Nuclear fuel waste in long-term storage could form mineral phases that are not well understood, according to research by chemists at the University of Notre Dame and UC Davis and recently published in the journal Science.

Peter Burns, professor of civil engineering and geological sciences at Notre Dame, and graduate student Karrie-Ann Hughes, with UC Davis Interdisciplinary Professor Alexandra Navrotsky and postdoctoral researcher Katheryn Helean, studied the stability of two minerals, studtite and metastudtite, that contain both uranium and peroxide.

The researchers found that studtite and metastudtite may be readily formed on the surface of nuclear waste under long-term storage, possibly at the expense of other minerals, such as uranyl oxides and silicates, which have been more thoroughly studied and are better understood.

Studtites most likely form when radioactivity from uranium-rich rocks or nuclear fuel converts water to peroxide, which reacts with the minerals. Nuclear fuel waste under long-term storage, for example in the proposed Yucca Mountain depository in Nevada, would remain sufficiently radioactive to form studtite and metastudtite at the surface for thousands of years.

Not enough is known about these minerals to know if they will make radioactive wastes more stable or less, Navrotsky said.

"It means that the models used to assess fuel corrosion are incomplete. Whether the end result will be more or less corrosion than without studtite is a combination of thermodynamics and kinetics which needs to be explored further," she said.

Studtite also has been found on the surface of spent nuclear fuel stored at Hanford, Wash., nuclear site and on material at the site of the Chernobyl nuclear plant accident in Ukraine.

Uranyl peroxides must be considered in assessing the impact of uranyl materials on the release of radioactivity from nuclear waste in a depository, the researchers said. The study was published in the Nov. 14 issue of Science.