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This issue...

  News in Brief

  View from the Inside

  Safer Plutonium Storage

  Crazy Physics

  Working Science

  People

  About

  Subscribe Free

New Rad-Resistant Material for Safer Plutonium Storage

by Rosalind Schrempf, Pacific Northwest National Laboratory

Gadolinium zirconium structure
Gadolinium zirconate is a highly radiation-resistant material that shows promise for use as a durable storage material for immobilizing plutonium and other actinides. The structure of gadolinium zirconate (Gd2Zr2O7) appears at left. Blue=Gadolinium (Gd), Gray=Zirconium (Zr), Red=Oxygen (O)


Plutonium-239 is a long-lived, fissile environmental contaminant with a half-life of 24,100 years, which decays to an even longer-lived fissile contaminant, uranium-235, with a half-life of 700 million years.

More than 1300 metric tons of plutonium generated by nuclear fuel cycles, including 100 metric tons of surplus weapons plutonium, exist worldwide and must be disposed of safely. One strategy for safe disposal is to trap the plutonium in a solid form and dispose of it in a geologic repository.

An international research team led by U.S.-based researchers Rodney Ewing of the University of Michigan (UM) and William Weber of the Pacific Northwest National Laboratory (PNNL) found that the material gadolinium zirconate is highly resistant to radiation and aqueous dissolution—both desirable properties in a storage material for plutonium and other actinides.

The researchers demonstrated that gadolinium zirconate resists radiation, unlike other possible crystalline ceramic hosts such as the structurally related gadolinium titanate. Both gadolinium titanate and gadolinium zirconate are effective neutron absorbers, which would be an advantage for plutonium disposal, and both are easily processed.

When exposed to radiation, the gadolinium titanates are affected by plutonium's alpha decay and amorphize, greatly increasing the rate of plutonium release in water. However, gadolinium zirconate, as processed in this research, was completely resistant to radiation, and its family members underwent only a minor change to a more stable crystal structure.

Research team members Bruce Begg (PNNL/Australia) and Govindan Kutty (UM/India) prepared a suite of pyrochlore samples from gadolinium titanate to gadolinium zirconate, with varying amounts of titanate to zirconate. Shixin Wang (UM) irradiated these samples and discovered that the gadolinium pyrochlores became increasingly resistant to radiation as the amount of zirconium they contained increased. The team monitored changes in the crystalline structure during irradiation using transmission electron microscopy and high-resolution electron microscopy.

These results (published in the December 1999 Journal of Materials Research) demonstrate that the performance of host materials for immobilizing plutonium can be improved significantly by changing their compositions from titanium-rich to zirconium-rich.

Other potential applications for the gadolinium zirconates include use as host material for immobilizing minor amounts of americium, neptunium, and curium at DOE sites and as electrolytes because of their fast ion conductivity.

This project was supported by the Office of Basic Energy Sciences/Division of Materials Sciences and Engineering.

Contact: William Weber, Pacific Northwest National Laboratory, bill.weber@pnl.gov; or Rodney Ewing, University of Michigan, rodewing@engin.umich.edu

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