Japan used seawater to cool nuclear fuel at the stricken Fukushima-Dai-ichi nuclear plant after the tsunami struck last March.
But Professor Alexandra Navrotsky of the University of California, Davis. and others have since discovered a new way in which seawater can corrode nuclear fuel, forming uranium compounds that could potentially travel long distances, either in solution or as very small particles.
“This is a phenomenon that has not been considered before,” said Navrotsky, distinguished professor of ceramic, earth and environmental materials chemistry. “We don’t know how much this will increase the rate of corrosion, but it is something that will have to be considered in future.”
Japan used seawater to avoid a much more serious accident at the Fukushima-Dai-ichi plant, and Navrotsky said, to her knowledge, there is no evidence of long-distance uranium contamination from the plant.
Uranium in nuclear fuel rods is in a chemical form that is “pretty insoluble” in water, Navrotsky said, unless the uranium oxidizes to uranium-VI — a process that can occur when radiation converts water into peroxide, a powerful oxidizing agent.
Peter Burns, professor of civil engineering and geological sciences at the University of Notre Dame and a co-author of a paper on the subject, had previously made spherical uranium peroxide clusters, rather like carbon “buckyballs,” that can dissolve or exist as solids.
In the paper, the researchers show in the presence of alkali metal ions such as sodium — for example, in seawater — these clusters are stable enough to persist in solution or as small particles even when they remove the oxidizing agent.
In other words, these clusters could form on the surface of a fuel rod exposed to seawater and then be transported away, surviving in the environment for months or years before reverting to more common forms of uranium, without peroxide, and settling to the bottom of the ocean. There is no data yet on how fast these uranium peroxide clusters will break down in the environment, Navrotsky said.