Advanced assessment of ductile tearing in nuclear reactor pressure vessel steel using x-ray tomography

Reactor pressure vessels (RPV) are manufactured from medium strength low allow ferritic steel specifically selected of its high toughness and weldability. The ability of the RPV to withstand crack propagation is crucial to maintaining the operational safety of the reactor plant. Current generations of RPV steels operate at sufficiently high temperatures to ensure that the material remains ductile during its service life. Furthermore, new materials are engineered to exhibit greater ductility and fracture toughness throughout their operating life. Therefore understanding and being able to predict the ductile fracture behaviour is critical for assuring the safety of RPV steels during operating conditions. This paper presents the results of an experimental programme aimed at using 3D X-ray tomography to quantify the volume fraction of ductile voids in tested pre-cracked specimens manufactured from A508 Class 3 RPV steel. The results indicate a high concentration of voids very close to the fracture surface and voids extending 3.6mm below the crack. The data and experimental methodology could be used to calibrate predictive mechanistically based models such as the Gurson-Tvergaard-Needlman (GTN).