The nuclear industry in Sweden has through its waste management company SKB developed the KBS method for final disposal the high-level nuclear waste from nuclear power reactors. The method relies on the hypothesis that the nuclear waste can be kept isolated from the biosphere using man-made barriers of copper and clay. The barriers have to be tight for hundreds of thousands of years. The high-level waste in the form of spent nuclear fuel elements will be put in copper canisters surrounded by bentonite clay in mined tunnels at about 500 meters of depth in the bedrock. The surrounding bedrock contains flowing groundwater and the man-made barriers are to prevent the water from reaching the waste.
Copper corrodes in environments where oxygen is present. The process is easy to observe on copper roof materials that turn green from oxidation. When the industry’s KBS-method was developed in the 1970’s the understanding was that copper does not corrode at all in an anoxic (oxygen-free) environment in the bedrock. Later it has been shown that there are sulphide-producing bacteria in the bedrock that creates an environment that corrodes copper, but the nuclear waste company has tried to show that sulphide corrosion will not threaten a KBS repository for the time-scales involved. Thus the present long-term industry safety analysis for a KBS repository shows that the copper corrosion will only be the sulphide one and it is rather slow.
During the 1980's a researcher from the Royal Institute of Technology (KTH) in Stockholm, Gunnar Hultquist, presented new findings that showed that copper could corrode in environments without oxygen, as long as there is water present. The new findings were denied by the nuclear waste company SKB and ignored by the authorities. During the autumn of 2007 Gunnar Hultquist and a colleague Peter Szakálos presented the findings again, this time with more experimental results. This has caused a discussion about the KBS method in Sweden as the findings threaten basic assumptions underlying the long-term safety of the KBS method.
MKG has followed the issue closely since it re-appeared during 2007. The organisation has been reviewing the reports that the researcher from KTH, the authorities and the industry have been writing.
