[en] In the operation of nuclear reactors employing sintered fuel tablets sheathed in zirconium alloy sheaths it has been found that, during irradiation, cadmium is released from the fuel and migrates outwardly to the inner surface of the sheath, where it can create an embrittlement phenomenon, resulting in sheath failure due to stress corrosion cracking. In accordance with the present disclosure copper is provided as a barrier or partial barrier between the fuel and the sheath inner surface, to facilitate the formation of a stable copper-cadmium alloy during the irradiation life of the fuel, to thereby impede the formation of a concentration of cadmium or active compounds thereof on the sheath inner surface. (auth)