Tritium and helium-3 release from 304L and 21-6-9 stainless steels

Simultaneous 3He and tritium release measurements during linear ramp and isothermal annealing have been made on selections of 304L and 21-6-9 stainless steel tensile bars. Similar results were obtained from both stainless steels during linear ramp thermal desorption. The tritium release was found to smoothly increase with temperature until the sample was depleted, as expected for simple diffusion. In contrast, the amount of 3He released by 9000K was only a small fraction of the total generated from over 5 years of tritium decay. The 3He release data from linear ramp thermal desorption and from isothermal anneals also indicate that the transport of this isotope is complex, and is likely dominated by trapping processes. Samples stored at approx. 900K for several weeks and subsequently annealed began releasing 3He at approx. 1900K. The release fraction below room temperature compared to the amount generated during low temperature aging, however, was also low. Thus, even though the 3He is mobile, with significant transport occurring below room temperature, most is retained and may be a factor in material degradation