Effects of irradiation temperature on tritium retention in stainless steel type 316L

Dependence of irradiation temperature on tritium retention has been studied using stainless steel type 316L (SS316L) as a model sample. A mixture of D₂⁺ and DT⁺ ions was used and two kinds of ion energy, 0.5 and 2.5 keV, were applied. In case of irradiation tests by 0.5 keV, tritium retention decreased with increasing temperature up to 523 K, while above this temperature it contrarily showed an increase tendency. Such a concave change was not observed for irradiation tests at 2.5 keV. The retention was almost same until 400 K, but above this temperature it decreased gradually. It was seen from the analyses by X-ray photoelectron spectroscopy that most of surface was initially covered with the carbon and oxygen species at room temperature. Among metallic elements, constituents such as Fe and Ni were metallic states more than 60 % at room temperature, while metallic chromium atoms were little observed. Both fractions of the metallic chromium and iron atoms in the major base metals of SS316 L increased with an increase in temperature, but metallic nickel atoms relatively decreased. It was suggested, therefore, that real surface states of the irradiation materials play an important role for behavior of tritium retention.