A First-Principles Density Function Theory Study of Tritium Diffusion in Li₂ZrO₃: Application for Producing Tritium

Journal Article · Mon Nov 26 00:00:00 EST 2018 · Journal of Physical Chemistry. C

DOI:https://doi.org/10.1021/acs.jpcc.8b05810· OSTI ID:1573894

Paudel, Hari P. ^[1]; Duan, Yuhua ^[1]

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1. National Energy Technology Lab. (NETL), Pittsburgh, PA (United States)

The ceramic material Li₂ZrO₃ has superior thermo-physical and thermo-chemical properties and is highly compatible with other blanket materials used in nuclear reactors. Like LiAlO₂, it could be used in the form of an annular pellet in tritium-producing burnable absorber rods (TPBARs) to produce tritium(³H) upon thermal neutron irradiation of lithium isotope (⁶Li). The radiation damaged pellet crystal contains vacancies, defects of its constituent elements, and several other trapping sites which hinder the ³H diffusion process and releasing behavior. In this study, we investigate the diffusion mechanisms of ³H and O³H species in Li₂ZrO₃ ceramic pellet in order to understand the effects on diffusion barriers and diffusion coefficients due to the presence of interstitial and substitutional Li defects, hydroxide (O–³H) vacancy defect, and of the interactions of ³H with O-vacancies in the radiation damaged Li₂ZrO₃ crystal. We consider several possible diffusion pathways of interstitial and substitutional ³H and its species in a defective supercell and calculate the activation energy barrier profiles. We find that the smallest activation energy barrier is 0.3 eV and corresponding diffusion coefficient at 600 K is 1.93 × 10^–9 m²/s for ³H substitutional diffusion. The smallest ³H interstitial diffusion barrier and diffusion coefficient are found to be 0.34 eV and 3.25 × 10^–9 m²/s. By examining several channels for diffusion, our results show the most likely diffusion mechanism of ³H migration is occurring along the c-direction by exchange of ³H within and between different Li sites. Here, our calculated results reveal that the smallest energy barrier for O³H diffusion is 0.75 eV which is when O³H is diffusing to the O–Li vacancy pair and the corresponding diffusion coefficient is 6.31 × 10^–13 m²/s. In terms of ³H diffusion, the obtained results indicate that the performance of Li₂ZrO₃ could be better than γ-LiAlO₂, a widely used ceramic material in TPBAR for producing ³H.

• Research Organization: National Energy Technology Lab. (NETL), Pittsburgh, PA (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA)
• OSTI ID: 1573894
• Journal Information: Journal of Physical Chemistry. C, Journal Name: Journal of Physical Chemistry. C Journal Issue: 50 Vol. 122; ISSN 1932-7447
• Publisher: American Chemical Society
• Country of Publication: United States
• Language: English

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