AbstractA convertible blanket concept is proposed for ITER, where, without replacement of the blanket structure, a non-breeding Pb alloy is used during the basic performance phase and the eutectic Pb-17Li during the enhanced performance phase. The concept is based on austenitic steel as structural material, an average neutron wall load of 1 MW m−2 and either helium or water as coolant. The same design concept was used for both coolant options with respect to a stiff blanket segment box, direct cooling of the first wall using toroidal ducts, poloidal hairpin tubes to cool the quasi-stagnant liquid metal and tritium removal outside the vacuum vessel.Various design options were considered for the first-wall and pool cooling and corresponding headers. Owing to the different coolant properties, different combinations were selected for the two versions. The performance of the two versions was assessed among other things with respect to tritium breeding and control, reliability and R&D needs.