Topic of the Master's thesis
Investigation of radiation damage in Ce/Nd-co-doped zirconates
Selina Richter
Prof. Dr. Nina Huittinen
Solid State Chemistry of Radionuclides (FWON)
05/2024–09/2024
The operation of nuclear power plants generates highly radioactive waste that requires specialized disposal methods. In Germany, the waste will be stored in a deep underground repository to ensure the isolation of radionuclides (RN) from the environment.
While spent fuel elements can be directly disposed in dry casks, RN from high level waste streams originating from nuclear fuel reprocessing plants require prior immobilization. Zirconia (ZrO2)-based ceramics are considered promising host matrices for RN immobilization because they exhibit high radiation tolerance and chemical stability. Additionally, they allow for higher waste loadings compared to the presently used borosilicate glasses.
Under ambient conditions, zirconia has a monoclinic crystal structure. The addition of other metal ions, which act as dopants and replace Zr4+ in the crystal lattice, stabilizes the higher symmetry tetragonal and cubic phases, which possess better radiation tolerance. Notably, zirconate-based pyrochlores demonstrated exceptional radiation resistance. Pyrochlores have the general formula A2B2X6YZ, where A is a trivalent rare earth element, B is a 3d, 4d, or 5d transition metal, X and Y are oxygen anions, and Z represents a vacancy. They are a superstructure of the fluorite structure, in which ordered vacancies are created due to charge mismatch. During irradiation, zirconate pyrochlores transition to the cubic defect fluorite structure, with vacancies becoming disordered over the X, Y, and Z sites.
This thesis aims to investigate the radiation tolerance of Ce/Nd-co-doped zirconates with various compositions, which were subjected to heavy ion irradiation. The research involves Raman and luminescence spectroscopy, SEM analysis, VSI, and GI-XRD measurements. It is part of the AcE project (Fundamental investigations of Actinide immobilization by incorporation into solid phases relevant for final disposal), funded by the BMBF.
