[en] The heterogeneous reaction between oxygen gas and permeating tritium is being studied at the back surface of an oxidized 316-stainless steel tube. The ratio between the reaction products collected at the back surface, tritiated water and molecular tritium, is determined as a function of oxygen level, tritium concentration, protium concentration, flow rate, and temperature. This report describes the results from two sets of runs done at 550⁰C with and without 15 ppm protium in the oxygen/helium gas. At oxygen levels of 1200-2000 ppm, the ratio of tritiated water to molecular tritium was >40, i.e., a 98% conversion. At oxygen levels of 40 ppm, the presence of excess protium in the oxygen/helium resulted in a reduced yield of tritiated water