The project promotes trainig of young professionals through training-on-the-job funding within the Cebama work.
The following Cebama researchers have been awarded the 5 mobility measures:
|Awarded researcher||Sending organization||Hosting organization|
|Marta López García||AMPHOS 21||JUELICH|
|Enrique Rodríguez Cañas||UAM||BRGM|
|Aku Itälä||VTT||AMPHOS 21|
A summary of their stays is presented below.
My name is Jana Kittnerova and I am a PhD student at the Czech Technical University (CTU) in Prague, Czech Republic. From January 13, 2018 to April 15, 2018, I spent 3 months at the Forschungszentrum Jülich (JUELICH) in Germany within CEBAMA Mobility Measures, referring to CEBAMA WP2, radionuclide retention by high-pH concrete. This internship was part of my PhD studies at the, Faculty of Nuclear Sciences and Physical Engineering at CTU. Here, my PhD studies are focused on the interaction of cementitious materials with radionuclides, in particular radiosotopes of radium and strontium, and are led by Barbora Drtinová and Dušan Vopálka. My internship at Forschungszentrum Jülich hosted by Guido Deissmann and Steve Lange followed my previous work on the sorption of the isotopes 223Ra or 85Sr on real mortar and concrete under conditions relevant to radioactive waste disposal in the Czech Republic. In Jülich I became familiar with the synthesis, preparation and characterization (e.g. SEM, XRD) of calcium silicate hydrate (CSH) phases, the major hydration phases in cementitious materials, which I then used for experiments to get further insight into the uptake mechanisms of 226Ra, 133Ba and 90Sr in cementitious barriers. Besides these experiments we also dealt with the influence of carbonation on various cementitious materials and its consequences on the sorption properties for 226Ra. In the future I will establish the work with CSH - which I experienced in Jülich - at CTU, comparing also the results of sorption experiments with 226Ra and 223Ra (which is used as analogue of 226Ra at CTU). The outcome of this visit will provide for additional understanding of the behaviour of safety-relevant radionuclides in cementitious materials in deep geological repositories for radioactive waste.
In May/June 2018, Marta Lopéz-García, postdoctoral researcher at AMPHOS21, Barcelona, Spain, spent 2 month as guest scientist at Forschungszentrum Jülich (JUELICH), Germany, in the frame of a CEBAMA Mobility Measure, related to her work within CEBAMA WP2, radionuclide retention by high-pH concrete. The main goal of this mobility measure was to study the adsorption of Mo (as molybdate) onto specific aluminate phases representative for hydration products in cementitious materials, namely AFm and AFt and mixtures thereof, containing different anions (i.e. carbonate and sulfate). The solid phases synthesized in her home lab in Spain were characterized in JUELICH by various spectroscopic and microscopic techniques including XRD, SEM-EDX, FTIR, and RAMAN as well as by TG-DSC. The uptake kinetics of molybdate by the various AFm/AFt mixtures were investigated in specifically designed batch sorption experiments using equilibrated solid/liquid mixtures for up to 16 days under anoxic and CO2 free conditions in a glove box (Ar 99.99 %). A first analysis of the data indicates a marked difference regarding the Mo retention behavior of the different phases. In the case of samples composed mainly by AFm, Mo retention was found to be extremely effective and fast, whereas at higher AFt percentages, Mo seems only to be poorly retained. The outcome of this visit will provide for additional insights into the migration and retention behavior of Mo in cementitious barriers in repositories for nuclear wastes.
The mobility measure UAM-BRGM was planned to show some microstructural and mineralogical aspects revealed using the methodologies developed by S. Gaboreau and BRGM team studying both clay and concrete materials. One unaltered block of FEBEX bentonite/concrete was supplied by the Uni-Bern team, with the knowledge of CIEMAT (M.J. Turrero) and Nagra (F. Kober). The sample was impregnated in 14C MMA during more than 4 months in order to achieve fully access even to the smectite interlayer porosity. Then, quantitative porosity measurements can be done by autoradiography. It came evident that there is a porosity increase in concrete affecting more than 2 cm thickness from the bentonite contact. This is presumably related to the initial quality of the shotcreting. Dr. Enrique Rodríguez-Cañas (UAM) supervised by S. Gaboreau and J. Cuevas (UAM) was following at BRGM the adquisition of quantitative X-ray intensity maps and BSE images with a Cameca SX Five EPMA microscope equipped with five wavelength dispersive spectrometer (WDS). This allowed to take 512x512 pixel elemental maps with a spatial resolution of 2 µm per pixel. It is possible then to compute mineral/phase maps based on procedures of chemical segmentation using ternary scatter plot projections. Actually we are processing complete mineralogical maps in order to detect the mineralogical evolution at microscale related to the geochemical perturbation of the complex mineralogy at the bentonite-concrete.
PhD student and research scientist Aku Itälä of VTT visited Amphos 21 in Barcelona, Spain during the period of 12-16.2.2018 for cooperation with CEBAMA WP3 on modelling issues. The host was Andrés Idiart from Amphos 21 who is also the WP3 leader. On this trip Itälä presented AMPHOS some of the CEBAMA WP1 experimental results by VTT as well the CSH model developed at VTT for CSH dissolution. The model was further tested together with Andres Idiart and the complexity of the model was also simplified. Also some comparison between PHREEQC and GEM-Selektor was done.
There was discussion related to the modelling of the VTT experiments and hydration of reference cements. VTT’s CSH model was also applied to the hydration model of AMPHOS and tested the workability of the model. There was discussion about the usability of the model of VTT for low pH values (below 0.8). Role of different ion activity models and use of different databases were also clarified, especially Thermochimie database. Also there was some discussion about the relevant mineral phases in different time spans and some references were changed related to modelling of cement phases. Further co-operation and the use of VTT:s CSH model in different modelling tasks was suggested. The outcomes of this visit are being utilized to enhance the very long-term pH evolution models for Posiva’s safety case on the EBS performance expectations.
PhD student Stephan Rohmen of Forschungszentrum Jülich (JUELICH) spent two weeks at the Paul Scherrer Institute (PSI) in Villigen, Switzerland between 19.02.2018 and 02.03.2018 within the frame of the mobility measures of the CEBAMA project, related to CEBAMA WP3, Interpretation & modelling. His PhD studies, co-supervised by Andrés Idiart from AMPHOS21 and Guido Deissmann from JUELICH are focused on the development and application of a pore-scale model for the simulation of degradation processes occurring in cementitious materials (e.g. calcium leaching), to get further insights into the effects of chemical and mineralogical changes in cementitious barrier materials on its transport properties. During his stay at PSI he had the possibility to extend collaborations with other groups contributing to WP3 and exchange experiences with other researchers in the domain of pore-scale reactive transport modelling. Discussions with experts in pore-scale reactive transport modelling helped to improve the Lattice-Boltzmann based reactive transport code developed within CEBAMA called iPP. These include the usage of input data from cement hydration modelling, the implementation of a multiscale effective medium approach to model the diffusivity of C-S-H phases, or approaches to model C-S-H as ternary or quaternary solid solutions. In addition, a benchmark activity to compare the results of iPP against another reactive transport code (Yantra) has been started. Stephan was also able to attend to the 8th International reactive transport PhD workshop & CEBAMA PhD meeting which took place during his stay at PSI. The outcome and the experiences gained during his mobility measure to visit PSI will enhance the capabilities of iPP and allow for application of iPP to simulation of experiments performed within CEBAMA WP1, thus providing for an enhanced understanding of the coupling between chemical alteration processes in cementitious materials and changes in its physical properties.