Influence of dissolved hydrogen on PWSCC of Alloy 182 in primary water

Stress corrosion cracking is one of most severe damage mechanisms influencing the lifetime of components in the operation of nuclear power plants. When a pressurized water reactor (PWR) has been running over a long period, SCC might occur in components and structure due to the effect of the pressurized high temperature water environment. Consequently fundamental understanding of the mechanism and countermeasures against SCC are the important issues with regard to the long-term operation of the PWR. In recent years, it has also become apparent that the level of hydrogen added to prevent radiolysis have some influence in both the initiation and propagation of cracks. Changes in the hydrogen contents can do that the corrosion potential reaches the Ni/NiO boundary phase, and have some influence in the stress corrosion cracking behavior. Stress corrosion cracking mitigation by the variation of the dissolved hydrogen contents in the water in light water pressurized reactors was applied though not yet completely understood. In this work the influence of dissolved hydrogen in two different concentrations (25 and 50 cm3/kg) on nickel alloy 182 PWSCC susceptibility has been studied. For this purpose, stress corrosion test (SSRT) and electrochemical measurements were carried out. The techniques used in the characterization of the fracture surface are scanning electron microscope (SEM) combined with energy-dispersive spectrometer (EDS) to evaluate fracture morphology and chemical composition. (authors)