Repair of nuclear steam supply system piping in pressurized water reactor power plant

Repair of Nuclear Steam Supply System (NSSS) piping in a Pressurized Water Reactor (PWR) power plant is not a frequent occurrence. However, overhaul of primary coolant pumps or replacement of steam generators may require cutting and repair of NSSS primary coolant piping. Should cutting of NSSS primary coolant piping become necessary, specific attention needs to be given to the technical details for the repair of the piping system. The primary coolant piping forms a closed loop among primary components, namely reactor vessel, primary coolant pumps and steam generators. The cutting of primary piping will induce movements in each primary component and consequentially piping nozzles at the cut as a result of stress relief. Careful monitoring of those movements and understanding of stress condition in the precut configuration are essential to he subsequent repair of the piping. Even though many nuclear plants have gone through primary coolant piping repair as a result of steam generator replacement, more nuclear plants are still planning to perform replacement. This presentation is intended to share repair experience of Combustion Engineering NSSS piping at the Palisades Plant in all phases of technical considerations so that other plants may benefit