Corrosion poses risk in nuclear waste storage

Print edition : March 13, 2020

A nuclear waste storage facility in Idaho, United States. Photo: Dan Meyers on Unsplash

The materials the United States and other countries plan to use to store high-level nuclear waste are likely to degrade faster than previously thought because of the way those materials interact, new research from Ohio State University shows.

The findings, published in a recent issue of “Nature Materials”, show that corrosion of nuclear waste storage materials accelerates because of changes in the chemistry of the nuclear waste solution and the way the materials interact with one another. “This indicates that the current models may not be sufficient to keep this waste safely stored,” Xiaolei Guo, lead author of the study was quoted in the news release issued by the university.

The team’s research focussed on storage materials for high-level nuclear waste that is highly radioactive. While some types of the waste have half-lives of about 30 years, others like plutonium have a half-life that can be tens of thousands of years.

With no long-term viable nuclear waste disposal mechanism yet in operation, in most sites nuclear waste is stored near the plants where it is produced. While countries around the world have debated the best way to deal with nuclear waste, only Finland has started construction of a long-term repository for high-level nuclear waste.

In general, proposals involve mixing nuclear waste with other materials to form glass or ceramics and then encasing those pieces of glass or ceramics, now radioactive, inside metallic canisters. The canisters are buried deep underground in a repository to isolate it.

Researchers found that when exposed to an aqueous environment, glass and ceramics interact with stainless steel to accelerate corrosion, especially of the glass and ceramic materials holding nuclear waste. The study measured the difference between accelerated corrosion and natural corrosion of the storage materials. “In the real-life scenario, the glass or ceramic waste forms would be in close contact with stainless steel canisters. Under specific conditions, the corrosion of stainless steel will go crazy,” he said. “It creates a super-aggressive environment that can corrode surrounding materials.”

To analyse corrosion, the research team pressed glass or ceramic “waste forms” (the shapes into which nuclear waste is encapsulated) against stainless steel and immersed them in solutions for up to 30 days, under conditions that simulate those under Yucca Mountain, the proposed nuclear waste repository in the U.S.

Those experiments showed that when glass and stainless steel were pressed against one another, stainless steel corrosion was “severe” and “localised”. The researchers also noted cracks and enhanced corrosion on the parts of the glass that had been in contact with stainless steel.

Part of the problem lies in the Periodic Table. Stainless steel is made primarily of iron mixed with other elements, including nickel and chromium. Iron has a chemical affinity for silicon, which is a key element of glass.

The experiments also showed that when ceramics, another potential holder for nuclear waste, were pressed against stainless steel under conditions that mimicked those beneath Yucca Mountain, the ceramics and stainless steel corroded in a “severe localised” way.

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