Tritium diffusion and formation in the bulk and defective surface of γ-LiAlO2 pellets: First-principles investigation
- NETL
- NETL Site Support Contractor, National Energy Technology Laboratory
- Pacific Northwest National Laboratory (PNNL)
In tritium-producing burnable absorber rods (TPBAR), γ-LiAlO2 is used in the form of an annular ceramic pellet enriched with the 6Li isotope. When irradiated in a pressurized water reactor (PWR), the <sup>6</sup>Li pellets absorb neutrons and produce tritium (<sup>3</sup>H) through <sup>6</sup>Li + n <sup>3</sup>H + α. The 3H chemically reacts with the metal getter where it is captured and leads to formation of a metal hydride. For TPBARs to enable effective tritium production in PWRs, we investigated the <sup>3</sup>H diffusion pathways in the bulk and surface of γ-LiAlO<sub>2</sub> with different concentrations of lithium defects. The calculated results for bulk and low-index surfaces, thermal conductivity, 3H activation energy barriers, and the 3H diffusion coefficients in γ-LiAlO<sub>2</sub> are in good agreement with the available experimental values. In the bulk, our results show that the smallest activation energy barrier is 0.63 eV for substitutional <sup>3</sup>H diffusion with a diffusion coefficient of 3.25x10<sup>-12</sup> m<sup>2</sup>/s. After <sup>3</sup>H diffused from bulk to the surface, it could form different species (such as <sup>3</sup>H<sub>2</sub>, <sup>3</sup>H<sub>2</sub>O, C<sup>3</sup>H<sub>4</sub>) depending on the surface structure, vacancy types and the impurity carbon. Our results indicate that the <sup>3</sup>H<sub>2</sub> is the main product from γ-LiAlO<sub>2</sub> pellets. As the number of V<sub>Li</sub> vacancies and <sup>3</sup>H atoms increases under irradiation (<sup>3</sup>H-rich condition), <sup>3</sup>H<sub>2</sub>O release could increase from the surface of γ-LiAlO<sub>2</sub> pellets.
- Research Organization:
- National Energy Technology Laboratory (NETL), Pittsburgh, PA, Morgantown, WV, and Albany, OR (United States)
- Sponsoring Organization:
- USDOE Office of Fossil Energy (FE)
- DOE Contract Number:
- FWP- WFO-2816053 Tritium Science - FY18
- OSTI ID:
- 1854572
- Resource Relation:
- Conference: Conference Name: APS March Meeting (Virtual) Location: N/A, N/A, United States Start Date: 3/14/2022 12:00:00 AM End Date: 3/18/2022 12:00:00 AM
- Country of Publication:
- United States
- Language:
- English
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