(305c) Stability and Interactions of Point Defects in Lithium Metal Oxides for the Tritium-Producing Burnable Absorber Rod Applications
AIChE Annual Meeting
Tuesday, October 30, 2018 - 8:50am to 9:15am
Energetics in Lithium Metal Oxides for Tritium-Producing Burnable Absorber Rod
Lee1, Jamie Holber1, Hari P.
Paudel1, Dan C. Sorescu1, and Yuhua
Energy Technology Laboratory, 626 Cochrans Mill Road,
P.O. Box 10940, Pittsburgh, Pennsylvania 15236-0940, USA
such as γ-LiAlO2, Li2TiO3, and Li2ZrO3,
are candidate systems for their suitability as blanket materials in
tritium-producing burnable absorber rods (TPBARs). After adsorbing neutrons, 6Li
is readily converted to tritium through
reaction . The oxide defects
and structural disorder may enhance the diffusion of Li and tritium species
within TPBAR materials. Previous experimental results have indicated that
interactions between tritium and irradiation-induced defects could play a key
role in the observed tritium solubility and diffusivity and overall can modify
the tritium release from TPBAR materials [2,3].
Furthermore, previous theoretical studies in bulk Li2O and Li2TiO3
[4-6] have suggested that both Li and O vacancies can act as trapping sites for
this work, the phase stability and defects energetics of LixMyOz
(M=Al, Ti, and Zr) materials are investigated using density functional theory
(DFT) calculations and ab initio thermodynamic
analysis. Theoretical investigations were performed for several types of
charged defects including vacancies, interstitials, antisite defects, and 3H
substitutional defects to identify the trends of the point defects stability
under TPBAR operating temperature and oxygen partial pressure conditions [7,8]. The interplay between defects stability, defects
interactions, the change of the environmental chemical potentials, and the
intrinsic Fermi energy level under the TPBAR operating conditions are
discussed. As shown in the Figure 1 below, our results suggest that
interactions between the tritium and the point defects are dependent on the
electron chemical potential across the band gap, i.e. the Fermi energy
level. By considering the intrinsic Fermi level position for a range of
external conditions, i.e. P(O2)=10-5atm at T=1000K to P(O2)=10-25atm at T=1000K, the results obtained suggest that
γ-LiAlO2 phase exhibits stronger interactions between the 3H
interstitial and the VLi, VO,
and Oint defects than Li2TiO3
and Li2ZrO3 materials, indicating a higher tendency to
trap 3H at these point defects  and correspondingly a lower
efficiency for tritium recovery in TPBARs.
the three TPBARmaterials investigated, i.e., Li2TiO3,
Li2ZrO3, and γ-LiAlO2, our results
indicate that the point defect formation energies are higher
in γ-LiAlO2 than in the other
two materials. The increased defect stability in γ-LiAlO2 correlates also with the experimental
tritium/hydrogen diffusivities which are the slowest in this material. At the
same time, the higher point defect formation energies observed in γ-LiAlO2
indicate a greater stability of this material with the possibility to better withstand the long-term irradiation at high
temperatures in a reactor. Our theoretical results provide thermodynamic
guidance for the factors governing the tritium transport properties , point
defect energetics and the phase stability in LixMyOz
(M=Al, Ti, and Zr) systems under TPBAR operating chemical potential conditions
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 Lee, Y.-L; Holber, J.; Paudel, H. P..; Sorescu, D. C.;
Sensor, D.; Duan, Y., Density Functional Theory
Study of the Point Defect Properties for the γ-LiAlO2, Li2ZrO3,
and Li2TiO3 Materials, (2018) to be submitted.
 Broberg, D., et al., PyCDT: A
Python toolkit for modeling point defects in semiconductors and insulators. Computer Physics Communications, 2018. 226, p.
 Paudel, H. P., Lee, Y. -L., Senor, D. L., Duan, Y., Tritium Diffusion Pathways in γ-LiAlO2
Pellets Used in TPBAR: a first-principles density functional theory
investigation, Journal of Physical Chemistry C (2018) revision submitted.
 Paudel, H. P., Lee, Y.-L., Holber,
J., Sorescu, D. C., Duan,
Y., Fundamental Studies of Tritium Solubility and Diffusivity in LiAlO2
and Lithium Zirconates Pellets Used in TPBAR,
Tritium Science Program FY17 Report, DOE/NETL-PUB-21464, Nov. 2017
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