LIBRETTO-3: Modelling tritium extraction/permeation and evaluation of permeation barriers under irradiation

Permeation barriers are required in order to limit the size and cost of the detritiation plants for future fusion reactor blankets of the water-cooled Pb-17Li type. The LIBRETTO irradiations were performed to evaluate the efficiency of permeation barriers under high flux reactor (HFR) conditions. Tritium extraction and permeation characteristics from Pb-17Li under variable temperatures 553-723 K, H-2 doping (0-1 vol%) and purge gas flow rates 20-100 sec/min were tested in LIBRETTO-3. An external TIC coating, an internal (TiC + Al2O3), both produced by chemical vapour deposition (CVD), and an internal Al2O3 produced by pack cementation (PC) on AISI 316L steel were tested as permeation barriers. The release mechanisms, experimental uncertainties and method for permeation barriers qualification are presented. As a result permeation reduction factors (PRF) at 0.1 dpa of 17 and 34 were obtained for the CVD-Al2O3 at 498 K and for the PC-Al2O3 at 508 K, respectively. These values were confirmed by a residence time analysis and are higher than in a preliminary analysis [1].