There's An Unexpected Problem With Plans For Storing Nuclear Waste

Yucca Mountain, Nevada, was chosen as the site for the United States to store all its high-level nuclear waste. That plan has stalled, and if it ever restarts it will have to reckon with one problem no one anticipated. Public Domain

The materials in proposed high-level nuclear waste storage facilities will interact in ways that were not predicted, speeding up corrosion and raising the risk of radioactive release. The problems are probably solvable, but the cost of doing so is unknown.

Although the details vary, plans to store the most radioactive nuclear waste usually have some common features. Initially the waste is to be held at a temporary, above ground, facility until enough short-lived radioactive isotopes decay to make processing safer. Then the waste will be mixed with suitable materials to form borosilicate glass or ceramic, which will be placed inside metal containers and buried in deep, and preferably remote, facilities.

Metal containers will eventually be worn away by water, but it has been hoped sufficiently dry sites will hold the waste for the timescales required for radioactivity to die down. Dr Xiaolei Guo has called that into question, providing evidence everything could break down a lot faster than previously anticipated.

The problem Guo reports in Nature Materials lies where the metal meets the glass or ceramic. When water is present, stainless steel interacts with either proposed waste encapsulator to speed corrosion. In a trial, Guo found cracks appeared in the radioactive glass within just 30 days when steel containers were pressed against their contents, a problem when these are meant to last for thousands of years. Ceramics also corroded as well, and affected the steel into the bargain.

"This indicates that the current models may not be sufficient to keep this waste safely stored," Guo said in a statement. The claim might be dismissed if Guo was trenchantly opposed to nuclear power. Instead, he is based at Ohio State University's Center for Performance and Design of Nuclear Waste Forms and Containers.

Schematic of a stainless steel nuclear waste canister, with radioactive particles (purple) trapped inside in glass and the acidic spiral that starts when water, steel, and glass are brought together. Guo et al/Nature Materials

Guo attributes the problems to the affinity of iron to silicon, which combined with saltwater leads to a highly acidic local environment. Previous studies have missed this because they looked at the storage components independently, rather than considering their interactions.

Iron-free containers may solve the problem, or perhaps barriers can be placed between the steel and glass. However, following the discovery rock salt domes – popular as proposed storage sites – are more susceptible to water intrusion than suspected the findings demonstrate a safe disposal method for high-level nuclear waste is still some way off, and budgets may be insufficient.

So far, not much has come of long-term storage plans, in large part because people living near the proposed storage locations don't tend to like the idea a great deal. The Yucca Mountain facility was the United States' chosen site, but being in Nevada, a swing state for presidential and Senate elections, has given opponents the clout to bring development to a standstill. Finland is the only nation to have begun constructing a long-term high-level waste repository.

 

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