Recent results on vacuum pumping and fuel clean-up

Abstract

Considerable R&D effort has gone into the development of a Torus Exhaust Vacuum Pumping System over the past years. The selected primary pump is of cycling type with discontinuous regeneration, solid cryosorbent for helium pumping and no fuel separation. The pump includes a throttle/regeneration valve to maintain the divertor pressure, minimize the thermal load on the pump and permit regeneration. Modelling of various torus cryopump configurations has been carried out and a research program aimed at developing a primary torus cryopump with rapid regeneration cycles is in progress. Panel tests with tritium will provide additional data required for ITER design. The design, fabrication and demonstration of a model cryopump with integral inlet valve is in progress. Experimental work and modelling to develop a high speed pumping system for the neutral beam injector is under way. Practical experience under ITER relevant conditions and in the presence of tritium has accumulated on the performance of oil-free pumps in various tritium laboratories. Recent world-wide developments in the field of fuel clean-up have been impressive. Several concepts based on palladium/silver diffusors combined with catalytic as well as with electrochemical process steps have the potential to achieve the high overall tritium decontamination factors and low tritium inventory levels required by ITER. Basic research activities aimed at characterizing and optimizing the envisioned essential components for the various ITER fuel clean-up concepts are in progress. Tests with an industrially manufactured facility of technical scale employing realistic concentrations of tritium and using an advanced operation and safety concept have been performed. Optimization of process components with respect to performance, operability and safety criteria is proceeding in parallel with integrated loop tests. Endurance tests to demonstrate complete processes with tritium are in preparation in several laboratories. Basic research aimed at developing a process for the recovery of tritium from the helium glow discharge cleaning exhaust stream is under way. The routine operation with tritium of large civilian research laboratories under conditions specific to the respective sites will contribute significantly to a realistic design of the ITER Tritium Plant. For the operation of the Tritium Plant and tritium accountancy much effort has gone into the improvement of known analytical techniques and the further development of calorimetry.