Steam generator of Vandellos nuclear power station: Operational experience

The Central Nuclear de Vandellos power station at Hospitalet del Infante, Spain, is a 500 MWe gas graphite moderated natural uranium reactor. The plant has generated over 46,000 million KWh over the past thirteen years of service. Throughout this service, the plant has suffered from THO phase erosion-corrosion damage in the steam generator sections of the system. The Vandellos steam generators are once-through units constructed of 1386 mild steel tubing (panels) each fabricated into a serpentine containing 83 horizontal passes. Four independent steam generator circuits are combined to feed two, 250 MWe turbines. Erosion-corrosion damage has caused panel element leakage in the evaporation of some tubing elements. The rate of erosion-corrosion damage has been modified through different operational changes since damage was first detected in 1975. This paper describes the different operating behavior of the four steam generators and an evaluation of damage through the expertise of different technical resource groups. The changes in plant operating technique discussed include hydrodynamic conditions and chemical treatment parameters. One of the most important changes in plant operation has been in the use of amines as alkaline agents. Solutions of ammonia were initially used for pH control of feedwater. In an effort to reduce erosion-corrosion levels below rates experienced using ammonia, a change was made to the use of morpholine, and more recently, a change to the use of AMP(2 amino-2-methyl-1-propanol) has shown favorable results. The paper outlines the overall behavior of steam generator function under plant transition conditions, and contrasts that behavior with current chemical parameters experienced using AMP treatment. Water chemistry characteristics are used to present an evaluation of the development of erosion-corrosion damages from 1976 through present operating conditions. (author)