Design of a radiative semi-transparent liner for the ITER divertor cassette

The increased safety concern, resulting from the accumulation of tritium in the redeposited carbon-dominated films forming on the surfaces of the ITER divertor private region plasma facing components, has stimulated an import ant change of the gas box liner design. A significant modification of the I TER divertor cassette design was undertaken in the summer of 1997 with the removal of the so-called 'wings'. This highlighted the necessity to protect the cold (150 degreesC) pumping duct from radiated heat and particle flux from the plasma chamber. A cold duct has the potential to trap unacceptably high levels of tritium in the redeposited carbon films produced from erosi on of the vertical target. To provide protection that minimises the uptake of tritium, a new semi-transparent liner operating with hot tungsten (W) ti les was proposed by the ITER Joint Central Team (JCT) and was developed by the RF Home Team. This liner design promises to minimise the amount of trit ium trapped in it by operating with the surface temperature of the W in the range 800-1200 degreesC. Radiatively cooled tiles on the surface of the li ner maintain the surface temperature between these limits, for a surface he at flux of between 0.1 and 0.35 MW/m(2), a range which takes into account t he uncertainties in the predicted operational heat loads. This paper report s on the predicted operational regime of the liner which allows effective t ransformation of incoming atomic tritium and carbon into stable hydrocarbon s, that can be pumped safely to the reprocessing plant. The role of hydroca rbons las molecules and radicals) is assessed. A sensible parametric analys is of tritium retention, on the liner surface and on cold areas behind the liner, was performed for different conditions and operational parameters. ( C) 2000 Elsevier Science B.V. All rights reserved.