(489e) Fundamental Studies of Tritium Diffusivity in Carbon Doped Defective ?-LiAlO2 Pellets
AIChE Annual Meeting
2019
2019 AIChE Annual Meeting
Nuclear Engineering Division
Theory, Modeling, and Simulation of Nuclear Chemical Processes I
Wednesday, November 13, 2019 - 9:28am to 9:50am
Fundamental
Studies of Tritium Diffusivity in Carbon Doped Defective γ-LiAlO2
Pellets Hari P. Paudel1, David J. Senor2,
Yuhua Duan1 1
National
Energy Technology Laboratory, United States Department of Energy, Pittsburgh,
Pennsylvania 15236, USA 2 Pacific
Northwest National Laboratory, Richland, Washington 99354, USA Abstract: γ-LiAlO2
is a ceramic material with superior thermo-physical and thermo-chemical
properties, and is highly compatible with other materials being used in the
form of annular pellets in tritium-producing burnable absorber rods (TPBARs) to
produce tritium (3T) by thermal
neutron irradiation of 6Li. In addition to that γ-LiAlO2
has an excellent irradiation behavior at high temperature, and is more
swelling resistant than many other Li rich materials1,2. The 3H
diffusion and recovery processes have been studied experimentally in ceramic
breeding materials irradiated with neutron beams by Okuno and Kudo3,4.
It was revealed that the tritium produced in the ceramic materials (Li2O,
γ-LiAlO2, Li2SiO3, Li4SiO4,
Li2ZrO3, Li8ZrO6) irradiated with
neutron beams was released mainly in the chemical form of tritiated water (HTO)
when heated in vacuum4. The step before release of 3H to
gas gap in reactor in the form of HTO involves an atomic migration of 3H
through grains of radiation damaged material in bulk. The
study of Li diffusivity in Li containing ceramics such as γ-LiAlO2
and Li2ZrO3 has also been a subject of interest in Li-ion
battery and solid oxide fuel cells. In the past, by using NMR and dc conductivity
measurements in γ- LiAlO2, it was found that the Li diffusion
coefficient is in the range 10-20 to 10-13 m2/s
in the temperature range of 400 K to 1000 K5. In the same
experiment, the Li activation energy was found to vary between 0.74 to 1.14 eV.
By calculating several different diffusion pathways, Paudel et al show
that the smallest activation energy barrier for 3T in pure γ-LiAlO2
is 0.63 eV for substitutional tritium diffusion and corresponding diffusion
coefficient is 3.25x10-12 m2/s6. The experimental observation in a polycrystalline
γ-LiAlO2irradiated
with both 4He+ and 1H+ ions reveals
that there is a formation of isolated elementary voids along with other phases
of lithium and aluminate (LiH and LiAl5O8)7.
These elementary voids are believed to trap diffusing entities (Li and 3T)
and hinder their diffusivities at the elevated temperatures. Identifying trapping
sites of light elements like Li and 3T requires image resolution in
atomic scale, and so far it is not clearly understood experimentally. Here we
present theoretical studies based on the first principles density functional
theory to calculate the formation of voids and their influences on the
diffusion barriers of 3T. In particular, we calculate different
pathways of 3T migration in presence of voids and find a minimum
energy barrier for diffusion in bulk. We also examine vacancy-vacancy
interaction energy to understand the properties of voids., We find that the
interaction energy is 0.12 eV between two 1st NN VLi. It
decreases monotonically as distance between them increases. In experiment, it
has also been reported that there is presence of carbon impurities in defective
γ-LiAlO2. We calculate
the formation of C-impurity and the diffusion barrier in C-doped γ-LiAlO2,
and compare the barrier energies with the case of pure γ-LiAlO2.
Our calculation shows that the smallest diffusion barrier for 3T is found to be
0.98 eV in a C-doped γ-LiAlO2
which is 0.35 eV higher than that in pure γ-LiAlO2.
