GRaZ II: Geochemical retention of radionuclides on cement alteration phases
Helmholtz-Zentrum Dresden-Rossendorf, Institut für Ressourcenökologie
Karlsruher Institut für Technologie, Institut für Nukleare Entsorgung
Universität des Saarlandes, Anorganische Chemie
Technische Universität München, Fachgebiet Theoretische Chemie
Universität Potsdam, Institut für Chemie / Physikalische Chemie
Technische Universität Dresden, SG Strahlenschutz, Professur Radiochemie
Universität Heidelberg, Physikalisch-Chemisches Institut
The current research aligns to conditions reported by the 'AnSichT' project, which evaluated the feasibility of a repository in German clay formations . According to the developed site model 'NORD', Ca-bentonite will be used in the geo-engineered barrier as buffer and borehole sealing material. Concrete will be emplaced at different places within the repository for sealing and stabilization. Formation waters are characterized by medium to high ionic strengths . Increased salinities can lead to an enhanced degradation of concrete upon water ingress and thus promote the formation of hyperalkaline cement pore waters (10 < pH < 13). The results obtained in the previous BMWi project 'GRaZ' (no. 02E11415B) have shown that such hyperalkaline solutions can react with the bentonite buffer as well as with the surrounding clay host rock and can alter their retention potential towards uranium(VI) . Complex pore waters of increased ionic strength can affect the uranium(VI) and curium(III) retention potential of cementitious phases [4,5].
Further important parameters potentially influencing actinide retention are dissolved iron and organic ligands, released due to corrosion of steel components and concrete, respectively, of the technical barrier. Since reducing conditions are predicted for deep underground nuclear waste repositories in the long term the focus of the current studies is on reduced oxidation states of actinides. Thus, the retention of actinides (uranium, plutonium, curium) by cementitious phases of varying composition and by Ca-bentonite is studied under reducing conditions. Thereby, the influence of low molecular weight organic ligands as well as of dissolved cations (iron(II) or iron(III)) is studied. Competing effects on actinide retention or complexation will be identified and redox transformations will be quantified. The stability of actinide-doped phases at increased ionic strength is studied by applying complexly composed solutions. Furthermore, spectroscopic investigations on the binary systems uranium(VI) – organic ligand and uranium(IV) – organic ligand are performed to identify molecular structures and determine complex formation constants in the hyperalkaline pH range characteristic of cementitious-rich repositories.
This research project is performed in collaboration with the R&D projects of the cooperation partners listed above.
- Jobmann, M., Bebiolka, A., Jahn, S., Lommerzheim, A., Maßmann, J., Meleshyn, A., Mrugalla, S., Reinhold, K., Rübel, A., Stark, L., Ziefle, G.: Projekt ANSICHT - Sicherheits- und Nachweismethodik für ein Endlager im Tongestein in Deutschland - Synthesebericht, TEC-19-2016-AB, DBE Technology & GRS, Peine, Germany (2017).
- Lommerzheim, A., Jobmann, M.: Endlagerkonzept sowie Verfüll- und Verschlusskonzept für das Standortmodell NORD, TEC-08-2014-Z. DBE Technology, Germany (2014).
- Philipp, T., Shams Aldin Azzam, S., Rossberg, A., Huittinen, N., Schmeide, K., Stumpf, T.: U(VI) sorption on Ca-bentonite at (hyper)alkaline conditions – Spectroscopic investigations of retention mechanisms. Science of the Total Environment 676, 469-481 (2019).
- Wolter, J.-M., Schmeide, K., Huittinen, N., Stumpf, T.: Cm(III) retention by calcium silicate hydrate (C-S-H) gel and secondary alteration phases in carbonate solutions with high ionic strength: A site-selective TRLFS study. Scientific Reports 9, 14255 (2019).
- Wolter, J.-M., Schmeide, K., Weiss, S., Bok, F., Brendler, V., Stumpf, T.: Stability of U(VI) doped calcium silicate hydrate gel in repository-relevant brines studied by leaching experiments and spectroscopy. Chemosphere 218, 241-251 (2019).