Abstract
Lithium metatitanate, Li2TiO3, is a leading candidate for application as a tritium breeding material in a future fusion reactor. Following transmutation of lithium, the tritium must escape the crystal in order to be extracted for use in the fusion plasma. The rate-limiting step to release tritium from the Li2TiO3 pebbles is diffusion through the crystal grains. In this work, the activation barriers for tritium diffusion have been calculated using density functional theory. The results show that tritium can diffuse as an interstitial with a barrier of 0.52 eV. However, when a tritium ion becomes bound to a lithium vacancy defect, the energy required to either detrap the tritium from the vacancy or for the cluster to diffuse increases to >1 eV. Overall, these results suggest that the introduction of lithium vacancies due to Li burn-up may lead to an increase in tritium retention in the pebbles.
Highlights
Future fusion reactors will employ the reaction between deuterium and tritium to release energy for electricity generation
Because there is very limited naturally occurring tritium, it is expedient to generate it in situ from the transmutation of lithium using the high-energy neutron ejected from the D−T reaction
Because of the inability to completely surround the plasma with the blanket and the permeation of tritium into other reactor components, a tritium breeding ratio (TBR) greater than 1.1 is necessary.[2]
Summary
Future fusion reactors will employ the reaction between deuterium and tritium to release energy for electricity generation. Because there is very limited naturally occurring tritium, it is expedient to generate it in situ from the transmutation of lithium using the high-energy neutron ejected from the D−T reaction. This will be done by surrounding the plasma chamber with a blanket region containing a lithium breeder material. Because of the inability to completely surround the plasma with the blanket and the permeation of tritium into other reactor components, a tritium breeding ratio (TBR) greater than 1.1 is necessary.[2] In the case of a solid breeder, the high-energy neutrons will penetrate the pebbles, leading to tritium being generated throughout the ceramic matrix. The tritium will undergo isotope exchange reactions with hydrogen in the He purge gas before being recovered
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