5 Design and aging management for feeder pipe and feeder supports

Feeder pipes are part of the CANDU (CANada Deuterium Uranium) reactor primary heat transport system. An essential function of the feeder pipe is to transport heavy water coolant to and from fuel channels (FCs) and to cool the fuel bundles located in the pressure tubes. Feeders and feeder supports are classified as nuclear Class 1 piping components and are designed in accordance with the requirements of the Canadian Standards Association Standard CSA N285.0, and ASME BPV Section III NB-3600 and Section III NF. The feeder pipes operate in an environment of high primary coolant pressure, temperature, and flow velocity. There are several aging mechanisms affecting the feeder pipe material, such as flow-accelerated corrosion, low temperature creep cracking, and/or stress corrosion cracking. Failure of the feeders could result in radiological consequences that exceed the health and safety limits for normal operation. An integrated aging management program (AMP) accommodating inspection, monitoring, fitness for service assessment, maintenance, and operating experience (OPEX) is required to ensure the structural integrity of feeders over the operating life of a given nuclear power plant. In order to mitigate/prevent failures resulting from degradations captured through OPEX and to extend the operating life of the feeder, design changes to the feeder and feeder supports have been applied to newly replaced feeders. This chapter summarizes practices used in the design and the AMP of feeders together with design improvements applied to newly replaced feeders through refurbishment projects conducted in Canada and South Korea.