AbstractDependence of tritium release on purge gas chemistry has been studied in the temperature range 350–600°C for a variety of lithium orthosilicate and metazirconate samples (mainly 0.5 mm diameter pebbles) in the TRIDEX series of purged inpile tests. TRIDEX results were found to be in reasonable agreement with previous inpile experiments. Tritium release is remarkably improved by adding small percentages of hydrogen to the helium purge gas and/or by reducing the oxigen partial pressure of the helium purge gas. Similar tritium release behaviour of different charges of spheres prepared from molten orthosilicate demonstrates reproducibility of this fabrication route.