Retention behavior of hydrogen isotopes in boron film deposited on SS-316 for LHD first wall

The chemical states and the deuterium retention of boron films deposited on type 316 stainless steel used as first wall of LHD, which contained 52% oxygen, were studied by means of XPS and TDS. The high oxygen concentration in the boron film could be attributed to oxygen in the surface oxide layer of the stainless steel. The major chemical state of boron with 52% oxygen concentration was B2O3. The B2O3 structure was decomposed to B–B and B–O bonds by the energetic deuterium irradiation. It was found that the deuterium could remain in boron films under operation temperature in the first wall of LHD. The deuterium retention in the boron film deposited on SS was smaller compared to that in the boron film deposited on silicon substrate with 36% oxygen concentration. As the oxygen concentration in boron films increased, the amount of sputtered oxygen was clearly increased, indicating that more heavy water was formed by reacting with implanted deuterium and released, resulting in the smaller deuterium retention in the boron films. The knowledge for the tritium retention in boron films which cannot remove in the operation temperature and the release of tritiated water should be required for the D–D discharge in LHD.