LES Research Projects
Modern spent fuel dissolution and chemistry in failed container conditions (DISCO)
The EURATOM Project “DISCO” (modern spent fuel DISsolution and chemistry in failed COntainer conditions), carried out within the Horizon2020 framework program, is a collaborative effort among European partners aiming at increasing the knowledge on spent fuel dissolution under repository-relevant conditions (highly reducing conditions). Experimental work will focus on dissolution studies of so-called "modern" fuels, i.e. fuels doped with alumina/chromia or mixed oxide fuels. Both types of fuels are increasingly used in operating light water reactors in order to optimize energy harvesting. However, these fuels may potentially pose repository-related problems due to their different microstructure and the higher content of fission products, induced by the higher burnup compared to conventional UO2 fuels. The major objective of the project is to understand the dissolution behaviour of modern fuels in a water-flooded failed canister under anoxic repository conditions. Dissolution experiments on real spent fuel will be complemented by work on surrogate materials mimicking compositional and microstructural properties of the fuels, as well as by a series of dedicated modelling studies. PSI's contribution will be entirely on the theoretical side and consists of the following two major tasks:
(I) thermodynamic modelling of modern fuels under in-reactor conditions, taking into account the non-stoichiometry of (U,Pu)O2±x and mixing with other actinides and additives (alumina/chromia);
(II) thermodynamic modelling of secondary phase formation inside the failed canister, again with focus on solid solution formation.
Thermodynamic and spectroscopic investigations of the Fe and S speciation in anoxic cementitious systems
Supervisors: Dr. E. Wieland and Dr. R. Dähn (Paul Scherrer Institut, LES), Dr. B. Lothenbach (Empa), Prof. B. Wehrli (ETH Zürich)
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.
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.
THEREDA (Thermodynamic Reference Database)
Contact person: Tres Thoenen
Duration: 1.10.2015 - 31.12.2020
In the framework of THEREDA, LES is responsible for the thermodynamic data related with cementitious systems.
Project: Diffusion in argillaceous rocks
Project: Traphiccs (Transport phenomena in compacted clay systems)
Project: GEMS TM (Gibbs Energy Minimization Software for Thermodynamic Modelling)
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
Contact persons: Dan Miron (Postdoc), Dmitrii Kulik, Tres Thoenen
Duration: 1.3.2015 - 30.04.2020
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.
Roloc (Retardation of low-molecular weight organic compounds in clay)
Supervisors: Dr. M. Glaus, Dr. L. Van Loon, Dr. E. Wieland (Paul Scherrer Institut, LES) Dr. U. Mäder, Universität Bern
Anion Accessibility in Low Porosity Argillaceous rocks (ANPOR)
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.
Porosity and structural changes at cement/clay interfaces and their relation to transport properties
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)
Experimental benchmarks for the verification and validation of reactive transport codes
Supervisors: Dr. G. Kosakowski, Dr. L. Van Loon (Paul Scherrer Institut, LES) Dr. U. Mäder (University of Bern)