Leak tightness tests on actively cooled plasma facing components: Lessons learned from Tore Supra experience and perspectives for the new fusion machines

•Test procedures for the qualification of the tightness of actively cooled plasma facing components were defined.•The test is performed after the component manufacturing and before its set-up in the vacuum vessel.•It allows improving the fusion machine availability.•The lessons of tests over 20 years at Tore Supra are presented. The fusion machines under development or construction (ITER, W7X) use several hundreds of actively cooled plasma facing components (ACPFC). They are submitted to leak tightness requirements in order to get an appropriate vacuum level in the vessel to create the plasma. During the ACPFC manufacturing and before their installation in the machine, their leak tightness performance must be measured to check that they fulfill the vacuum requirements. A relevant procedure is needed which allows to segregate potential defects. It must also be optimized in terms of test duration and costs. Tore Supra, as an actively cooled Tokamak, experienced several leaks on ACPFCs during the commissioning and during the operation of the machine. A test procedure was then defined and several test facilities were set-up. Since 1990 the tightness of all the new ACPFCs is systematically tested before their installation in Tore Supra. During the qualification test, the component is set up in a vacuum test tank, and its cooling circuits are pressurized with helium. It is submitted to 3 temperature cycles from room temperature up to the baking temperature level in Tore Supra (200°C) and two pressurization tests are performed (6MPa at room temperature and 4MPa at 200°C) at each stage. At the end of the last cycle when the ACPFC is at room temperature and pressurized with helium at 6MPa, the measured leak rate must be lower than 5×10−11Pam3s−1, the pressure in the test tank being