In the final repository, the canister must be protected against corrosion.  Above all oxygen and sulphide ions (S2-) of the substances, which are present in the groundwater, can cause corrosion of the canister. Oxygen can react with copper and form copper oxides. The sulphide ions form copper sulphide when they react with the copper.

Oxygen is the bacteria's favourite dish and the substance that is consumed first. The water absorbed by the bentonite buffer will contain very little oxygen.

Great transport resistance
In an attempt to figure out what happens during the sulphide attacks on the canister, scientists have postulated two scenarios.

• In the first scenario
  
  • The SRB grew in the rock just outside the bentonite buffer. The bacteria produced hydrogen sulphide, which then passed very slowly in through the layer of bentonite. But the bentonite proved to offer so much transport resistance that the influence of the hydrogen sulphide on corrosion was largely negligible.
• In the second scenario
  
  • The SRB strains grew inside the bentonite instead of in the rock outside. However, experiments in the laboratory showed that the water content of the bentonite was too low. A small portion of the bacteria were able to survive as long as two months. The rest died almost immediately.
  Information from- http://www.skb.se/