THINNED PIPE MANAGEMENT PROGRAM OF KOREAN NUCLEAR POWER PLANTS

Abstract

Local wall thinning and integrity degradation caused by several mechanisms, such as flow accelerated corrosion(FAC), cavitation, flashing and/or liquid drop impingements, are a main concern in carbon steel pipingsystems of nuclear power plant in terms of safety and operability. Thinned pipe management program (TPMP)had been developed and optimized to reduce the possibility of unplanned shutdown and/or power reductiondue to pipe failure caused by wall thinning in the secondary side piping system. This program also consistsof several technical elements such as prediction of wear rate for each component, prioritization of componentsfor inspection, thickness measurement, calculation of actual wear and wear rate for each component. Decisionmaking is associated with replacement or continuous service for thinned pipe components. Establishmentof long-term strategy based on diagnosis of plant condition regarding overall wall thinning is also essentialpart of the program. Prediction models of wall thinning caused by FAC had been established for 24 operatingnuclear plants. Long term strategies to manage the thinned pipe component were prepared and applied toeach unit, which was reflecting plant specific design, operation, and inspection history, so that the structuralintegrity of piping system can be maintained. An alternative integrity assessment criterion and a computerprogram for thinned piping items were developed for the first time in the world, which was directly applicableto the secondary piping system of nuclear power plant. The thinned pipe management program is appliedto all domestic nuclear power plants as a standard procedure form so that it contributes to preventing anaccident caused by FAC.