Abstract
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 × 1013 Bq/cm3), which decreases by a factor of 106 after etching to a depth of ~10 μm. Further, the tritium concentrations in the near surface (<10 μm) 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 μm. 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.
Acknowledgments
This material is based upon work supported by the U.S. Department of Energy National Nuclear Security Administration under award number DE-NA0003856, the University of Rochester, and the New York State Energy Research and Development Authority.