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Corrosion of Copper in Anoxic Groundwater Inoculated with Sulfate Reducing Bacteria and Methanogens

In Finland, nuclear waste will be disposed in a geological repository in copper canisters. Here, biotic and abiotic mesocosms, containing copper coupons and an artificial groundwater at 10 °C under argon atmosphere. Sulfate reducing bacteria and methanogens were added to the biotic experiments.

 

Product Number: 51317--9355-SG
ISBN: 9355 2017 CP
Author: Leena Carpen
Publication Date: 2017
Industry: Energy Generation
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In Finland the high level nuclear waste will be disposed in copper canisters to a geological repository at the depth of approximately 400 m below the sea level. The solid rods of spent fuel are first stored in cast iron containers which are then placed inside copper canisters with 50 mm wall thickness. The canisters are enclosed by a bentonite clay buffer. The surrounding rock will provide the last barrier in this Finnish multi-barrier concept. Copper has been chosen for the canister material due to its good corrosion resistance in anoxic water. However the colonization and activity of microbes on the surface or in the vicinity of the copper canister may initiate and accelerate several corrosion mechanisms. Bentonite buffer is supposed to inhibit the migration of bacteria into the vicinity of the canister. Nevertheless in the case of uneven saturation and swelling of the bentonite or due to formation of water-bearing fractures the groundwater and micro-organisms may come into contact with the canister.In this study biotic and abiotic (sterilized) mesocosms were assembled with copper specimens and a synthetic groundwater. Inoculation of sulfate reducing bacteria (SRB) and methanogens enriched from the disposal site was added to the biotic experiments. To simulate the later stage of the disposal when the temperature has decreased to the level of the surrounding bedrock and all the oxygen has been consumed the mesocosms were incubated at 10 °C under argon atmosphere. The chemistry of the used synthetic water was calculated to simulate the ground water of disposal site taken into account also the effects of bentonite. During the 1 year exposure several electrochemical methods such as open circuit potential linear polarization resistance and impedance spectroscopy were performed intermittently.Preliminary results from the laboratory exposure are presented and discussed in this paper. The results can be used when evaluating risks of the microbially induced corrosion of copper canister in the geological repository environment.

Key words: Microbially induced corrosion, Copper canister, High level waste, Repository conditions

In Finland the high level nuclear waste will be disposed in copper canisters to a geological repository at the depth of approximately 400 m below the sea level. The solid rods of spent fuel are first stored in cast iron containers which are then placed inside copper canisters with 50 mm wall thickness. The canisters are enclosed by a bentonite clay buffer. The surrounding rock will provide the last barrier in this Finnish multi-barrier concept. Copper has been chosen for the canister material due to its good corrosion resistance in anoxic water. However the colonization and activity of microbes on the surface or in the vicinity of the copper canister may initiate and accelerate several corrosion mechanisms. Bentonite buffer is supposed to inhibit the migration of bacteria into the vicinity of the canister. Nevertheless in the case of uneven saturation and swelling of the bentonite or due to formation of water-bearing fractures the groundwater and micro-organisms may come into contact with the canister.In this study biotic and abiotic (sterilized) mesocosms were assembled with copper specimens and a synthetic groundwater. Inoculation of sulfate reducing bacteria (SRB) and methanogens enriched from the disposal site was added to the biotic experiments. To simulate the later stage of the disposal when the temperature has decreased to the level of the surrounding bedrock and all the oxygen has been consumed the mesocosms were incubated at 10 °C under argon atmosphere. The chemistry of the used synthetic water was calculated to simulate the ground water of disposal site taken into account also the effects of bentonite. During the 1 year exposure several electrochemical methods such as open circuit potential linear polarization resistance and impedance spectroscopy were performed intermittently.Preliminary results from the laboratory exposure are presented and discussed in this paper. The results can be used when evaluating risks of the microbially induced corrosion of copper canister in the geological repository environment.

Key words: Microbially induced corrosion, Copper canister, High level waste, Repository conditions

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