Patent Number: 040452883
Section: claims

1. A nuclear fuel element comprising (a) a central core of a body of nuclear fuel material selected from the group consisting of compounds of uraniun, plutonium, thorium and mixtures thereof and (b) an elongated composite cladding container including an outer portion formed of a material selected from the group of zirconium and zirconium alloys and forming a substrate, an undeformed metal barrier of constant thickness formed of a material selected from the group of niobium, aluminum, copper, nickel, stainless steel and iron metallurgically bonded on the inside surface of the substrate, said metal barrier comprising from about 1 to about 4 percent of the thickness of the cladding container and an undeformed inner layer of constant thickness formed of zirconium metallurgically bonded on the inside surface of the metal barrier, said inner layer comprising from about 5 to about 15 percent of the thickness of the cladding container, said cladding container enclosing said core so as to leave a gap between said core and said cladding during use in a nuclear reactor. 2. The nuclear fuel element of claim 1 which has in addition a cavity inside the fuel element and a nuclear fuel material retaining means comprising a helical member positioned in the cavity. 3. A nuclear fuel element of claim 1 in which the metal barrier is aluminum. 4. A nuclear fuel element of claim 1 in which the metal barrier is copper. 5. A nuclear fuel element of claim 1 in which the metal barrier is niobium. 6. A nuclear fuel element of claim 1 in which the metal barrier is nickel. 7. A nuclear fuel element of claim 1 in which the metal barrier is stainless steel. 8. A nuclear fuel element of claim 1 in which the metal barrier is iron. 9. A nuclear fuel element of claim 1 in which the nuclear fuel material is selected from the group consisting of uranium compounds, plutonium compounds and mixtures thereof. 10. A nuclear fuel element of claim 1 in which the nuclear fuel material is comprised of uranium dioxide. 11. A nuclear fuel element of claim 1 in which the nuclear fuel material is a mixture comprising uranium dioxide and plutonium dioxide. 12. A composite cladding container for nuclear reactors comprising an outer portion forming a substrate and formed of a zirconium alloy, an undeformed metal barrier of constant thickness formed of a material selected from the group of niobium, aluminum, copper, nickel, stainless steel and iron mettallurgically bonded on the inside surface of the substrate, said metal barrier comprising from about 1 to about 4 percent of the thickness of the cladding container and an undeformed inner layer of constant thickness formed of zirconium metallurgically bonded on the inside surface of the metal barrier, said inner layer comprising from about 5 to 15 percent of the thickness of the cladding container metallurgically bonded on the inside surface of the metal barrier. 13. A composite cladding container according to claim 12 in which the metal barrier is aluminum. 14. A composite cladding container according to claim 12 in which the metal barrier is niobium. 15. A composite cladding container according to claim 12 in which the metal barrier is copper. 16. A composite cladding container according to claim 12 in which the metal barrier is nickel. 17. A composite cladding container according to claim 12 in which the metal barrier is stainless steel. 18. A composite cladding container according to claim 12 in which the metal barrier is iron. 19. A nuclear fuel element which comprises an elongated composite cladding container including an outer portion formed of a material selected from the group of zirconium and zirconium alloys forming a substrate, an undeformed metal barrier of constant thickness formed of a material selected from the group of niobium, aluminum, copper, nickel, stainless steel and iron metallurgically bonded on the inside surface of the substrate, said metal barrier comprising from about 1 to about 4 percent of the thickness of the cladding container, and an undeformed inner layer of constant thickness formed of zirconium metallurgically bonded on the inside surface of the metal barrier, said inner layer comprising from about 5 to about 15 percent of the thickness of the cladding container, a central core of a body of nuclear fuel material selected from the group consisting of compounds of uranium, plutonium, thorium and mixtures thereof disposed in and partially filling said container and forming an internal cavity in the container, an enclosure integrally secured and sealed at each end of said container, and a nuclear fuel material retaining means positioned in the cavity, said cladding container enclosing said core so as to leave a gap between said core and said cladding during use in a nuclear reactor.