Deuterium removal during thermo-oxidation of Be-containing codeposits from JET divertor tiles

Abstract

This study focuses on the removal of trapped D from thick codeposits on JET divertor tiles via thermo-oxidation. The tiles were removed from the JET Mark II Gas Box divertor after the 1998–2001 campaign. These codeposits have Be concentrations of up to ∼60% Be/(Be + C) and their thicknesses range from 10 to 270 µm. Laser thermal desorption spectroscopy was used to determine the D removal rates and final remaining D concentrations following oxidation. Estimates of the carbon removed during oxidation were obtained from mass-loss measurements. The initial rate of D removal was found to be much higher for the thick codeposits of this study than for the previously studied codeposits with thicknesses in the range 1–5 µm (from TFTR, DIII-D and JET). This is despite the large Be concentrations. For oxidation performed at 623 K (350 °C) and 21 kPa (160 Torr) O2 pressure the initial D removal rates were found to increase linearly with increasing ‘inherent’ D content; about 50% of the inherent D was removed from all specimens in the first 15 min—independent of Be content and codeposit thickness. Following 8 h of oxidation, the fraction of D removed was >85% for all specimens, again, independent of Be content and thickness.