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.