Containment penetrations - flexible metallic bellows: testing, safety, life extension issues

Although the overall performance of flexible metallic bellows penetrations has appeared to be acceptable for approximately 20 years, aging and degradation of these components has been recently identified. Corrosion and fatigue mechanisms have lead to cracking and subsequent leakage through the stainless steel bellows elements. Although periodic testing in accordance with 10CFR50, Appendix J has been performed, fabrication features of some expansion joint assemblies has accordance with 10CFR50, Appendix J has been performed, fabrication features of some expansion joint assemblies has made it difficult to collect reliable leakage rate data. In fact, recent observations suggest that it is not possible to perform valid Local Leak Rate Testing (LLRT) of certain two-ply bellows elements. The paper presents a description of efforts made to characterize the nature and significance of the bellows degradation observed. Field pressure testing and laboratory examinations are discussed, as well as evaluations to determine leak areas and leakage rates. Crack growth from both corrosion and fatigue mechanisms are examined, and methods for predicting remaining useful life are discussed. Repair and replacement methods will be summarized as well as testing to demonstrate replacement effectiveness. (orig./HP)