Cracking and failure of Control Rod Guide Tube (CCRGT) Support Pins (Split Pins) was encountered at a number of pressurized water reactors.
The failures in this highly stressed location have been attributed to stress corrosion cracking (SCC). Prior efforts to resolve this issue included improvements in the heat treatment and in the pin geometry. However, these changes did not significantly reduce the stress levels to prevent stress corrosion attack.
O’Donnell performed studies to establish design improvements to reduce possibilities of failures. Extensive finite element analyses were performed in which the split pin was subjected to preload, bending and thermal shock loading conditions. Since the stresses were high and the water contains sufficient oxygen to initiate the SCC mechanism, various methods were sought to generate an initial compressive stress on the surface at the neck of the split pin (most highly stressed area). The results confirmed the feasability of quenching to induce compressive stresses in this location.
– Assessment of Welding Procedures Used to Attach Appendages to P91 Heavy Wall Pipe
– Failure of Nuclear Thermal Shield Subjected to Flow Induced Vibration
– Nuclear Power Plant Consulting
– Publications – Heat Exchangers, Pressure Vessels, Welds and Other Applications, Fatigue, Elevated Temperature