A probabilistic fracture mechanics model for the tubing degradation of the Koeberg steam generators

Master Thesis


Permanent link to this Item
Journal Title
Link to Journal
Journal ISSN
Volume Title

University of Cape Town

The susceptibility of Steam Generator (SG) Tubes (particularly tubes manufactured from Inconel 600) to primary water stress corrosion cracking (PWSCC) has been a major concern to the nuclear industry since 1971, when this phenomenon was first observed outside the laboratory. Since the susceptibility of Inconel 600 to PWSCC in pure water was first established as a certainty, various electricity utilities have devoted considerable resources to determining the exact nature of this degradation phenomenon and to predicting its consequences. Whereas, the study of the nature of this degradation mechanism has led to many conflicting conclusions, the predictive methods developed have been more successful. Initially, the establishment of the Leak Before Risk of Break principle has allowed various utilities to justify SG operation with cracked tubes. Later, the development of probabilistic simulation methods, most notably by EdF and the Jozef Stefan Institute (JSI), have led to further justification of the existing maintenance regimes and also allowed the ability to do sensitivity studies with regards to various influencing parameters. The current maintenance regime at the Koeberg Nuclear Power Station (near Cape Town, South Africa) utilises tube plugging (when cracks exceed a certain length limit) and online leak detection (based on detection of radioactive Nitrogen 16) as the main means of ensuring safe SG operation. However, the plugging limit used is based on a conservative deterministic analysis, which may be penalising in some situations. Thus, the need for risk-based SG life-time optimisation was evident.

Includes bibliographical references (leaves 115-124).