Mechanisms of helium accommodation in lithium metatitanate

• Determination of dominant modes for He accommodation in Li2TiO3.
• Identification of a mechanism by which He can increase tritium diffusivity.

Helium is generated as a by-product of the transmutation of lithium in the breeder blanket region of a fusion reactor. The presence of helium in ceramic breeder materials, such as lithium metatitanate (Li2TiO3), can lead to pressure in the pebble and degradation of mechanical properties as well as influencing tritium retention in the matrix. Here, density functional theory is used to examine the mechanisms of helium accommodation in Li2TiO3 across a range of conditions relevant to a fusion reactor. The results show that the mechanism of helium accommodation depends on the availability of defect trap sites, which itself depends on the stoichiometry of the crystal. It is also shown that helium may displace tritium from lithium vacancy defects and may therefore increase the tritium extraction rate by increasing the fraction of mobile tritium ions.