A Methodology for the Management of Stress Corrosion Cracking in Ageing Pressurised Water Reactor Plants

As the operating lifetimes of nuclear plants are increasing, effective management of ageing assets is required to ensure continued safety and performance. Prolonging of plant lifetimes increases exposure to the three fundamental precursors for Stress Corrosion Cracking (SCC); tensile stress, corrosive environment and susceptible material. The majority of SCC initiation in civil nuclear plants was previously limited to occluded/stagnant dead leg regions subjected to a discrete environment, although it has been recognised instances can occur within good quality primary coolant. Recent operational experience has demonstrated the influence of historical actions and their impact on the management of ageing Pressurised Water Reactor (PWR) plants. The culmination of sensitised material, maintenance activities introducing oxygenated conditions and residual stresses has led to initiation in regions previously considered to be low risk. This paper reviews the initiating and growth conditions of SCC within ageing PWR and the methodology for the management of risk when considering plant life extensions through: a) Review of plant components against SCC initiators and contributory factors including material susceptibility to sensitisation, manufacturing processes inducing elevated stresses and entrapment of oxygenated conditions during build and through life maintenance activities. b) Quantification of the level of risk for plant components to identify regions which may have previously been considered negligible. c) Review of the availability and suitability of current In-Service Inspection techniques to inform of the level of risk. d) Considerations of plant management for the mitigation of SCC initiation and growth during periods of deviation from normal operating conditions.