Tritium diffusion and formation in the bulk and defective surface of γ-LiAlO2 pellets: First-principles investigation

Conference · Fri Mar 11 04:00:00 EST 2022

OSTI ID:1854572

Jia, Ting ^[1]; Paudel, Hari P. ^[2]; Senor, David ^[3]; Duan, Yuhua ^[1]

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1. NETL
2. NETL Site Support Contractor, National Energy Technology Laboratory
3. 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 ⁶Li pellets absorb neutrons and produce tritium (³H) through ⁶Li + n ³H + 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 ³H diffusion pathways in the bulk and surface of γ-LiAlO₂ 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-LiAlO₂ 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 ³H diffusion with a diffusion coefficient of 3.25x10^-12 m²/s. After ³H diffused from bulk to the surface, it could form different species (such as ³H₂, ³H₂O, C³H₄) depending on the surface structure, vacancy types and the impurity carbon. Our results indicate that the ³H₂ is the main product from γ-LiAlO₂ pellets. As the number of V_Li vacancies and ³H atoms increases under irradiation (³H-rich condition), ³H₂O release could increase from the surface of γ-LiAlO₂ 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)
• OSTI ID: 1854572
• Country of Publication: United States
• Language: English