The international campaign to install and operate six prototype breeding-blanket concepts inside ITER’s equatorial ports—the first-ever test of tritium breeding and energy extraction in a burning-plasma environment.
A commercial fusion power plant must breed its own tritium fuel by capturing the 14.1 MeV neutrons produced in D–T reactions in a lithium-bearing blanket surrounding the plasma. No experiment has yet demonstrated net tritium breeding in a fusion neutron environment, and the Test Blanket Module (TBM) programme inside ITER is designed to provide exactly that demonstration.1 Three equatorial ports on the ITER vessel—ports 2, 16, and 18—are reserved for TBM installation, each large enough to accommodate two blanket modules side by side.
Six distinct blanket designs have been developed by ITER Members, spanning two broad families: solid-breeder concepts that use lithium ceramics (Li₄SiO₄ or Li₂TiO₃) with beryllium or beryllide neutron multipliers, and liquid-breeder concepts that circulate lithium–lead eutectic (Pb-17Li) as both breeder and coolant or heat-transfer medium.
The solid-breeder entries include the European Helium-Cooled Pebble Bed (HCPB), the Japanese Water-Cooled Solid Breeder (WCSB), and the Korean Helium-Cooled Solid Breeder (HCSB). The liquid-breeder entries include the European Helium-Cooled Lithium–Lead (HCLL), the Chinese Helium-Cooled Lithium–Lead (CN-HCLL), and the Indian Lead–Lithium Ceramic Breeder (LLCB).2
Each TBM must survive surface heat fluxes up to 0.5 MW/m² and volumetric nuclear heating of several MW/m³ while extracting bred tritium at parts-per-million concentrations from either solid pebble beds or flowing liquid metal. The modules connect through long pipe runs to ancillary systems housed in the ITER port-cell area, where tritium is recovered, measured, and accounted for. Electromagnetic loads during plasma disruptions impose severe structural requirements on the TBM box and its attachment to the vacuum-vessel plug.3
TBM installation is planned for ITER’s D–T operational phase. Preliminary design reviews for most concepts were completed between 2015 and 2020, and fabrication of qualification mock-ups and sub-components is ongoing at laboratories in Europe, Japan, South Korea, China, and India.4 The data collected—tritium production rates, permeation losses, structural integrity under neutron irradiation, and thermal-hydraulic performance—will directly inform the blanket selection for DEMO-class power plants worldwide.
Because no two parties have chosen identical materials, coolants, or geometries, the TBM campaign will yield a comparative dataset without parallel in fusion technology, reducing the risk inherent in committing a multi-billion-euro DEMO programme to a single untested blanket line.