocks

Contact person: Luc Van Loon
Within the framework of the Sectoral Plan (Sachplan geologische Tiefenlagerung) diffusion measurements with differently charged and uncharged radiotracers are carried out in intact samples of potential host rock material, such as Opalinus Clay, Brauner Dogger, Effingen members, etc. The major issues are obtaining diffusion parameters under realistic conditions (e.g. by appropriately taking into account effects of layering of the clay platelets and the pressure under in-situ conditions), testing the applicability of these data on different scales of space and time and to provide sorption data on intact clay rock samples. Classical mass transfer experiments with radiotracers are supplemented by spectroscopic (e.g. neutron scattering and diffraction) or microscopic (e.g. X-ray tomography) techniques for this purpose. All these efforts are directed towards the goal of developing a generic knowledge on diffusion processes, by which it will be possible to predict radionuclide diffusion in a rock material for which some key properties, such as the clay content and clay mineral composition or the porosity, are known. Top

Project: Traphiccs (Transport phenomena in compacted clay systems)

Contact person: Martin Glaus
The Traphiccs project addresses fundamental questions related to the transport of charged species in charged clay minerals. It is known that effective diffusion coefficients for such media cannot be directly derived from bulk water diffusion coefficients. Rather it has been observed that diffusive fluxes of anions are lower and those of certain cations, particularly those of the alkali and earth alkali series, higher than expected from such a simple model. While the diffusion of more strongly sorbing elements in compacted clay minerals has been measured since a couple of decades, the interpretation of these results is based on apparent diffusion coefficients only. These quantities lump together transport properties (effective diffusion coefficients) and sorption properties (sorption distribution values). Various experimental techniques were developed at LES in order to obtain separate information on these parameters. This allows for giving an indiscriminate answer to the question of whether sorption measurements on disperse clay suspensions give the same results as measurements on intact rock or compacted clay samples. Top

Project: Catclay

Contact persons: Luc Van Loon, Martin Glaus
Catclay is a 7th framework EU research project specifically dedicated to the question of whether the diffusion rates of metal cations from the transition metal or the lanthanide series in compacted clay minerals and clay rocks may be enhanced by surface phenomena. LES contributes to this project by diffusion measurements with radiotracers in which the typical problems related to sample confinement and ambiguities in the conceptual description of the results were avoided. Appropriate diffusion cells for confining compacted illite or Opalinus Clay samples were constructed. The results obtained so far indicate that the diffusive rates measured e.g. for Co(II) and Zn(II) are actually larger than expected from a simple pore diffusion model based in which the effective diffusion coefficients are derived from diffusion coefficients valid for bulk water. Top

Project: FIRST Nuclides

Contact person: Enzo Curti
The EURATOM FP7 Project “Fast / Instant Release of Safety Relevant Radionuclides from Spent Nuclear Fuel (FIRST Nuclides)” is a collaborative effort among European partners with the objective of increasing the database and the mechanistic understanding on the fast released radionuclides (the so called Instant Release Fraction, IRF) from high burn-up UO2 spent nuclear fuel under geological disposal conditions. It started on January 1st, 2012 and will end officially on December 31th, 2014. The project provides for experiments, carried out in facilities specialised with handling highly radioactive materials, combined with modelling studies to integrate the different results and up-scale from laboratory to disposal conditions. PSI-LES is involved with two major tasks: (I) Evaluate the IRFs of 135Cs, 129I, 79Se and 14C based on in-house aqueous leaching experiments on UO2 spent fuel and cladding fragments from Swiss reactors (Leibstadt and Gösgen). (II) Study the chemical state of selenium (specifically its oxidation state) in high burnup UO2 spent fuel by X-ray spectroscopic techniques. Top

Project: COTHERM

Contact person: Dmitrii Kulik
The SNF Sinergia COTHERM project (COmbined hydrological, geochemical and geophysical modeling of geotTHERMal systems) aims at a better understanding of the subsurface processes in natural high-temperature hydrothermal systems that are an attractive alternative energy resource. The project started on September 1'st 2012 and will finish by the end of 2015. Using the examples of two different geothermal systems in Iceland that have been drilled for geothermal energy exploitation, COTHERM pursues four interconnected sub-projects to advance our knowledge about these systems and to improve relevant geochemical and geophysical techniques: (1) Computer simulations to understand how strongly the water gets heated and how much hot water can flow through different rock types and in different geological Settings. (2) Computer-aided reactive-transport modelling of how fast the hot water can dissolve minerals from the rock and precipitate others, which may influence the hot water pathways. (3) Use of the rock properties and flow path predictions from sub-projects (1) and (2) to find out how geophysical methods could be used to probe the underground system structure without drilling. (4) Collect geochemical, mineralogical, and geophysical data to compare simulation results of sub-projects (1) to (3) with the actual data in order to refine, validate, and integrate different approaches. Our task (sub-project 2) in COTHERM consists in investigating and modelling basaltic rocks alteration upon hydrothermal fluid circulation, considering factors such as: fluid recharge composition, magmatic gas amount, primary rock mineralogy, and flow path geometry and temperature distribution. We are trying to constrain the kinetics of primary minerals dissolution and of secondary minerals precipitation, and to demonstrate the value of considering secondary minerals precipitation kinetics in reactive transport simulations using the in-house OpenGeoSys-GEMS coupled codes. Top

