Annihilation kinetics of irradiation defects in promising tritium breeding pebbles

Abstract

Lithium-based tritium breeding materials will be adopted to produce tritium in the D-T fusion reactor. Li2TiO3 and Li4SiO4 pebbles have been proposed as candidates in water-cooled ceramic breeder blanket (WCCB) and helium-cooled ceramic breeder blanket (HCCB) respectively. Biphasic ceramics of core–shell Li2TiO3-Li4SiO4 have been considered as advanced breeding materials due to combining the superiority of Li2TiO3 and Li4SiO4. The defects will be introduced into tritium breeders in the operation of fusion reactor. They have important effects on tritium release. It is necessary to carry out the experiment on irradiation defects evolution. The annihilation kinetics of defects induced by γ-ray irradiation were investigated. Fluka and Flair were used to calculate the DPA (displacement per atom) of these irradiated pebbles. EPR (Electron Paramagnetic Resonance) characterization and EasySpin simulation were adopted to analyze the evolution and annihilation kinetics processes of irradiation defects. The concentration of defects decreased as the annealing temperature increased. There were still a certain amount of defects in Li4SiO4 and Li2TiO3-Li4SiO4 when the defects in Li2TiO3 disappeared by annealing. Li2TiO3 pebbles have a better irradiation stability than that of Li4SiO4 pebbles. According to the results of EasySpin simulation, the defect concentration of E’-center and O-related was obtained respectively. The kinetics parameters for the defects of E’-center and O-related center in Li2TiO3 and Li4SiO4 were acquired. The evolution behavior of Ti3+ in core–shell Li2TiO3-Li4SiO4 contributes to the recovery of defects. The correlation between annihilation of irradiation defects and tritium release was discussed. The anti-irradiation damage stability of three kinds of ceramic breeders were evaluated. This work carries out the research on the defect kinetics of the new core–shell structure tritium breeder. Meanwhile, a comprehensive comparison of the annihilation properties of three promising breeders has been made. Li2TiO3 pebbles present excellent tritium release performance due to higher annihilation rate constant. Compared the performances of these breeder pebbles, Li2TiO3 plays a positive role in irradiation tolerance and tritium release performance, and Li4SiO4 has higher lithium density which benefit for tritium production.

Keywords

• Tritium breeder pebble
• Fluka
• Annihilation kinetics
• Tritium release
• Easyspin simulation