Patent Number: 052232069
Section: description

DETAILED DESCRIPTION OF THE INVENTION In accordance with this invention, the two main components of a composite constructed nuclear fuel container, comprising a tubular container component, or tube stock unit for forming same, and a barrier liner or lining stock unit for forming same, each of some what different metal compositions such as a zirconium alloy and a zirconium metal are separately heat treated at optimum conditions for producing specifically desired properties in each prior to the assembly and uniting into a single composite unit. Thus, the tubular container component, or tube stock unit therefor, is separately heat treated. For example, a unit composed of the commercially available zirconium alloy marketed as zircaloy-2 (U.S. Pat. No. 2,772,964, and No. 4,164,420) can be heated up to about 970.degree. C. uniformly throughout to convert the alpha phase microcrystalline structure of this alloy composition to a substantially alpha plus beta phase structure, and then rapidly cooled to preserve the heat induced structural phase. Additionally the barrier liner components, or lining stock unit therefor, is also separately heat treated. For example, a unit composed of a relatively pure zirconium metal (U.S. Pat. No. 4,372,817) can be heated up to about 900.degree. C. uniformly throughout to convert the alpha phase microcrystalline structure of this metal composition to a substantially beta phase structure, and then rapidly cooled to preserve the heat induced structural phase. Following their separate optimized heat treatments, the tubular container component and the barrier liner component, or the stock units therefor, are assembled together and combined by inserting the hollow barrier liner into and through the length of the tubular container. The combined units are then metallurgically bonded by conventional means, such as explosive bonding, into a single integrated composite of a lined tubular container for nuclear fuel. Typically the separately heat treated components for composite constructed nuclear fuel containers, comprise large diameter container tube stock and liner stock which are assembled into a composite are then reduced together in circumference in at least one and preferably a series of reduction steps repeated until the desired diameter is attained for a fuel container. In accordance with the practice of the art, the composite unit is annealed following each reduction to relieve stresses imposed by the compression of the reductions. Annealing temperatures should be below the previously imposed microstructure modifying heat treating temperatures to preclude reversing the modified microstructure, for example not above about 600.degree. C.