A safe, reliable chemical reactor (1, 20) with a simple construction, easy to assemble and to disassemble comprises a casing (2), a male member (3) supported by the casing (2) and inserted with a certain clearance in a female member (4) associated to the casing (2), as well as a metallic foil (10) capable of being deformed fixedly connected to the male member (3) and protruding into said clearance (8), in order to hinder the fluid passage through the clearance.