Corrosion resistance of disposal canister
The canister plays an important role in the final disposal of spent nuclear fuel. The massive interior of the canister, manufactured from spheroidal graphite cast iron, makes the canister mechanically strong. A five-centimetre thick copper cladding protects the inner part and the canister from corrosion.
Posiva and its Swedish cooperation partner SKB (Svensk Kärnbränslehantering Ab) have studied the behaviour of copper in conditions similar to the deep repository for decades. The results show that the pure oxygen-free copper that has been selected as the cladding material will efficiently withstand corrosion in the oxygen-free environment of the bedrock.
However, researchers of the Royal Institute of Technology (Kungliga Tekniska Högskolan, KTH) in Stockholm have estimated that copper could corrode fairly quickly also in oxygen-free environment. This view is based on the theory that copper deprives oxygen from water molecules, which will lead to corrosion and the generation of hydrogen gas.
The Swedish Radiation Authority SKI requested its BRITE expert group to study the results published by the KTH researchers in the summer of 2008. The expert group came to the conclusion that the data presented by the KTH researchers on their experiments does not offer sufficient proof about the proposed corrosion mechanism, and no other studies of the sector support the claims made. The BRITE group proposes independent tests to study the accuracy of the claims.
Posiva is in favour of the proposal on independent testing but will also study itself the accuracy of the KTH researchers’ claims and their possible impact on long-term safety of final disposal. In the autumn of 2009, Posiva and SKB will start joint research attempting to reproduce the KTH researchers’ tests and find out whether or not the results will be similar. VTT Technical Research Centre of Finland will be in charge of the research implementation.