Phenomena of material degradation with time relevant to reactor pressure vessels

The knowledge regarding specific technical and regulatory issues which arise in assessing long-term integrity and lifetime management of reactor pressure vessels are reviewed. The major failure risk of the reactor pressure vessel arises from material degradation due to fast neutron irradiation during the service of the plant. Better understanding of the irradiation damage of reactor pressure vessel materials is important in improving and validating the engineering methodologies for the assessment of the reactor pressure vessel integrity and safe service life. The fracture mechanics issues and their impact on the reactor pressure vessel pressurized thermal shock analysis are also discussed, including the effects of cladding on the reactor pressure vessel fracture. Since failure of the reactor pressure vessel might initiate from crack-like defects at critical locations in the vessel wall, the purpose of this presentation is also to review the design, inspection and monitoring practices as well as the occurrence of stress corrosion cracking/fatigue cracks in operating nuclear pressure vessels. Recommendations will also be provided to address the material degradation related concerns in operating nuclear power plants.