Project: C-14

Contact persons: Erich Wieland, Benjamin Cvetkovic
Duration: 1.4.2013 - 31.10.2016
Activated steel is the main source of 14C in a repository for low and short-lived intermediate level waste (L/ILW). In a deep geological repository 14C will be released from activated steel during anoxic steel corrosion and, according to current PA studies, is an important dose determining radionuclide. The chemical nature of the 14C species present in the cementitious near field is poorly known. The project comprises the development of a compound-specific 14C AMS technique to identify and quantify 14C containing organic compounds at very low concentrations and a corrosion experiment with activated steel under repository relevant conditions. The project is partially financed by swissnuclear and the EU FP7 project “CAST” (CArbon Source Term). The project is carried out in collaboration with PSI (Hot laboratory, Laboratory of Radiochemistry & Environment Chemistry at PSI/University of Bern, Switzerland) and external partners (Institute for Chemistry and Bioanalytics, University of Applied Sciences Northwestern Switzerland) Top

Project: GEMS TM (Gibbs Energy Minimization Software for Thermodynamic Modelling)

Contact person: Dmitrii Kulik
Since the year 2000, GEMS has evolved into a cooperative R&D project aimed at creating a software collection of choice for computer-aided thermodynamic modeling of complex (geo)chemical systems. The goal of modeling with GEMS is to improve our understanding of chemical processes and systems by predicting their evolution at various TPbt conditions (T: temperature, P: pressure, b: bulk composition, t: time). GEMS has been used in many relevant research projects at LES related to radioactive waste disposal; in other laboratories at NES and at other departments of PSI, in other institutes of the ETH Domain, and in several universities worldwide (160 citations just since 2013). Many people switch to GEMS due to specific advantages after using other codes such as MINEQL or PHREEQC.
The numerical engine of GEMS - the GEMS3K code - can solve for equilibrium speciation in systems involving aqueous electrolyte; non-ideal gaseous fluids; non-ideal solid solutions; non-ideal (ionic) melts; adsorption, ion exchange; many pure phases (solid, liquid); and many metastable species or phases. Only with GEM method one can solve such complex equilibria of relevance for waste repositories, geothermal energy, reactive transport and geochemistry. At the same time, GEMS can solve for simple speciation in aquatic systems just as other codes like PHREEQC do. GEM needs thermodynamic data for all species in the system, not only logK of formation of product species from master species as the other codes need. Thus, GEMS can extract more results from the input data, such as redox states (Eh, pe) directly computed from the bulk elemental composition b.
The GEM-Selektor – a graphical user interface of GEMS3K - greatly facilitates definition of the system, input of composition recipes, computation of single equilibrium states or process simulations, viewing/exporting the results as tabulated data or plots, and managing the thermodynamic data. It is therefore an educational tool, at the same time providing the fast way to visualise thermodynamic problems and solutions. System definitions can be exported per mouse click into files for use in coupled codes such as the GEMSFITS code for input parameter optimization, and reactive-transport codes Comsol-GEM, OpenGeoSys-GEM and CSMP++GEM. The GEMS is distributed from http://gems.web.psi.ch as freemium, in part open-source software together with built-in PSI/Nagra and SUPCRT98 thermodynamic databases. Several third-party thermodynamic databases (e.g. Cemdata’14, HERACLES, Mines’16), maintained by their respective owners, are also available as plugins.
GEMS is attracting students and researchers: there is an interdisciplinary community formed around it (>4000 downloads and >300 active users worldwide). The GEMS Development Team currently involves 11 members from 6 institutions. This team strives to implement innovative concepts, modern algorithmic frameworks, and tools to improve thermodynamic data, all in order to ensure the state-of-the-art functionality of GEMS for the next decade.

Past LES Research Projects

Porosity and structural changes at cement/clay interfaces and their relation to transport properties

PhD Project: Amir Shafizadeh
Supervisors: Dr. Th. Gimmi, Dr. L. Van Loon, Dr. S. Churakov (Paul Scherrer Institut, LES), Dr. A. Kaestner and Dr. E. Lehmann (NIAG group-PSI), Dr. U. Mäder (University of Bern)
In the Swiss concept of geological repositories for radioactive waste, cement and concrete materials will come into direct contact with clay rocks. The geochemical gradients between clay and cement cause diffusive mass flux across the interface. These fluxes and consequent chemical changes in backfill materials need to be quantified in order to assess the long-term safety of the disposal sites. In this project the mineralogical and structural evolution (dissolution/precipitation of minerals, porosity changes) at the cement/clay interfaces are monitored by using different, complementary experimental techniques such as neutron tomography, radiography (at ICON facility, PSI) and measurement of transport parameters using through-diffusion tracer experiments Top

Experimental benchmarks for the verification and validation of reactive transport codes

PhD Project: Jenna Poonoosamy
Supervisors: Dr. G. Kosakowski, Dr. L. Van Loon (Paul Scherrer Institut, LES) Dr. U. Mäder (University of Bern)
The evolution of porosity due to mineral alteration processes and the associated change of transport parameters are of major concern for natural geological environments or engineered underground disposal systems. In numerical models, which calculate porosity changes from dissolution/precipitation of minerals, the temporal evolution of porosity is highly affected by reaction kinetics and numerical mesh refinement. In addition, such numerical models use empirical relations for linking porosity with transport properties (e.g. diffusivity and permeability). The numerical models need to be tested with experiments to confirm their predictions of geochemical migration affected by porosity changes. The aim of my PhD is to set up 1D and 2D reactive transport experiments in simple media, where clogging is fostered and its evolution with time can be easily assessed. These experiments are modeled with the reactive transport code OpenGeosys-GEM (OGS-GEM). Top