Fabrication of Zirconium Alloys into Components for Nuclear Reactors

Over 80 percent of the world's annual output of zirconium is fabricated into components for nuclear reactors. In 1976 the CANadian Deuterium Uranium (CANDU) power reactor program will require nearly 500 Mg of zirconium and by 1986 the requirement will have risen to nearly 800 Mg. Most of this is fabricated into tubes which can cost as much as $80/kg. Small thin walled tubes for fuel cladding are fabricated by heavily cold working extruded tubes. The most important fabrication parameter in producing the desired crystallographic texture, hydride orientation, and mechanical properties is the cold reduction route. The deformation also must be controlled carefully to ensure that these properties are uniform, both through the wall thickness and around the circumference of the tube. Large-diameter thin-walled tubes are used to guide coolant flow, guide control rods, or for calandria tubes. These tubes can be made by seam welding annealed sheet and they can be made to very close dimensional tolerances. The weld and heat-affected zones must be recrystallized by cold work and heat treatment so that they have adequate ductility after irradiation. Pressure containment tubes usually are fabricated by hot extrusion and cold worked a limited amount to size. The most important fabrication parameters are the forging and extrusion processes because they determine the crystallographic texture and the microstructure of the tubes. The advantages of different fabrication techniques and the properties of the tubes are discussed.