Consequences of the technology survey and gap analysis on the EU DEMO R&D programme in tritium, matter injection and vacuum

•The inner fuel cycle architecture of DEMO is developed in a systems engineering approach as a functional break-down diagram, driven by the need for inventory minimisation.•Technologies to fulfil the required functions are discussed and ranked.•Prime technologies are identified and an associated R&D programme is developed.•The core challenges of a DEMO fuel cycle beyond those already addressed in ITER are discussed.