ABSTRACT
In Finland, the high level nuclear waste will be disposed in a geological repository, at the depth of 400- 450 m below the sea level. The solid spent fuel rods are placed in cast iron containers, covered with 50 mm thick copper sheet, which are enclosed by a bentonite clay buffer. The surrounding rock provides the final barrier in this multi-barrier concept. Copper has been chosen for the canister material due to its good corrosion resistance in anoxic water. However, colonization and activity of microbes on the surface or in the vicinity of the canister may initiate and accelerate several corrosion mechanisms. Bentonite buffer surrounding the canister is supposed to inhibit the migration of bacteria into the vicinity of the canister. Nevertheless, due to uneven saturation and swelling of the bentonite or formation of water-bearing fractures, the groundwater and microbes may come into contact with the canister. Here biotic and abiotic mesocosms were assembled containing copper coupons and an artificial groundwater at 10 °C under argon atmosphere. Sulfate reducing bacteria and methanogens enriched from the planned disposal site were added to the biotic experiments. During the exposure of one year, several electrochemical methods were performed intermittently. Preliminary results are presented and discussed in this paper. The results can be used when evaluating risks of the microbially induced corrosion of copper canisters.
INTRODUCTION
The Finnish nuclear waste disposal concept KBS-31 relies on the usage of multiple barriers that complement each other. These barriers include the form of the used nuclear fuel, the waste canister, consisting of a cast iron core with an outer copper capsule, the bentonite buffer, backfill materials in the tunnels and lastly the surrounding bedrock. Copper is chosen to serve as corrosion barrier for the disposal canister because of its assumed resistance to corrosion under anoxic conditions. The disposal canister plays a major part of the multi-barrier concept and should have a lifetime exceeding 100 000 years to prevent the release of radioactive nuclides to the surrounding environment.
