Patent Number: 
Section: abstract

A method of fine surface finishing a cladding tube for a nuclear fuel element comprising a cladding tube containing fuel pellets, comprises heating the tube to thermal creep temperatures (e.g., 1750-2000 degrees Celsius) for sapphire and forming inner and outer surfaces of the tube to reduce ridge heights while limiting changes in the crystalline structure of the bulk of the tube. Alternatively, the tube may be placed in a mould and heating the tube-mould assembly to the range of the creep temperature of the sapphire at which differential thermal expansion of the mould and tube cause pressure at an interface between the sapphire and the mould. Maintaining the assembly at an upper end of the creep temperature range allows creep to progress and relieve stresses resulting from the pressure; and cooling the assembly to allow the sapphire tube to part from the mould and be withdrawn.