Studies of Tritium Diffusivity in Carbon Doped Defective γ-LiAlO2
Pellets Hari P. Paudel1, David J. Senor2,
Yuhua Duan1 1
National
Energy Technology Laboratory, United States Department of Energy, Pittsburgh,
Pennsylvania 15236, USA 2 Pacific
Northwest National Laboratory, Richland, Washington 99354, USA Abstract: γ-LiAlO2
is a ceramic material with superior thermo-physical and thermo-chemical
properties, and is highly compatible with other materials being used in the
form of annular pellets in tritium-producing burnable absorber rods (TPBARs) to
produce tritium (3T) by thermal
neutron irradiation of 6Li. In addition to that γ-LiAlO2
has an excellent irradiation behavior at high temperature, and is more
swelling resistant than many other Li rich materials1,2. The 3H
diffusion and recovery processes have been studied experimentally in ceramic
breeding materials irradiated with neutron beams by Okuno and Kudo3,4.
It was revealed that the tritium produced in the ceramic materials (Li2O,
γ-LiAlO2, Li2SiO3, Li4SiO4,
Li2ZrO3, Li8ZrO6) irradiated with
neutron beams was released mainly in the chemical form of tritiated water (HTO)
when heated in vacuum4. The step before release of 3H to
gas gap in reactor in the form of HTO involves an atomic migration of 3H
through grains of radiation damaged material in bulk. The
study of Li diffusivity in Li containing ceramics such as γ-LiAlO2
and Li2ZrO3 has also been a subject of interest in Li-ion
battery and solid oxide fuel cells. In the past, by using NMR and dc conductivity
measurements in γ- LiAlO2, it was found that the Li diffusion
coefficient is in the range 10-20 to 10-13 m2/s
in the temperature range of 400 K to 1000 K5. In the same
experiment, the Li activation energy was found to vary between 0.74 to 1.14 eV.
By calculating several different diffusion pathways, Paudel et al show
that the smallest activation energy barrier for 3T in pure γ-LiAlO2
is 0.63 eV for substitutional tritium diffusion and corresponding diffusion
coefficient is 3.25x10-12 m2/s6. The experimental observation in a polycrystalline
γ-LiAlO2irradiated
with both 4He+ and 1H+ ions reveals
that there is a formation of isolated elementary voids along with other phases
of lithium and aluminate (LiH and LiAl5O8)7.
These elementary voids are believed to trap diffusing entities (Li and 3T)
and hinder their diffusivities at the elevated temperatures. Identifying trapping
sites of light elements like Li and 3T requires image resolution in
atomic scale, and so far it is not clearly understood experimentally. Here we
present theoretical studies based on the first principles density functional
theory to calculate the formation of voids and their influences on the
diffusion barriers of 3T. In particular, we calculate different
pathways of 3T migration in presence of voids and find a minimum
energy barrier for diffusion in bulk. We also examine vacancy-vacancy
interaction energy to understand the properties of voids., We find that the
interaction energy is 0.12 eV between two 1st NN VLi. It
decreases monotonically as distance between them increases. In experiment, it
has also been reported that there is presence of carbon impurities in defective
γ-LiAlO2. We calculate
the formation of C-impurity and the diffusion barrier in C-doped γ-LiAlO2,
and compare the barrier energies with the case of pure γ-LiAlO2.
Our calculation shows that the smallest diffusion barrier for 3T is found to be
0.98 eV in a C-doped γ-LiAlO2
which is 0.35 eV higher than that in pure γ-LiAlO2.
Figure:
Substitutional Tritium diffusion in presence of interestitial C impurity.
References
1. Cao,
H. et al., Solid State Ionics 2005, 176, 911-914
2. Li,
L. J. et al, J. Mater. Chem. A 2015,
3, 894-904
3. Okuno
K. et al., J. Nucl. Mater. 2001,
299, 242-249
4. Okuno
K. et al., Fusion Eng. Des. 1989, 8, 355-358
5. Indris,
S. et al., J. Phys. Chem. C 2012,
116, 14243-14247
6. Paudel,
H. P. et al., J. Phys. Chem. C 2018, 122, 9755
7. Jiang,
W. et al., J. Nucl. Mater. 2018, 511, 1