Leak detection design for ITER GIS gas fueling manifold

•Pressure cascade between the fueling pipes, interspace and environment, as well as interspace venting are designed for GIS safety concern.•Pressure comparation of the gas supply pipes and the interspace will indicate a relative large leak.•The hydrogen isotope and tritium concentration in the interspace venting flow will indicate a leak of dedicated gas supply pipe.•Leak-out of hydrogen is caused by diffusion and will not reach the explosion level.