Release of hydrogen isotopes from first-wall surfaces on exposure to air

This paper demonstrates that about 1.6x1023 atoms of deuterium are released on exposure of the in-vessel surfaces to air, and thus that a large part of the 'surface-reservoir' is readily accessible to the gas phase. There are two obvious corollaries of the results: firstly, samples removed from a torus for post-mortem analysis (which have inevitably been exposed to air) have already lost this component of the deuterium, and secondly, precautions must be taken before venting the vessel once significant amounts of tritium are present on the walls. We also demonstrate that glow discharge carbonisation (together with a rise in vessel temperature) prior to opening reduces the amount of deuterium and tritium released by a considerable factor. (orig./MM)