Abstract: A pressure vessel for fluids containing hydrogen and subjected to a neutron flux. The vessel comprises an inner sealing layer and an outer load bearing layer. The inner sealing layer is composed of a material having a radiation induced diametral deformation rate higher than that of the outer layer to minimize stresses therein. The outer layer is provided with apertures, and the boundary between the inner and outer layers is non-metallurgical such that any fluid which penetrates the sealing layer will readily pass through the outer layer where it can be detected, by suitable detector before it produces embrittlement of the load bearing layer. The preferred application for the invention is in pressure tubes for a nuclear reactor.