AbstractThe behavior of deuterium in thermal convection loops with molten Pb17Li was investigated in the temperature range from 300 to 610°C, and in the range of deuterium partial pressures from 0.05 to 1000 mbar. Dissolution and desorption are controlled by diffusion through a 0.02 mm thick LM boundary layer at the interface, no chemical reactions are involved in the rate determining step. This boundary layer is also effective in case of permeation through membranes, if one side is covered by the LM. The permeation through 0.6 mm iron was reduced by a factor of 100. However in case of a fusion reactor blanket this boundary layer will not be important, because the wall thickness of the components is much larger. For the 2 mm stainless steel of the thermal convection loops with a downstream oxide layer, no effect of the boundary layer could be seen. The amount of oxides in the loop had no influence on the results. Furthermore an excess of H2 at low partial pressures did not change transfer rates of deuterium.The solubility of deuterium in the LM was determined from the kinetics of loading and degassing. The found values are one order of magnitude smaller than the lowest values so far published.The transport behavior of the rare gases He, Ne, Ar, Kr and Xe was investigated. The solubility of helium was found five orders of magnitude lower than that of deuterium, those for Ne, Ar, Kr and Xe even lower than that for helium. Helium-bubble formation has to be considered if the flow rate of the LM in a blanket is small, or in case of static irradiation experiments. On the other hand argon can be used as covergas for a fusion reactor blanket. Because of the low solubility in the LM, the Ar-41 activity will be much smaller than in sodium cooled reactors.