Published: Jan 2002
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The Zircaloy-2 calandria tubes in a CANDU nuclear reactor separate the hot Zr-2.5Nb pressure tubes from the cool moderator. These tubes are about 6 m long, have an outside diameter of 132 mm, and a wall thickness of 1.4 mm. To date, their performance has been exemplary. A possible feature for future reactors is to increase the strength of these calandria tubes to reduce the economic consequences of a hypothetical accident. The current method of fabrication is to form a sheet of Zircaloy-2 into a cylinder, then weld along the length. In fixed-end burst tests such tubes always fracture in the weld area because of the differences in crystallographic texture between the parent metal and the weld; eliminating the weld would increase the strength and ductility of the tube. We have evaluated four manufacturing routes for seamless tubes. To realize high biaxial strength, we require a large fraction of basal plane normals in the radial direction, FR. This paper describes these manufacturing routes, the calandria tube properties generated by the individual manufacturing routes, and their applicability for the CANDU system. The results show that the biaxial strength of a seamless calandria tube becomes greater with an increase in FR, which is related to the amount of cold work used to make the tubes, with saturation in FR after about 95% cold work. The results are interpreted in terms of anisotropic factors determined from uniaxial tension tests.
calandria tube, Zircaloy-2, cold-work, roll-extrusion, tube reduction, crystallographic texture, biaxial strength
Senior scientist, Atomic Energy of Canada Limited, Fuel Channels Division, Chalk River Laboratories, Chalk River, Ontario
Researcher Emeritus, Atomic Energy of Canada Limited, Fuel Channels Division, Chalk River Laboratories, Chalk River, Ontario