Microstructural investigation of irradiation assisted stress corrosion cracking mechanism based on focused ion beam analysis of tested and industrial specimens.

The main objective is to study the microstructure and morphology of SCC cracks of tested and industrial specimens. The aim of this study is to provide additional experimental results that could help to rationalize existing methodologies used to analyze the failure of internals. Obtained results will be analyzed in the light of the existing threshold methodology as well as on the basis of a recently proposed quasi brittle fracture model assuming an internal oxidation SCC mechanism. In this study an analysis of O-ring samples tested in the constant load experiment will be performed by utilizing the SEM and TEM. We foresee different type of analyses to be carried out: • Analysis of non-fractured irradiated O-rings on stressed and compressed areas to see whether initiation sites are present. • Analysis of the crack statistics at the outer surfaces and fracture surfaces (branching) of fractured O-rings as function of applied stress and test time (both non-irradiated and irradiated samples). • Analysis of irradiation induced defects by TEM • An energy dispersive X-ray (EDS) spectroscopy, combined with both SEM and TEM, of the same tested O-ring specimens used in the study related to cracking statistics. • Analysis of the grain boundaries of the samples by TEM, in particular oxidized grain boundaries at the crack tip. Some of these materials were retrieved from the inside of a nuclear reactor and are considered as unique test material. Out hot cell facilities and associated experimental techniques provide unique environment and possibility to perform proposed study. In addition, recent acquisition of focused ion beam (FIB) experimental setup at SCK.CEN will allow accurate sample extraction from relevant specimen regions, e.g. close to and beyond the crack tip. Microstructural analysis at the crack tip is expected to provide crucial information in order to elucidate the complex mechanism responsible for irradiation assisted stress corrosion cracking (IASCC).

Keywords:NUCLEAR RESEARCH, MATERIAL STRUCTURE, MICROSCOPIC CHARACTERIZATION

Disciplines:Materials science and engineering, Other materials engineering, Other engineering and technology

Project type:Collaboration project