AbstractDesign studies and R&D activities on the separate first wall for tokamak fusion experimental reactors have been progressed at JAERI. The first wall has a high probability of unexpected damage because of the uncertainties in local heat and particle loads and it requires easy replacement in case of failure. In order to satisfy the requirement of assembly and maintenance, the first wall mechanically separated and separately cooled from a massive blanket module has been proposed as a promising concept with a number of advantageous features, such as easy handling during assembly/disassembly due to light weight ( ∼350 kg), short down-time for maintenance operation, minimized amount of radwaste and so on. A fail-safe structure, which is consistent with in-service-inspection requirements, has been realized by employing a reliable double-walled thin shell structure sandwiching metal mesh. A quilting structure of austenitic stainless steel (SS316) cooled by low pressure (2 MPa), low temperature (100–150°C) water is employed to accommodate high surface heat flux of more than 0.3 MW m−2 and nuclear heating together with large electromagnetic loads up to 2 MPa. This paper describes the outlines of the structural design of the separated first wall, cooling and manifolds, mechanical connection to blanket structure, fabrication procedure, results of thermo-mechanical analyses and related R&D activities performed at JAERI.