Patent Number: 
Section: claims

1. A method of producing a cladding tube for nuclear fuel for a nuclear boiling water reactor, which method comprises the following steps:forming a tube comprising:an outer cylindrical component comprising a first composition comprising a zirconium-based alloy; andan inner cylindrical component metallurgically bonded to the outer component, wherein the inner component comprises a second composition comprising 0.1 to 0.4 percentage by weight Sn, 400 to 1500 ppm Fe, less than 600 ppm O and the rest Zr, except for impurities of a content that does not exceed that which is normally accepted in Zr or Zr-alloys for applications in nuclear reactors,wherein the first and second compositions materially differ from each other, and wherein the second composition has a lower recrystallization temperature than the first composition;rolling the tube; andfinally annealing the cladding tube at a temperature and a time that results in a first degree of recrystallization of the outer component and a second degree of recrystallization of the inner component, wherein the second degree is at least 97 percent and wherein the first degree is less than the second degree and higher than 50%. 2. A method according to claim 1, wherein the second degree of recrystallization is 100% and the first degree of recrystallization is between 50% and 96%. 3. A method according to claim 1, wherein the first composition comprises Zircaloy 2 or Zircaloy 4. 4. A method according to claim 1, wherein the inner component has a thickness such that it constitutes between 3% and 30% of the total thickness of the cladding tube. 5. A method according to claim 1, wherein the step of finally annealing is carried out at a temperature between 485° C. and 550° C. 6. A method according to claim 1, wherein the step of finally annealing is performed for 1 h to 6 h. 7. A cladding tube for nuclear fuel for a nuclear boiling water reactor, which cladding tube comprises:an outer cylindrical component comprising a first composition comprising a zirconium-based alloy and having a first recrystallization temperature, wherein the outer cylindrical component has a first degree of recrystallization higher than 50 percent; andan inner cylindrical component comprising a second composition comprising 0.1 to 0.4 percentage by weight Sn, 400 to 1500 ppm Fe, less than 600 ppm O and the rest Zr, except for impurities of a content that does not exceed that which is normally accepted in Zr or Zr-alloys for applications in nuclear reactors, and having a second recrystallization temperature lower than the first recrystallization temperature, wherein the inner cylindrical component has a second degree of recrystallization greater than the first degree of recrystallization and at least 97 percent, wherein the inner cylindrical component is metallurgically bonded to the outer component, and wherein the first and second compositions materially differ from each other. 8. A cladding tube according to claim 7, wherein the second degree of recrystallization is 100% and the first degree of recrystallization is between 50% and 96%. 9. A cladding tube according to claim 7, wherein the first composition comprises Zircaloy 2 or Zircaloy 4. 10. A cladding tube according to claim 7, wherein the inner component has a thickness such that it constitutes between 3% and 30% of the total thickness of the cladding tube. 11. A method according to claim 1, wherein the second degree of recrystallization is at least 97 percent and the first degree of recrystallization is between 70 percent and 90 percent. 12. A cladding tube according to claim 7, wherein the second degree of recrystallization is 100% and the first degree of recrystallization in the outer component is between 70 percent and 90 percent. 13. The method of claim 1, wherein the step of finally annealing is carried out at a temperature between 485° C. and 515° C. 14. The method of claim 1, wherein the second composition consists essentially of 0.1 to 0.4 percentage by weight Sn, 400 to 1500 ppm Fe, less than 600 ppm O and the rest Zr, except for impurities of a content that does not exceed that which is normally accepted in Zr or Zr-alloys for applications in nuclear reactors. 15. The cladding tube according to claim 7, wherein the second recrystallization temperature is between 485° C. and 550° C. 16. The cladding tube according to claim 15, wherein the second recrystallization temperature is between 485° C. and 515° C. 17. The method of claim 10, wherein the step of finally annealing is carried out at a temperature between 485° C. and 515° C. 18. The method of claim 1, wherein the first degree of recrystallization is between 60 percent and 90 percent. 19. The cladding tube of claim 7, wherein the first degree of recrystallization is between 60 percent and 90 percent. 20. A fuel assembly for a nuclear boiling water reactor, comprising:an enclosing tube; anda plurality of cladding tubes according to claim 7 filled with nuclear fuel, wherein said plurality of cladding tubes are arranged inside said enclosing tube.