FY2004 CORROSION SURVEILLANCE RESULTS FOR L-BASIN
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 2004 results are compared to previous results on coupons removed from SRS basins in fiscal years 2001, 2002 and 2003. The extent of corrosion is correlated with sample and storage conditions as well as the water chemistry during the storage period. Coupon weight gains from 2004 coupons are similar to those from 2003. Oxides were removed from furniture rack coupons from 2003 and 2004 and comparable pit depths were found in the filler metal. Corrosion induced-degradation of the spent nuclear fuels stored in L-Basin could potentially impact the storage process by causing cladding penetration, exposing fuel core material, and allowing release of radionuclides to the basin waters. Such releases could potentially lead to high water activity levels which could impact fuel integrity and present problems in future fuel handling and transfer operations. However, the collective results (to date) of the coupon and water chemistry evaluations and Uruguay spent fuel inspections indicate that the fuel in the SRS storage basins has not experienced corrosion-induced degradation that will limit the time for interim storage in the basin waters. Continued surveillance and inspection is essential due to the potential for corrosion induced degradation. The next withdrawal of surveillance coupons from L-Basin occurred on March 29, 2005.
- Research Organization:
- Savannah River Site (SRS), Aiken, SC (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- DE-AC09-96SR18500
- OSTI ID:
- 890163
- Report Number(s):
- WSRC-TR-2005-00067; TRN: US0604720
- Country of Publication:
- United States
- Language:
- English
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