Corrosion issues in pressurized heavy water reactor (PHWR/CANDU®) systems

Abstract: Although the CANDU pressurized heavy water reactor (PHWR) design differs from that of light water reactors (LWRs), many of the materials degradation issues are similar. Materials common to both designs are carbon steels, low alloy steels, stainless steels and zirconium alloys. However, these materials are used for systems and components that may be quite different between these two designs. The major difference is the use of fuel channels to contain the fuel in a CANDU. These zirconium alloy fuel channels are assembled into a stainless steel ‘calandria’ vessel, which holds the heavy water moderator. Corrosion issues associated with these fuel channels are discussed in further detail in this chapter. Steam generator, heat transport and balance of plant piping and components in CANDUs are similar in materials and function to those in LWRs, but some unique aspects of operating these systems in CANDU reactors will be discussed. Finally, monitoring advances are outlined, along with a discussion of future trends in ‘smart’ technologies for improved CANDU design and operation.