Divertor repair and replacement is classified as a Remote Handling Class 1 operation, which means that its duration must be minimised and its feasibility shown before construction.

Divertor maintenance includes:

• replacing and refurbishing all components 3 times during the first 10 years of operation and about 5 times overall;
• replacing and refurbishing 16 single faulty components during the machine life;
• positioning the high heat flux components so the maximum step between those on adjacent cassettes would be under 4 mm and so that the maximum variation around the whole torus would be within + 10 mm.
• locking and securing the supports, making water pipe connections, assembling electrical connectors, and handling port plugs.
• replacing all cassettes in less than 6 months and replacing a single cassette in under 8 weeks.

The L-7 project is devoted to demonstrating that these operations are feasible and can be done in the required time.

Two test facilities - the Divertor Test Platform and the Divertor Refurbishment Platform - have been set up at the ENEA Research Centre of Brasimone, near Bologna (Italy).The Divertor Test Platform is used to simulate in full scale all handling operations inside the Vacuum Vessel, including removal/replacement through vessel ports.

The key elements of the maintenance procedure are shown above:

• radial insertion of the cassette from the chamber using radial movers;
• toroidal manoeuvring using toroidal mover;
• lowering of cassette into position on bi-directional forks;
• remote attachment to rail;

Specialised movers ("cassette carriers") are used to install the central casssettes and the two adjacent ones, as shown below.

Tests on the DTP confirm the maintenance concept, its integration inside the vessel, accuracy of cassette positioning, adequacy of nominal gaps and tolerances, and payload capabilities. Certain improvements have been investigated to reduce costs and to implement lessons learnt in the early tests to improve man-machine interface, sensors, and time, as well as to improve sliding components and to investigate rescue scenarios if components become jammed.

In initial tests, local controllers situated close to the equipment were used for operation. This capability was later transferred to the control room allowing fully remote operation.

The cassette toroidal mover had been shown capable of tolerating misalignments between itself and the cassettes of up to 10 mm toroidally. It has been shown capable of tolerating 2mm steps or gaps between rail sectors.

Realistic estimates of intervention time are now possible. The total in-vessel time (i.e. excluding pipe cutting/welding, port handling and cask operations) to install 15 cassettes (one quarter of the divertor in the previous ITER design) is 32 hours.

A realtime 3D computer simulation model of the DTP has been created. This has been integrated into the DTP supervisory system and has been successfully tested.

The Divertor Refurbishment Platform is for simulating the most critical operations to be undertaken in the Hot Cell. The assembly and disassembly of high heat flux components (HHFCs) is simulated with prototype tools. Only those parts of the mock-up which are critical for HHFC mounting have been machined accurately. Tests show that the remote measurement system can be operated accurately enough (0.01 mm) that components can be correctly machined to fit. A target has been installed on the cassette with the required accuracy, and proceedures have been streamlined to shorten the time taken.

Divertor Refurbishment Platform

The L-7 project is jointly performed by the European and Japanese Home Teams. Project management is the joint responsibility of the EU Home Team and the Garching Joint Work Site.