The Swedish nuclear waste company SKB has published a report from the 20-year old LOT experiment with copper and clay in the Äspö Hard Rock Laboratory at the Oskarshamn nuclear power plant. In the report (SKB TR-20-14), the company presents analyses and interpretations of the results regarding copper corrosion and compares them with results from previous experiments and with model calculations. Miljöorganisationernas kärnavfallsgranskning MKG (The Swedish NGO office for Nuclear Waste Review) has made an initial analysis of the report and finds it scientifically inferior, but it is still clear that copper corrodes so much in a nuclear fuel repository environment that the metal cannot be used as canister material. The Swedish Radiation Safety Authority's SSM's quality assurance can now be started in earnest, and it is very much needed. MKG has submitted comments as a contribution to SSM's review work, including the issue of the importance of when the experiment packages became anoxic.
The nuclear waste company's SKB's first report (SKB TR-20-11) on the uptake of two test packages in the LOT experiment in the autumn of 2019 was published on 15 June 2020. The report describes the installation of the test packages and the retrieval, and reports data for the experiment during the 20 years it been in operation, including temperatures and water conditions in the bentonite clay surrounding the copper components. The second report from the experiment (SKB TR-20-14), that contains the results of the copper corrosion studies, has now been published by the nuclear waste company.
The two test packages were secretly taken up by the nuclear waste company in the autumn of 2019. When this was revealed the company did not want to report any copper corrosion results until after the government had approved the licence to start building the repository for spent nuclear fuel in Forsmark. The company then changed its mind and said that copper corrosion results would be reported both for the copper pieces (coupons) that were in the test packages, but also for the central copper tube that has been heated to significantly higher temperatures. The Swedish Radiation Safety Authority SSM then decided to start a project to ensure that the copper corrosion results that the company reports will be quality assured.
MKG and its member organizations are convinced that the copper corrosion results from the two 20-year old LOT packages can provide important information for the government's ongoing review of license application for the planned spent nuclear fuel repository in Forsmark. MKG has made an initial analysis of the second SKB report with the copper corrosion results. The report has serious scientific shortcomings, but still shows that copper in a repository environment corrodes strongly even in the absence of oxygen and also with pitting. Since the test packages were filled with anoxic (free from oxygen gas) groundwater from a hole drilled in the bedrock before heating began, most of the extensive corrosion that is seen must have taken place in oxygen-free conditions. According to the nuclear waste company this should not be possible.
MKG has also observed that the company has not dared to report images and metallographic cross-sections on the surfaces of the copper tube that have been heated most, i.e., in the middle of the lower part of the tubes. If the report was to be scientifically sound this should be reported as this is where the largest corrosion has occurred and pitting is greatest. Instead, only pictures of the pieces of pipe that lie in the middle of the pipe (at clay blocks 21-23) are shown, i.e., just above the lower half of the pipe. It is at the clay blocks 9-12 that the largest corrosion on the pipe must be investigated. The grounds that the largest corrosion is not investigated properly means that the report can be rejected as not scientific, and the government should be able to make a decision not to allow the nuclear fuel repository.
In addition, the images shown in the report are consistently of such low resolution that they cannot be studied in detail. But even more serious is that it is not possible to trace where the cross-section images come from on the copper pieces or on the piece of central pipe that has been analysed. Thus, there is no possibility of knowing whether the images show the largest corrosion or not. However, MKG believes that this may not so important as there is so much documented corrosion with pitting that should not occur at all, so that it is obvious that copper does not function as a canister material. But it is a general problem that the traceability of the results in the report is so low.
MKG is of the impression that the report has been finally edited by the main author from SKB. The question must be asked whether so-called "Cherry-picking" has been used when choosing the pictures to include? Hopefully there is better scientific integrity in the reports from the research labs at Rise Kimab and Swerim that have sent to SKB.
The nuclear waste company SKB claims on its website that all results are completely expected and that the severe corrosion attacks are caused by oxygen that has been trapped in the experimental packages. MKG is of the understanding that this is a completely unreasonable explanation. Since the experimental packages before heating started were filled with oxygen-free water from a special pipe that took water from the surrounding rock, the whole experiment, except for the clay part, had no oxygen in it after the heating started. There has thus been oxygen-free water closest to all copper surfaces on the pipe and the oxygen that is originally present in the clay has been consumed in a few months and has also not been able to reach the copper pipe without being consumed by bacteria.
MKG wants the nuclear waste company to report traceable results of the corrosion on the most heated parts of the copper pipe. This has been the stated opinion of MKG and its member associations for a long time and is the most natura thing to do in scientific work. Of particular interest is also to report in more detail the severe corrosion that has taken place on the bottom plates that have stood against sand. The water in the sand has certainly been oxygen-free almost from the very beginning and the extensive corrosion cannot be explained away by the nuclear waste company. A strange phenomenon that the company also has to explain is why the inner copper surface of the pipe in the middle of the experiment is so unaffected and shiny, while at the bottom of the pipe there is a lot of corrosion. The inside of the pipe has been in contact with oxygen in air but the corrosion seems much lower than that which has taken place on the outside of the pipe which has been in contact with oxygen-free water.
A link to an article on MKG:s Swedish web site with the report is below.
The Swedish Radiation Safety Authority SSM will now be able to seriously begin its work to ensure the quality of the results and has hired consultants from the British company Galson Sciences to provide support in the work. Because the report has such serious shortcomings and so many questions can be asked about the report, this work is really needed. See the link to the separarate news article about the SSM review, and the MKG input to the review below. There a link can also be found to all the SSM documents in the review.
MKG believes that SSM should already now see that the nuclear waste company is not seriously interested in reporting the corrosion results from the 20-year trial packages, which gives a clear signal that the company knows that the copper canister will not work as intended. As an important consultative body to the government prior to the admissibility decision on the nuclear fuel repository, the authority should be prepared to now reconsider its support for the project.
News article on the MKG Swedish web pages about the SKB LOT corrosion report, 201001 >>
News article in English about the SSM review, 2011XX >> (coming soon)
See also the following news articles on MKG:s English pages:
Östhammars community tells the government they accept the repository for spent fuel, 201013 >>
SKB will publish LOT project results and SSM will do a quality control 200325 >>
SKB sends complementary information on copper corrosion to the government 190404 >>
