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PublisherNACE InternationalLanguageEnglish
Document ID 02070547
Content TypeJournal Paper
TitleAnaerobic Corrosion of Carbon Steel and Cast Iron in Artificial Groundwaters: Part 1Electrochemical Aspects
AuthorsN.R. Smart, D.J. Blackwood, and L. Werme
JournalCorrosion
VolumeVolume 58, Number 07
DateJuly, 2002
Copyright2002. NACE International.
Keywordsanaerobic corrosion, electrochemistry, hydrogen,radioactive waste, steel
PreviewABSTRACT
Sweden has 11 nuclear reactors in operation at four different sites. These reactors produce ~50% of all the electricity used in Sweden. By 2010, the current nuclear program will have produced ~8,000 metric tons of spent nuclear fuel. After spending 30 to 40 years in the central intermediate storage facility, the fuel will be encapsulated in corrosion-resistant disposal containers. Then, it will be transported to a geological repository, where the containers will be deposited at a depth of 500 m to 700 m in granitic rock and surrounded by a bentonite clay backfill material. Over a period of more than 15 years, an extensive database on groundwater chemistry has been built up. Despite the fact that the data represent widely spread geographic regions of Sweden, they present a relatively consistent picture. Groundwater in granitic rock in Sweden is oxygen-free and reducing below a depth of 100 m to 200 m. The redox potential below this depth ranges between ­200 mV and ­300 mV on the hydrogen scale, and the water pH ranges from neutral to mildly alkaline.1-2 Resistance to corrosion can be achieved in several ways. Svensk Kärnsbränslehantering AB (SKB) has decided to approach the long-term corrosion problem by choosing a container material that is as close as possible to being immune to corrosion under the expected repository conditions. Copper has a wide stability range in oxygen-free water,3 and oxygen-free conditions are expected during most of the repository performance lifetime. Dissolved sulfides in the groundwater change the situation, and copper can then corrode by formation of copper sulfides and hydrogen. The concentrations of dissolved sulfide in the near field of the canister are, however, very low, and the corrosion attack on copper, during long periods of time, will be controlled by the availability of dissolved sulfides. Pure copper has insufficient mechanical strength to withstand the external overpressure of ~14 MPa at the disposal level in the repository. This pressure is composed of a water pressure of 7 MPa, corresponding to a depth of 700 m, and 7 MPa swelling pressure
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