Maintenance of neutral beam injectors for ITER (Japanese proposal)

Concepts and scenarios of maintenance for ITER neutral beam injectors are proposed. Main features of the proposal are as follows: (1) Structures made of concrete are employed to support the weight of the injectors; (2) each injector can be separated into two units: Ion source unit and beamline unit; (3) since the ion source is considered to require frequent maintenance, each ion source unit can be removed independently of the other ion source units, by means of rail-and-truck system; (4) double door concept is adopted in two large gate valves to prevent spreading of the radioactivated contamination; (5) laser welding/cutting technique and shape memory alloy are utilized to ease connection/disconnection of pipes, cables, etc.; (6) if any failure occurrs in an ion source unit or a beamline unit, the unit will be transferred to a hot cell. Then the unit will be disassembled and the failed components will be repaired in the cell. Considering these concepts, maintenance scenarios are worked out for four cases; ion source unit disassembly/assembly, and beamline unit disassembly/assembly. (orig.)