1.  Field of the Invention
The present invention relates to a method for making Zr alloy cladding for nuclear reactor fuel.  The Zr alloy cladding has excellent corrosion resistance when it is exposed to hot high-pressure water or steam, and has excellent creep properties. 
2.  Description of the Related Art
A general type of nuclear reactor is a pressurized water reactor (PWR).  A cladding tube for reactor fuel used in this type of reactor is made of a Zr alloy.  A typical Zr alloy used in such a cladding tube is Zircaloy-4, which is composed of (hereinafter percentages are percent by weight) 1.2 to 1.7% Sn, 0.18 to 0.24% Fe, and 0.07 to 0.13% Cr, with the balance being Zr and incidental impurities. 
Nb- or Nb/Ta-containing Zr alloys having excellent corrosion resistance have also been proposed for cladding tubes.  The Nb-containing Zr alloy is composed of 0.2 to 1.7% Sn, 0.18 to 0.6% Fe, 0.07 to 0.4% Cr, and 0.05 to 1.0% Nb, with the balance being Zr and incidental impurities, wherein the nitrogen content as an incidental impurity is 60 ppm or less.  The Nb/Ta-containing Zr alloy is composed of 0.2 to 1.7% Sn, 0.18 to 0.6% Fe, 0.07 to 0.4% Cr, 0.05 to 1.0% Nb and 0.01 to 0.1% Ta, with the balance being Zr and incidental impurities, wherein the nitrogen content as an incidental impurity is 60 ppm or less. 
The profitability of a nuclear power plant can be increased by reacting fuel for longer periods of time.  This requires increasing the residence time of fuel cladding tubes in reactors.  However, the above-mentioned cladding tubes made of Nb-containing or Nb/Ta-containing Zr alloys do not have sufficient durability to meet long reactor residence time requirements because these alloys do not have sufficiently high corrosion resistance and sufficiently low creep properties.  Thus, there is a need for high durability nuclear fuel cladding.