Design of Safety Important Feedthroughs for ITER HNB Injectors

Safety important feedthroughs will realise the first vacuum boundary of the ITER Neutral Beam injectors providing the transfer of electrical power, mechanical motion, and measurement signals. The designs of the feedthroughs are based on previous experience from similar components procured for fusion applications. They are developed to satisfy vacuum leak tightness, nuclear radiation, remote handling maintenance, quality, and specific requirements for each type of feedthrough. The electrical power feedthrough for the residual ion dump is designed to transfer up to 60 A at 30 kV. The actuator feedthrough for the calorimeter movements will transfers the linear motion of a shaft into the vacuum vessel via a replaceable bellows unit. The thermocouple feedthrough is designed to transfer 126 pairs of cables and will provide the electrostatic shielding from electromagnetic interference. All feedthroughs have double vacuum barriers with a monitored interspace to enable early detection in case of a leak. A faulty feedthrough can therefore be replaced in a controlled way without a compete loss of confinement. The vacuum leak tightness is achieved either with double metallic seals or by butt and lip welds compatible with the assembly sequence and with welding examination requirements for bellows and box structures. The feedthrough design was verified by analysis simulating combinations of pressure, thermal, structural, electro-magnetic, nuclear radiation, and seismic loads as specified for the ITER operation. The design was complemented by assembly verifications and proof testing conditions to be specified for manufacturing.