The Impact of Acid Treatments and Electropolishing Stainless-Steel Surfaces on Tritium Inventories

The concentration of tritium in the adsorbed water layer on stainless-steel type 316 is notably higher than that present in the metal lattice. The absorbed waters play a key role in the migration of tritium into the metal. In this work, stainless-steel (type 316) surfaces were subjected to various pretreatments designed to alter the surface in order to probe the relation between surface conditions and total tritium inventories. These pretreatments included electropolishing and soaking in nitric-acid baths. Stainless-steel samples were loaded with tritium by exposure to a deuterium–tritium gas mixture at 25°C for 24 h. Total tritium inventories were measured using temperature-programmed desorption. The thermal desorption data show a reduction of 65% in total tritium inventory by electropolishing stainless-steel surfaces as compared to unmodified samples. It is also shown that treating the surfaces with nitric acid resulted in an increase in the tritium content by ~200%.