Researchers discover mechanism behind influence of irradiation defects on tritium permeation barrier

Recently, researchers led by Prof. Zhou Haishan from the Institute of Plasma Physics (ASIPP) of the Hefei Institutes of Physical Science (HFIPS) reported their new findings about the influence of irradiation effects on hydrogen permeation through alpha-alumina (α-Al₂O₃) tritium permeation barrier (TPB).

Tritium self-sufficiency is one of the most important issues in the development of nuclear fusion power. It is also one of the top priorities of the Chinese Fusion Engineering Test Reactor (CFETR).

In order to reduce the permeation of tritium as much as possible, a thin coating layer adhered to the outer surface or inner wall of the structural materials in the blanket and auxiliary tritium handling systems, TPB, is suggested. α-Al₂O₃, owing to its good thermal stability, electrical insulation radiation stability and high permeation reduction factor (PRF), is considered to be the most promising TPB material for fusion reactors.

However, many irradiation defects can be produced through the neutrons collision cascade in fusion reactor, which have serious impacts on the effective PRF of α-Al₂O₃.

After exploring the influence of irradiation-induced point defects on the dissolution and diffusion properties of hydrogen (H) in α-Al₂O₃, the team found that the isolated defects can trap multiple H atoms to form H-defect complexes and impede the diffusion process of H, resulting in a higher PRF of α-Al₂O₃ TPB.

Besides, the low migration barrier of OiH-, leading to a higher diffusivity, was considered a possible underlying reason for the low permeation efficiency of α-Al₂O₃ TPBs in irradiation environments.

They also suggested that, as for H permeation prevention, the irradiated α-Al₂O₃ TPB is more effective in a H₂O environment than in a H₂ environment.

Their results can help researchers to understand the transport mechanism of H in irradiated α-Al₂O₃, and provide a reasonable theoretical explanation for experimental results of H permeation in α-Al₂O₃ under irradiation environments in recent years.