These modules allow the testing of design concepts of tritium breeding high temperature blankets relevant to a future fusion power reactor, and in particular to the next step beyond ITER (DEMO). Several concepts are likely to be tested:

• water-cooled solid breeder (pebble-bed lithium ceramic/Be blankets with ferritic-martensitic steel structures);
• helium-cooled solid breeder (pebble-bed lithium ceramic/Be blankets with ferritic-martensitic steel structure) (EU example);
• self-cooled liquid lithium breeder with vanadium-alloy structure;
• helium-cooled or self/helium-cooled lithium-lead eutectic with ferritic-martensitic steel structure;
• self-cooled or helium/self-cooled molten salt blankets using ferritic-martensitic steel structures.

More advanced blankets, using for instance SiC/SiC structures, could be envisaged at a later stage if the on-going long-term R&D is successful.

The modules are mounted on equatorial port plugs and appear from outside like normal blanket modules from the shielding and thermal viewpoints. They have to be specially designed to take care of any accidents arising within the modules, and to remove tritium from the modules to avoid inventory buildup, thus testing the systems needed in a power reactor. One or more of these modules is planned to be connected to a turbogenerator, to generate electricity from fusion on earth for the first time ever.

Although the modules are mounted in a region which receives the maximum heat and neutron fluxes, the neutron fluence these modules can accumulate in ITER will not permit the necessary testing of long-term irradiation effects on materials that would allow them to be used as the basis for DEMO. This must be carried out on a separate materials test facility specialised in high fusion neutron fluxes over small regions. Nevertheless, they will be installed from the beginning of the initial H phase because valuable results on safety and TBM system operations can already be obtained then.

Due to the limited number of ports, concepts must share the same ports. Furthermore, within each concept there are several design variants to be tested. Such an arrangement requires a strong cooperation between the user group of test blanket designers, which are not members of the ITER design team but rather its customers in national laboratories. This cooperation and coordination with the ITER design is achieved through the Test Blanket Working Group, on which all interested parties are represented. This meets regularly to coordinate the design development and to develop the testing programme.