Thermal release rate of tritium trapped in bulk and plasma exposed surfaces of carbon specimens obtained from JET divertor

Tritium co-deposition with carbon in the colder remote areas of the JET vessel immobilises a substantial amount of the fuel and increases the tritium inventory of the machine. A well defined physical or chemical description of these co-deposits is still not available. Therefore they are reported in the literature as a carbonaceous amorphous C:H layer, and unfortunately sometimes as a ‘diamond-like film’ referring to their sp3 hybridisation. From the present study it appears that the gas–solid reactions taking place during the thermal treatment of carbon samples involves various tritiated hydrocarbon species having one or two carbon atoms in their structure like methyl (CH3) or ethyl (CH2CH3), having practically all bonds saturated with heavier hydrogen isotopes. The thermal response of the samples was also investigated by laser irradiation. During the laser scans the co-deposited layers reach high temperatures, sometimes exceeding 2300 °C, releasing all co-deposited tritium to the gas phase.