Microstructural changes occurring during the fabrication of Zr-2.5 pct Nb alloy pressure tubes by a modified route, involving hot extrusion followed by two pilgering operations with an intermediate annealing step, have been examined in detail. In the conventional fabrication route, the hot extrusion step is followed by a single cold drawing operation in which the cold work to the extent of 25 pct is imparted to the material for achieving the required mechanical properties. Tensile properties obtained at each stage of fabrication have been evaluated and compared between the two processes. The main aim of this work has been to produce a microstructure and texture which are known to yield a lower irradiation growth. Additionally, suitable annealing conditions have been optimized for the intermediate annealing which annihilates the cold work introduced by the first cold pilgering operation without disturbing the two-phase elongated microstructure. This elongated α+ β
 I
 microstructure is required for obtaining the desired level of strength at 310 °C. The final microstructure and the crystallographic texture of the finished pressure tube have been compared with those reported for the conventionally processed material.

Evolution of microstructure during fabrication of Zr-2.5 Wt pct Nb alloy pressure tubes

Stress-reorientation of hydrides and hydride embrittlement of Zr-2.5 wt% Nb pressure tube alloy

Terminal solid solubility of hydrogen in Zr-alloy pressure tube materials

Microstructural and textural developments during Zircaloy-4 fuel tube fabrication

Delayed hydride cracking in Zr–2.5Nb pressure tube material☆

Cold-worked Zr-2.5 wt% Nb pressure tubes for Canada Deuterium Uranium Pressurized Heavy Water Reactors are made by hot extruding hollow billets into tubes that are cold-worked to size and to develop their tensile strength. All manufacturing steps are closely controlled, and the tubes meet very stringent specifications. To ensure that the tubes are free of unacceptable defects, the ingots, billets, and finished tubes are ultrasonically inspected. The strength and flaw tolerance of the tubes have been measured. Tubes removed from both research and operating power reactors have been examined to measure changes in each of these properties due to the effects of reactor operaton. All tests show that cold-worked Zr-2.5 wt% Nb pressure tubes have excellent tensile strength and resistance to failure.

B. A. Cheadle

Papers

CANDU-PHW Pressure Tubes: Their Manufacture, Inspection, and Properties