Contact

Prof. Dr. Nina Maria Huittinen

Head Solid State Chemistry of Radionuclides
n.huittinenAthzdr.de
Phone: +49 351 260 2148

Solid State Chemistry of Radionuclides Department


Research

Foto: Icon der Abteilung Festkörperchemie von Radionukliden des IRE ©Copyright: Prof. Dr. Nina Maria Huittinen

As the name implies, the Solid State Chemistry of Radionuclides department focuses on research related to the structure and properties of solid phases containing radioactive elements. We are especially interested in crystalline inorganic solid phases such as zircon (ZrSiO4), zirconia (ZrO2), and pyrochlore (Ln2Zr2O7), as well as lanthanide (Ln-)orthophosphates of the monazite type (LnPO4). These solid phases are of relevance in the corrosion of the Zircaloy cladding surrounding spent nuclear fuels rods, or they are envisioned as ceramic hosts for the immobilization and safe disposal of specific actinide-bearing waste streams generated in the late stages of the nuclear fuel cycle. We produce polycrystalline powders or single crystals doped with actinide elements using hydrothermal, flux growth, and solid-state synthesis routes. Combining X-ray diffraction and various microscopic and spectroscopic techniques, we explore the microstructure, redox chemistry, and local structural order/disorder phenomena in the doped solid phases. With this, we aim to develop a detailed understanding of actinide immobilization in crystalline matrices on an atomic basis and to make reliable statements with regard to the performance of the host materials under repository conditions.


Latest Publication

Self-healing ThSiO4-ZrSiO4 system under conditions relevant to underground nuclear waste repositories

Svitlyk, V.; Weiß, S.; Garbarino, G.; Shams Aldin Azzam, S.; Hübner, R.; Worbs, A.; Huittinen, N. M.; Hennig, C.

Abstract

Two series of Th1-xZrxSiO4 phases were synthesized hydrothermally under weakly basic (pH = 8) and strongly acidic (pH = 1) conditions. Changes in pH were found to have a significant effect on experimental phase diagrams. Synthesis at pH = 8 favors the formation of Th-rich phases with resulting Th1-xZrxSiO4 solid solution for x = 0 – 0.5. Contrary, synthesis at pH = 1 results in the formation of pure end-members of the ThSiO4-ZrSiO4 pseudo-binary system separated by multiple miscibility gaps. Phases formed both under basic and acidic conditions were found to retain water, which can be discharged from the structure upon heating. A different high-pressure (HP) behaviour was found for Th-rich and Zr-rich solid solutions. While Th-rich Th0.9Zr0.1SiO4 and Th0.6Zr0.4SiO4 phases retain their stoichiometry and crystal structure upon compression at HP, a significant reduction of the Th occupancy related to a decrease of the Th-O distances is observed for the Th-poor Th0.26Zr0.74SiO4 phase at P > 8 GPa, with the subsequent formation of a Th-rich amorphous phase. The Th diffusion between the crystalline and amorphous phases was found to be fully reversible. This unique self-healing property makes these phases promising candidates for nuclear applications under extreme pressure and temperature conditions, in particular those found in underground repositories.

Involved research facilities

Related publications

Permalink: https://www.hzdr.de/publications/Publ-39571


More publications


Latest publication

Self-healing ThSiO4-ZrSiO4 system under conditions relevant to underground nuclear waste repositories

Svitlyk, V.; Weiß, S.; Garbarino, G.; Shams Aldin Azzam, S.; Hübner, R.; Worbs, A.; Huittinen, N. M.; Hennig, C.

Abstract

Two series of Th1-xZrxSiO4 phases were synthesized hydrothermally under weakly basic (pH = 8) and strongly acidic (pH = 1) conditions. Changes in pH were found to have a significant effect on experimental phase diagrams. Synthesis at pH = 8 favors the formation of Th-rich phases with resulting Th1-xZrxSiO4 solid solution for x = 0 – 0.5. Contrary, synthesis at pH = 1 results in the formation of pure end-members of the ThSiO4-ZrSiO4 pseudo-binary system separated by multiple miscibility gaps. Phases formed both under basic and acidic conditions were found to retain water, which can be discharged from the structure upon heating. A different high-pressure (HP) behaviour was found for Th-rich and Zr-rich solid solutions. While Th-rich Th0.9Zr0.1SiO4 and Th0.6Zr0.4SiO4 phases retain their stoichiometry and crystal structure upon compression at HP, a significant reduction of the Th occupancy related to a decrease of the Th-O distances is observed for the Th-poor Th0.26Zr0.74SiO4 phase at P > 8 GPa, with the subsequent formation of a Th-rich amorphous phase. The Th diffusion between the crystalline and amorphous phases was found to be fully reversible. This unique self-healing property makes these phases promising candidates for nuclear applications under extreme pressure and temperature conditions, in particular those found in underground repositories.

Involved research facilities

Related publications

Permalink: https://www.hzdr.de/publications/Publ-39571


More publications


Team