Patent Number: 
Section: claims

1. A method of producing a coating resistant to hydration on at least one surface of a cladding tube for nuclear fuel for use for use in a light water reactor, the cladding tube comprising a liner layer on an inside of the tube, the liner layer comprising zirconium or a zirconium alloy, the method comprising: forming a coating at least on a surface of the liner layer that faces an inner space of the cladding tube by subjecting the cladding tube to a treatment with a gas mixture while heating the cladding tube, the treatment being performed at a temperature of about 450xc2x0 C. to about 650xc2x0 C. and substantially at atmospheric pressure, the gas mixture comprising water steam and both oxygen gas and nitrogen gas, wherein the coating is formed such that it has a thickness of at least one xcexcm, such that the coating at least forms an innermost surface facing the inner space of the cladding tube. 2. The method according to  claim 1 , wherein the coating is produced by making at least one of the oxygen gas and nitrogen gas of the gas mixture react with at least one material located in the surface of the liner layer. claim 1 3. The method according to  claim 1 , wherein the coating comprises by at least one of an oxide and a nitride of zirconium. claim 1 4. The method according to  claim 1 , wherein the treatment is controlled by adding at least one gas that is inert at the temperature and pressure of the treatment. claim 1 5. The method according to  claim 4 , wherein the inert gases comprise at least one of argon, helium and neon. claim 4 6. The method according to  claim 1 , wherein the treatment is controlled by varying the amount of water steam in the gas mixture. claim 1 7. The method according to  claim 1 , wherein the coating formed on the surface or the surfaces of the cladding tube during the treatment comprises at least one of zirconium dioxide and zircondium nitride. claim 1 8. The method according to  claim 1 , wherein the cladding tube is annealed a plurality of times prior to the treatment in order to confer mechanical strength, and that the treatment represents a final annealing performed in the same plant as the plurality of annealings. claim 1 9. A method according to  claim 1 , characterized in that the gas mixture contains air. claim 1 10. A method according to  claim 1 , characterized in that the gas mixture comprises further carbon dioxide (CO 2 ). claim 1 11. A method according to  claim 1 , characterized in that the gas mixture comprises further mixtures of carbon monoxide (CO) and carbon dioxide (CO 2 ). claim 1 12. A method according to  claim 1 , characterized in that the gas mixture comprises further dinitrogen oxide (N 2 O). claim 1 13. The method according to  claim 1 , wherein the treatment is performed for a period of 1 to 10 hours. claim 1