Verhalten langlebiger Spalt- und Aktivierungsprodukte im Nahfeld eines Endlagers und Möglichkeiten ihrer Rückhaltung (VESPA)

Summary

Long-term safety assessments for final disposals of high level radioactive waste have to include the consideration of the release of radionuclides from the waste and their potential retention by the multi barrier system. To date, it has been assumed in long-term safety analysis that there is only retention for cationic but not for anionic species within the near field of final disposals.

In this context, the joint research project VESPA, had the primary objective to investigate the retention of ¹⁴C, ⁷⁹Se, ¹²⁹I and ⁹⁹Tc. In aquatic solutions, these elements mainly occur in anionic form and do not form poorly soluble phases.

Objective of the sub project of the HZDR was the identification of processes leading to retention of the fission product ⁷⁹Se. Sorption of Se on mineral phases as well as aquatic Se speciation in the presence of different salts (NaCl, CaCl₂, MgCl₂) have been focus of the investigations. The experiments were concentrated on parameter ranges relevant for final repositories in salt and clay formations. Additional to batch experiments, a spectroscopic identification of surface species, required for surface complexation modeling, has been an important part of the investigations. Geochemical conditions and temperature have a significant influence on the sorption of radionuclides. These circumstances have been complied with investigations on the impact of different salt concentrations and different temperatures of the fluid.

The project made a major contribution to the databases needed for safety analyses of final repositories.

Figure: Fourier transform magnitude spectra (left) and the two observed ¹E and ²C surface complexes (right) upon Se(IV) adsorption onto maghemite.

Publications

Journal paper

• J. Kretzschmar, N. Jordan, E. Brendler, S. Tsushima, C. Franzen, H. Foerstendorf, M. Stockmann, K. Heim, V. Brendler: "Spectroscopic evidence for selenium(IV) dimerization in aqueous solution", Dalton Transactions, (2015<), 44, 10508-10515.
• Jordan, N.; Ritter, A.; Scheinost, A. C.; Weiß, S.; Schild, D.; Hübner, R. (2014) "Selenium(IV) uptake by maghemite (γ-Fe₂O₃)". Environmental Science & Technology 48, 1665-1674.
• Jordan, N.; Müller, K.; Franzen, C.; Brendler, V. (2013) "Temperature impact on the sorption of selenium(VI) onto anatase." Journal of Colloid and Interface Science 390, 170-175.
• Jordan, N.; Ritter, A.; Foerstendorf, H.; Scheinost, A. C.; Weiß, S.; Heim, K.; Grenzer, J.; Mücklich, A.; Reuther, H. (2013) "Adsorption mechanism of selenium(VI) onto maghemite." Geochimica et Cosmochimica Acta 103, 63-75.

Talks:

• Franzen, C., Hering, D., Jordan, N., Weiss, S., Retention of selenium oxyanions at the water-mineral interface in the context of nuclear waste repositories. IMA 2014, 21^st General Meeting of the International Mineralogical Association (01.-05.09.2014, Gauteng province, South Africa).
• Foerstendorf, H., Jordan, N., Heim, K., Surface speciation of dissolved radionuclides on mineral phases derived from vibrational spectroscopic data. 248^th ACS National Meeting & Exposition (10.-14.08.2014, San Francisco, U.S.A.)
• Jordan, N., Domaschke, S., Foerstendorf, H., Scheinost, A. C., Franzen, C., Zimmermann, V., Weiß, S., Heim, K., Uptake of selenium oxyanions by hematite. Goldschmidt 2014 (08.-13.06.2014, Sacramento, USA).
• Foerstendorf, H., Gückel, K., Jordan, N., Rossberg, A., Brendler, V., Surface speciation of dissolved radionuclides on mineral phases – A vibrational and X-ray absorption spectroscopic study. 5^th Asia-Pacific Symposium on Radiochemistry (APSORC 13) (22.-27.09.2013, Kanazawa, Japan).
• Jordan, N., Ritter, A., Foerstendorf, H., Scheinost, A.C., Heim, K., Weiß, S., Brendler, V., Sorption of Se(VI) and Se(IV) oxyanions onto maghemite: a macroscopic and spectroscopic study. SELEN 2012- Selenium in geological, hydrological and biological systems (08.-09.10.2012, Karlsruhe, Deutschland).
• Franzen, C., Hering, D., Jordan, N., The impact of salinity on the sorption of selenate onto aged γ-Al₂O₃ in the context of salt dome repositories. European Mineralogical Conference. (02.-06.09.2012, Frankfurt, Deutschland).
• Franzen, C., Jordan, N., Müller, K., Influence of Temperature on the Sorption of Selenate onto Anatase. Experimental Mineralogy, Petrology and Geochemistry (04.-07.03.2012. Kiel, Deutschland).

Posters:

• Jordan, N., Domaschke, S., Zimmermann, V., Foerstendorf, H., Scheinost, A. C., Weiß, S., Heim, K., Sorption of selenium oxyanions onto hematite. 14th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere (08.-13.09.2013, Brighton, United Kingdom).
• Franzen, C., Hering, D., Jordan, N., Retention of selenate at the water-mineral interface in the context of salt dome repositories. Goldschmidt 2013 (25.-30.08.2013, Florence, Italy).
• Kretzschmar, J., Jordan, N., Brendler, E., ⁷⁷Se-NMR spectroscopic investigations on aqueous selenium speciation at higher temperatures and in the presence of divalent metal ions. EURACT-NMR Workshop (17.-19.07.2013, Karlsruhe, Germany).
• Franzen, C.; Jordan, N.; Müller, K.; Meusel, T.; Brendler, V., Temperature Impact on the Sorption of Selenate onto Anatase. HiTAC Workshop (09.11.2011, Karlsruhe, Deutschland).
• Jordan, N., Foerstendorf, H., Scheinost, A. C., Lützenkirchen, J., Schild, D., Weiß, S., Heim, K., Brendler, V., Uptake of selenium(VI) and selenium(IV) onto anatase. Geological Disposal of Radioactive Waste: Underpinning Science and Technology (18.-20.10.2011, Loughborough, England).
• Jordan, N., Müller, K., Franzen, C., Foerstendorf, H., Weiß, S., Heim, K., Brendler, V., 13^th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere (18.-23.09.2011, Beijing, China).