Patent Number: 053735412
Section: claims

1. Fuel rod for a water-cooled and moderated nuclear reactor, comprising fuel pellets enclosed in a cladding having: an inner layer of a zirconium-based alloy which contains by weight:  an outer layer of a zirconium-based alloy containing by weight, beside zirconium and unavoidable impurities:  the oxygen content being then comprised between 0.10% and 0.16% by weight,  1.20% to 1.70% tin  0.18% to 0.24% iron  0.07% to 0.13% chromium,  and having an outer layer of a zirconium-based alloy containing by weight, beside zirconium and unavoidable impurities:  1.20% to 1.70% of tin  0.18% to 0.24% of iron  0.07% to 0.13% of chromium,  and having an outer layer of a zirconium-based alloy containing by weight, beside zirconium and unavoidable impurities, 0.80% to 1.20% niobium and 0.10% to 0.16% oxygen.  1.20% to 1.70% tin  0.18% to 0.24% iron  0.07% to 0.13% chromium,  and having an outer layer of a zirconium-based alloy containing by weight, beside zirconium and unavoidable impurities:  (a) forming a composite billet having an inner layer of Zircaloy 4 and an external blank consisting of said zirconium-based alloy by end welding; extruding the billet at about 650.degree. C. for bonding said inner layer and said external blank and forming a duplex tube blank;  (b) transforming the duplex tube blank so obtained by a succession of thermo-mechanical cycles; and  (c) carrying out a final step of thermally stress-relieving said cladding.  1.20% to 1.70% tin  0.18% to 0.24% iron  0.07% to 0.13% chromium,  having an outer layer of a zirconium-based alloy containing by weight, besides zirconium and unavoidable impurities:  (a) providing a composite billet containing an internal layer of Zircaloy 4 and an outer blank consisting of the zirconium-niobium-oxygen alloy, by end welding;  (b) extruding said billet at about 650.degree. C.;  (c) transforming the duplex-tube blank so obtained by a succession of thermometallurgical cycles comprising intermediary recrystallization heat treatments between rolling steps; and  (d) carrying out a final recrystallization step. 2. Fuel rod for a water-cooled and moderated nuclear reactor, comprising fuel pellets enclosed in a stress-relieved cladding having an inner layer of a zirconium-based alloy which contains by weight: 3. Fuel rod for a water-cooled and moderated nuclear reactor, comprising fuel pellets enclosed in recrystallized cladding having an inner layer of a zirconium-based alloy which contains: 4. Rod according to claim 2, wherein an amount of up to 0.05% of Fe or Cr in the iron content of the outer layer is replaced with an equivalent amount of vanadium. 5. Method for manufacturing a cladding for a nuclear fuel element, said cladding having an inner layer of Zircaloy-4 which contains: 0. 35% to 0.65% tin 6. Method according to claim 5, wherein the final annealing is performed at about 485.degree. C. 7. Method according to claim 5, wherein the cycles comprise successive annealings at about 735.degree. C. and 700.degree. C. 8. Method for manufacturing a cladding of a nuclear fuel rod, said cladding having an inner layer of Zircaloy 4 which contains: 9. Method according to claim 8, wherein the final recrystallization heat treatment is carried out at about 580.degree. C. 10. Method according to claim 8, wherein the intermediary recrystallization heat treatments are carried out at about 582.degree. C. and 700.degree. C.