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Description: This report documents the results of the L-Basin Corrosion Surveillance Program for the fiscal year 2004. Test coupons were removed from the basin on February 12, 2004, shipped to Savannah River National Laboratory (SRNL), and visually examined in a contaminated laboratory hood. Selected coupons were metallurgically characterized to establish the extent of general corrosion and pitting. Pitting was observed on galvanically coupled and on intentionally creviced coupons, thus demonstrating that localized concentration cells were formed during the exposure period. In these cases, the susceptibility to pitting was not attributed to aggressive basin water chemistry but to localized conditions (intentional crevices and galvanic coupling) that allowed the development of oxygen and/or metal ion concentration cells that produced locally aggressive waters. General oxidation was also observed on all of the coupons with localized corrosion observed on some of the coupons. These coupons were not pretreated to produce a protective oxide layer prior to exposure in the basin water. Non-protected coupons are more susceptible to corrosion than fuel cladding which has developed a protective oxide layer from high temperature reactor operations. However, the oxide on spent nuclear fuel (SNF) stored in L-Basin is not necessarily in pristine condition. Some of the oxide may have spalled off or been mechanically damaged prior to arrival at SRS. These areas on the fuel cladding would have the same susceptibility to corrosion as the coupons. Current observations from the test coupons demonstrate that, even with rigorously controlled basin water chemistry, localized aggressive conditions can develop in intentional crevice and galvanic samples. These results do illustrate the potential for corrosion induced degradation and thus the importance of a routine surveillance program similar to that conducted on the Uruguay fuel and on the surveillance coupons stored in L-Basin and future in-service inspections proposed for additional SNF in L-Basin. The ...
Date: September 5, 2005