  Thousands of tons of isotopic mixtures are processed annually for heavy-water
production and tritium decontamination. The existing technologies remain
extremely energy intensive and require large capital investments. New
approaches are needed to reduce the industry's footprint. Recently, micron-size
crystals of graphene were shown to act as efficient sieves for hydrogen
isotopes pumped through graphene electrochemically. Here we report a
fully-scalable approach, using graphene obtained by chemical vapor deposition,
which allows a proton-deuteron separation factor of ca. 8, despite cracks and
imperfections. The energy consumption is projected to be orders of magnitude
smaller with respect to existing technologies. A membrane based on 30 m2 of
graphene, a readily accessible amount, could provide a heavy-water output
comparable to that of modern plants. Even higher efficiency is expected for
tritium separation. With no fundamental obstacles for scaling up, the
technology's simplicity, efficiency and green credentials call for
consideration by the nuclear and related industries.
