Experimental and computational studies on tritium permeation mechanism in erbium oxide

A tritium permeation barrier (TPB) is much required in fusion blankets to reduce the loss of fuel and minimize radiological hazard. However, the detailed mechanism of tritium permeation through TPB coatings has not yet been clarified because of their complicated crystal structures. To understand the microscopic mechanism, we have not only prepared and characterized nanostructured ceramic Er2O3 thin films, but also studied the energetics and mobility of interstitial deuterium in cubic bulk Er2O3 using ab initio density-functional calculations. The estimated diffusion activation energy (Ea) of interstitial deuterium is somewhat higher than the diffusion energy barrier observed experimentally at 873 K. This result shows that grain boundary structures existing in the TPB of Er2O3 significantly lower the diffusion barrier and change the diffusion pathway. Transport of hydrogen and its isotopes through the Er2O3 coatings are likely to be dominated by grain boundaries rather than by grains. (author)