Tritium Migration to the Surfaces of Type 316 Stainless Steel; Aluminum 6061; and Oxygen-Free, High-Conductivity Copper

The migration of tritium to the surfaces of Aluminum 6061; oxygen-free, high-conductivity copper; and Type 316 stainless steel from the bulk metal was studied using low-pressure Tonks-Langmuir argon plasma. The plasma is shown to be effective at removing tritium from metal surfaces in a controlled manner. Tritium is removed in decreasing quantities with successive plasma exposures, which suggests a depletion of the surface and near-surface-tritium inventories.

A diffusion model was developed to predict tritium migration from the bulk and its accumulation in the water layers present on the metal surface. The model reproduces the rate of tritium regrowth on the surface for all three metals and can be used to calculate the triton solubility in the water layers present on metal surfaces. The ratio of surface-to-bulk solubilities at the water layer–bulk metal interface uniquely determines the concentration ratio between these two media. Removing the tritium-rich water layers induces tritium to migrate from the bulk to the surface. This process is driven by a concentration gradient that develops in the bulk because of the perturbation on the surface.