Patent Number: 056489951
Section: claims

1. A method of manufacturing a tube for constituting at least an outer part of a sheath of a nuclear fuel rod or a guide tube of a nuclear fuel assembly, comprising the steps of: (a) forming a bar of an alloy of zirconium containing 50 ppm to 250 ppm iron, 0.8% to 1.3% by weight niobium, less than 1600 ppm oxygen, less than 200 ppm carbon, and less than 120 ppm silicon;  (b) heating the bar to between 1000.degree. C. and 1200.degree. C. and quenching the bar in water;  (c) extruding a blank from said bar after heating said bar to the range 600.degree. C. to 800.degree. C.;  (d) cold rolling said blank in at least four passes to obtain a tube, with intermediate heat treatments in the range 560.degree. C. to 620.degree. C.; and  (e) performing a final heat treatment in the range 560.degree. C. to 620.degree. C., 2. A method according to claim 1, wherein step (d) includes four or five cold rolling passes starting from the extruded blank. 3. A method according to claim 1, further comprising a step of carrying out a heat treatment at a temperature in the range 560.degree. C. to 620.degree. C. after step (c). 4. A method according to claim 1, wherein said intermediate heat treatments are performed for a period of two hours to four hours, at a set temperature in the range 565.degree. C. to 605.degree. C. 5. A method according to claim 1, wherein the final heat treatment is performed for a period of two to four hours at a temperature lying in the range 565.degree. C. to 605.degree. C. 6. A method according to claim 5, wherein the final heat treatment is a temperature of about 580.degree. C. 7. A method according to claim 1, wherein the iron content is about 150 ppm. 8. A method according to claim 1, wherein the oxygen content lies in the range 1000 ppm to 1600 ppm. 9. A sheathing tube for a fuel assembly of a PWR made of a zirconium-based alloy in fully recrystallized condition, having 50 ppm to 250 ppm iron, 0.8% to 1.3% by weight niobium, 1000 ppm to 1600 ppm oxygen, less than 200 ppm carbon, less than 120 ppm silicon, the balance being zirconium and unavoidable impurities.