The Canada Deuterium Uranium (CANDU) pressurized heavy water (PHW) reactor is a pressure tube reactor moderated with heavy water and cooled with either light or heavy water. Materials used in the steam generators are chosen to be compatible with the CANDU system by considering the following:

  1. reliability
  2. activation of corrosion products
  3. cost
  4. manufacturing considerations
  5. operating requirements
  6. availability of materials
  7. material integrity.
  Tubing materials are chosen to provide resistance to corrosion and erosion in a controlled chemical environment on both sides of the tubes thus ensuring a low probability of leakage. Thus certain aspects of the feedwater system must be considered, such as avoiding copper alloys, ensuring integrity of the turbine condenser, and specifying feedwater chemistry. The steam generators in recently committed stations use Incoloy-800 tubing with a restrictive composition. Monel-400 and Inconel-600 have been used in earlier stations. The steam generators are fabricated entirely of carbon steel except for the tubing and tubesheet overlay. Materials are selected cooperatively by the steam generator manufacturer and Atomic Energy of Canada Limited (AECL). Material quality, especially tubing, is obtained through stringent specifications and quality control. AECL maintains a current expertise, and also maintains research into potential improvements primarily associated with testing of alternative tube alloys and water chemistry effects on these alloys.