Oxidation of carbon deposits as a fuel removal technique for application in fusion devices

Abstract

In tokamaks, such as ITER, with low-temperature, low-Z walls (Be or C), it is predicted that codeposition of hydrogen fuel with sputtered wall atoms will be the dominating mechanism for in-vessel tritium retention. Limits on in-vessel inventory will require the periodic removal of such tritium, and a variety of procedures have been proposed. In the case of carbon-based deposits, it is possible to use chemical reactions with oxygen to produce volatile products, which may be removed from the vacuum vessel via the vacuum pumps. Thermo-oxidation has some major advantages compared to other techniques for removing tritium from codeposits, in that it can act on all surfaces inside the vessel, including tile gaps and other non-line-of-sight surfaces, and there is no requirement for mechanical entry into the torus. This paper discusses recent experimental results and the use of oxidation in future tokamaks such as ITER.