Annihilation kinetics of irradiation defects in promising tritium breeding pebbles

Abstract

• γ-Ray irradiation mainly introduces E′-center and O-related (O - -center, O 2 - center et.al) defects in Li 2 TiO 3 , Li 4 SiO 4 and Li 2 TiO 3 -Li 4 SiO 4 pebbles. • Isochronal and isothermal annealing experiment were carried out to illustrate the annihilation kinetics of different breeding pebbles. • Li 2 TiO 3 pebbles have a better irradiation stability than Li 4 SiO 4 pebbles. Lithium-based tritium breeding materials will be adopted to produce tritium in the D-T fusion reactor. Li 2 TiO 3 and Li 4 SiO 4 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 Li 2 TiO 3 -Li 4 SiO 4 have been considered as advanced breeding materials due to combining the superiority of Li 2 TiO 3 and Li 4 SiO 4 . 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 Li 4 SiO 4 and Li 2 TiO 3 -Li 4 SiO 4 when the defects in Li 2 TiO 3 disappeared by annealing. Li 2 TiO 3 pebbles have a better irradiation stability than that of Li 4 SiO 4 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 Li 2 TiO 3 and Li 4 SiO 4 were acquired. The evolution behavior of Ti 3+ in core–shell Li 2 TiO 3 -Li 4 SiO 4 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. Li 2 TiO 3 pebbles present excellent tritium release performance due to higher annihilation rate constant. Compared the performances of these breeder pebbles, Li 2 TiO 3 plays a positive role in irradiation tolerance and tritium release performance, and Li 4 SiO 4 has higher lithium density which benefit for tritium production.