Copper does not corrode in clean, oxygen-free water
Based on the results of the work of two separate teams of researchers, SKB (Svensk Kärnbränslehantering AB), the company responsible for final disposal in Sweden, has been able to confirm that copper does not corrode in clean, oxygen-free water. A very thin surface layer may corrode, but this does not have any significance for final disposal.
In addition, the tests did not reveal hydrogen formation similar to the results of the research team of the KTH Royal Institute of Technology, Stockholm, who brought up the issue of copper water corrosion. SKB has performed experiments using various grades of copper and different surface cleaning and treatment methods.
“The experiments performed in Gothenburg and Uppsala prove that copper does not corrode in clean, oxygen-free water. Therefore, this process does not have any significance for the final disposal of spent nuclear fuel”, says Allan Hedin, safety analyst at SKB.
SKB submitted the third situation report on the corrosion of copper in clean, oxygen-free water to the Swedish Radiation Safety Authority at the end of September. It presents new, important results concerning the controversial copper corrosion issue.
“We are relieved to hear about SKB's research results, as the question of copper corrosion is a significant part of the performance of the disposal canister,” says Marjut Vähänen, research and development manager at Posiva.
Posiva intends to perform an identical copper corrosion experiment at VTT to obtain additional confirmation for SKB's results and to ensure quality assurance of the experiments. The experiment is scheduled to start at the end of this year or the beginning of next year, and preliminary results are expected to be available at the end of 2015.
In addition, Posiva will commission studies into the impact of the properties of the canister surface on corrosion and, in particular, hydrogen formation, at the Tampere University of Technology next year.
“Posiva and SKB have for a long time conducted copper corrosion studies and exchanged information. We have been implementing both parallel and complementary research projects”, Vähänen says.
Years of research in the backgroundBehind this controversial issue is the observation of researchers from the KTH Royal Institute of Technology of hydrogen gas in connection with copper corrosion in clean, oxygen-free water. They have considered this as an indication that copper reacts with water, forming hydrogen, which is contrary to the common understanding in the field.
Since 2010, a research team of Ångströmlaboratoriet at Uppsala University has been requested to duplicate the earlier experiments.
In some studies, small amounts of hydrogen gas have been observed, for instance, when researchers have placed canister copper in clean, oxygen-free water. Thanks to the close cooperation of two laboratories, it has been possible to prove that the hydrogen previously observed with canister copper has been contained in the copper material from the start and is not the result of a corrosion process.
“The results we have now presented ultimately show that the copper canisters used for final disposal do not corrode in clean, oxygen-free water”, Hedin says.
Watch SKB's video about the copper corrosion studies on YouTube (in Swedish, Finnish subtitles)