Managing the ageing degradation of concealed safety relevant cooling water piping in european S/KWU LWRS

Abstract

Safety relevant cooling water piping is designed to transport excess heat both from the reactor core and the fuel pool under all operational and emergency conditions. Plain carbon steels are used, with or without different types of protective coating systems. Outside of the reactor building, such piping is often buried or concealed, which also gives additional protection against damage. Relevant ageing mechanisms are shallow pit corrosion and microbiological induced corrosion (MIC). While these ageing mechanisms can lead to localized leaks and limited loss of cooling water, neither the mechanical integrity nor the cooling ability of the systems are compromised. The extent and ageing management of the mechanisms are described, based on more than 30 years of operating experience. This includes NDT results and post service examinations after retrofits. Based on this positive operational experience, two different NDT concepts are recommended to manage the long time operational ageing.