Irradiation effects and hydrogen behavior in H2+ and He+ implanted γ-LiAlO2 single crystals

Abstract

Gamma-phase lithium aluminate (-LiAlO 2 ) is a breeder material for tritium, a necessary substance for strategic stockpile and fusion power systems. A fundamental study of structural evolution and tritium diffusion in -LiAlO 2 under displacive irradiation is needed to fully assess the material performance. This study utilizes ion implantation of protium (surrogate for tritium) and helium in -LiAlO 2 single crystals at elevated temperatures to emulate the irradiation effects. The results show that at 573 K there are two distinct disorder saturation stages to 1 dpa without full amorphization; overlapping implantation of H 2 + and He + ions suggests possible formation of gas bubbles. For irradiation to 10 21 H + /m 2 (0.36 dpa at peak) at 773 K, amorphization occurs at surface with H diffusion and dramatic Li loss; the microstructure contains bubbles and cubic LiAl 5 O 8 precipitates with sizes up to 200 nm or larger. In addition, significant H diffusion and release are observed during thermal annealing.

Role of interfaces in damage process of irradiated lithium aluminate nanocrystals

“…Nevertheless, the implanted ions increase Li local concentration and may lead to the formation of Li 2 O phase. In our previous study, amorphization was accompanied by chemical species separation into Li‐rich region and Al–O rich region which may lead to the formation of Li 2 O and LiAl 5 O 8 , respectively, as observed experimentally …”

“…Following the ion irradiation experiment, our simulations are performed at 573 K. The system is initially equilibrated at 573 K for 0.1 ns using an adaptive time step with a maximum ion displacement of 0.02 Å per step. The basal dimensions were relaxed during the equilibration to achieve zero external pressure.…”

“…These fluxes are ten orders of magnitude higher than a typical flux in ion irradiation experiment. The beam ions are directed at a 60° angle from the surface normal following the experiment . The azimuthal direction of each incident Li is random.…”

“…The effect of grain boundaries on the displacement damage is demonstrated in recent 40‐keV H + ion irradiation experiments on γ‐LiAlO 2 single crystals and polycrystals . The experimental data at a fluence of 10 17 H + /cm 2 show that for temperatures T < 473 K, Li depth profiles remain relatively flat for both cases, however, at 573 K, the polycrystals exhibit a valley (Li‐depleted), while the single crystals remain relatively flat.…”

Tritium Diffusion Pathways in γ-LiAlO2 Pellets Used in TPBAR: A First-Principles Density Functional Theory Investigation

“…It naturally occurs in an amount of around 7% in Li-containing ceramics such as γ-LiAlO 2 with the rest being 7 Li. The 6 Li-enriched γ-LiAlO 2 ( 6 Li enrichment in the 25–30% range) ceramics are used in the form of annular pellets and located in between the zircaloy-4 linear and nickel-plated zircaloy-4 tritium getter in tritium-producing burnable absorber rods (TPBARs). ,, When irradiated in a pressurized water reactor (PWR), the 6 Li absorbs neutrons, simulating the nuclear characteristics of a burnable absorber rod, and produces 3 H along with alpha particles and large amount of energy. The reaction is given as 3 6 Li + n → 1 3 H + α + 4.8 MeV.…”