Abstract: A spallation target and a proton accelerator were needed for an accelerator driven sub-critical system (ADS) to provide continual neutron sources for the blanket. For the windowed target, light nuclides easily permeate the interface of the proton tube and target. The influence of light spallation productions on the vacuum of the proton tube was analysed. First software was used to simulate the spallation production yields, then, in combined the permeation and flow conductance calculation, pressure in the proton tube was obtained. At last, parameters of PDS-XADS were partly used to give a numerical result to get a visual impression.

Key words: ADS, proton tube, hydrogen permeation