Distribution of Tritium in the Near Surface of Type 316 Stainless Steel

The distribution of tritium in the near surface of Type 316 stainless steel has been measured using a combination of a zinc chloride (ZnCl2) wash and acid etching with diluted aqua regia. This method improves upon etching measurements reported in the literature: Results show depth resolutions of ~10?nm using the diluted aqua regia. The ZnCl2 wash results show very high surface concentration (~1.5???10(13) Bq/cm(3)), which decreases by a factor of 10(6) after etching to a depth of ~10??m. Further, the tritium concentrations in the near surface (<10??m) of unmodified stainless steel samples do not change significantly over the course of 233?days, which indicates a quasi-equilibrium state has been reached. Tritium migration to the surface from the subsurface region was measured by etching a sample and then storing it in air for 2 to 4?days. After storing in air, the surface concentrations increased a thousandfold and rapidly decreased to base levels after etching an additional ~2??m. These measurements indicate that perturbing the quasi-equilibrium concentration profile results in tritium migration to the surface in order to reestablish the prior equilibrium state.