Abstract
The α-decay of incorporated actinides continuously produces helium, resulting in helium accumulation and causing security concerns for nuclear waste forms. The helium mobility is a key issue affecting the accumulation and kinetics of helium. The energy barriers and migration pathways of helium in a potential high-level nuclear waste forms, La2Zr2O7 pyrochlore, have been investigated in this work using the climbing image nudged elastic band method with density functional theory. The minimum energy pathway for helium to migrate in La2Zr2O7 is identified as via La–La interstitial sites with a barrier of 0.46 eV. This work may offer a theoretical foundation for further prospective studies of nuclear waste forms.
Highlights
The safe disposition of the minor actinides and plutonium (Pu) generated from spent fuel, nuclear waste and dismantled nuclear weapons has become an important challenge in the development of nuclear industry [1,2]
The results show that the local environment has little influence on the behaviors of He, and the octahedral interstitial sites are the preferred positions for He to occupy in La2 Zr2 O7 pyrochlore
All DFT calculations were performed with the Vienna Ab Initio Simulation Package (VASP) [12,13] with the projector augmented wave method (PAW) [14] pseudopotentials
Summary
The safe disposition of the minor actinides and plutonium (Pu) generated from spent fuel, nuclear waste and dismantled nuclear weapons has become an important challenge in the development of nuclear industry [1,2]. Pyrochlores have attracted tremendous attention as a potential host matrix to immobilize minor actinides and Pu [3,4,5]. The α-decay of incorporated actinides produces helium (He), which is ignored. As the accumulated He will cause swelling and mitigate the physical properties of pyrochlores [6,7,8,9,10], it is essential to study He solubility, diffusion, trapping and release in pyrochlores. La2 Zr2 O7 pyrochlore, as a candidate nuclear waste form, was selected to study the effects of He in pyrochlores and compare the differences of He behavior in different local environments based on our previous work [8].
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