Catalytic membrane reactors for tritium recovery from tritiated water in the ITER fuel cycle

Palladium and palladium-silver permeators have been obtained by coating por ous ceramic tubes with a thin metal layer. Three coating techniques have be en studied and characterized: chemical electroless deposition (PdAg film th ickness of 10 mum), ion sputtering (about 1 mum) and rolling of thin metal sheets (50 mum). The Pd-ceramic membranes have been used for manufacturing catalytic membrane reactors (CMR) for hydrogen and its isotopes recovering and purifying. These composite membranes and the CMR have been studied and developed for a closed-loop process with reference to the design requiremen ts of the international thermonuclear experimental reactor (ITER) blanket t ritium recovery system in the enhanced performance phase of operation. The membranes and CMR have been tested in a pilot plant equipped with temperatu re, pressure and flow-rate on-line measuring and controlling devices. The c onversion value for the water gas shift reaction in the CMR has been measur ed close to 100% (always above the equilibrium one, 80% at 350 degreesC): t he effect of the membrane is very clear since the reaction is moved towards the products because of the continuous hydrogen separation. The rolled thi n film membranes have separated the hydrogen from other gases with a comple te selectivity and exhibited a slightly larger mass transfer resistance wit h respect to the electroless membranes. Preliminary tests on the sputtered membranes have also been carried out with a promising performance. Consider ations on the use of different palladium alloy in order to improve the perf ormances of the membranes in terms of permeation flux and mechanical streng th, such as palladium/yttrium, are also reported. (C) 2000 Elsevier Science B.V. All rights reserved.