In graphite-moderated reactors, fissile uranium rods are placed inside graphite blocks. These blocks act as a neutron moderator whose purpose is to slow down fast-moving neutrons so that nuclear chain reactions can occur with thermal neutrons. During their use, some of the non-radioactive carbon-12 and carbon-13 isotopes in graphite get converted into radioactive C by capturing neutrons. When the graphite blocks are removed during station decommissioning, their induced radioactivity qualifies them as low-level waste requiring safe disposal.
Researchers at the University of Bristol demonstrated that a large amount of the radioactive C was concentrated on the inner walls of the graphite blocks. Due to this, they propose that much of it can be effectively removed from the blocks. This can be done by heating them to the sublimation point of  which will release the carbon in gaseous form. After this, blocks will be less radioactive and possibly easier to dispose of with most of the radioactive C having been extracted.
Those researchers propose that this C gas could be collected and used to produce man-made diamonds by a process known as chemical vapor deposition using low pressure and elevated temperature, noting that this diamond would be a thin sheet and not of the stereotypical diamond cut. The resulting diamond made of radioactive C would still produce beta radiation which researchers claim would allow it to be used as a betavoltaic source. Researchers also claim this diamond would be sandwiched between non-radioactive man-made diamonds made from C which would block radiation from the source and would also be used for energy conversion as a diamond semiconductor instead of conventional silicon semiconductors.