Radiation damage effects in amorphous zirconolite

TL;DR

This study models radiation damage in amorphous zirconolite, revealing its structural evolution under radiation, differences from crystalline form, and potential implications for nuclear waste storage stability.

Contribution

Developed a new local coordination analysis method to study radiation effects in amorphous zirconolite, highlighting its distinct response compared to crystalline zirconolite.

Findings

Amorphous zirconolite is more 'soft' and undergoes more atomic displacements than crystalline.

Repeated radiation damage causes continuous structural evolution in the amorphous form.

Density inhomogeneities and enthalpy-coordination correlations are significant for waste storage.

Abstract

We report the results of a large-scale modelling study of radiation damage effects in the nuclear waste form zirconolite. We particularly focus on the effects of radiation damage in amorphous zirconolite and have developed a new way to analyse the damaged structure in terms of local coordination statistics. On the basis of this analysis, we find that the amorphous structure responds to radiation damage differently from the crystal. Amorphous zirconolite is found to be "softer" than crystalline zirconolite with a much larger number of atoms becoming displaced and changing coordination during a 70 keV cascade. The local coordination and connectivity analysis shows that the amorphous structure continues to evolve as a result of repeated radiation damage, changes which cannot be identified from globally averaged properties such as pair distribution functions. We also find large density inhomogeneities at the local level which we suggest may play an important role for future developments in nuclear waste storage. Finally, we find a correlation between the changes in enthalpy and local coordination, suggesting that measurements of enthalpy change can be linked quantitatively to structural radiation damage. Our results raise an interesting possibility of whether an evolution of the amorphous structure due to radiation damage can converge to a new equilibrium amorphous regime, posing the fundamental question of what that structure may be.