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) above is color coded: Blue=Gadolinium (Gd), Gray=Zirconium (Zr), Red=Oxygen (O).

Worldwide, nuclear energy and weapons programs have created 1,350 metric tons of plutonium, an amount still growing by 70 metric tons annually. A major issue facing society is how to dispose safely of plutonium, which is radiotoxic and decays very slowly (it has a half-life of 24,500 years). One strategy is to immobilize it in chemically durable materials that absorb harmful neutrons and resist radiation damage. A 20-year collaboration between Rod Ewing at the University of Michigan and Bill Weber of Pacific Northwest National Laboratory has identified such materials. Using simulation techniques, they discovered that gadolinium zirconate materials resist radiation damage for millennia. These compounds absorb energy through the rearrangement of atoms within the crystal structure without becoming amorphous or structurally unstable—making them superior to the titanate materials being considered internationally for plutonium immobilization. (Plutonium-bearing titanates would degrade much faster.) The researchers also confirmed the mobility of the disturbed atoms and the ease of incorporating plutonium into the gadolinium-zirconate structure.

Scientific Impact: These studies demonstrated a systematic increase in radiation resistance as zirconium is substituted for titanium in gadolinium compounds. Discovery of these materials has stimulated research elsewhere, including Los Alamos National Laboratory, and led to identification of a phase that seems to be the best candidate for immobilizing plutonium.

Social Impact: This material offers a promising means of keeping future generations safe from the dual threats of radioactive contamination caused by plutonium decay, and the nuclear proliferation that might result from further use of the plutonium in weapons. Thus, this work may help resolve major dilemmas of the nuclear age.

Reference: S. X. Wang, B. D. Begg, L. M. Wang, R. C. Ewing, W. J. Weber, and K. V. Govidan Kutty, "Radiation Stability of Gadolinium Zirconate: A Waste Form for Plutonium Disposition," J. Materials Research 14 [12] (1999) 4470-4473.

W. J. Weber et al., "Radiation Effects in Crystalline Ceramics for the Immobilization of High-Level Nuclear Waste and Plutonium," J. Materials Research, 13 [6] (1998) 1434-1484.

W. J. Weber and R. C. Ewing, "Plutonium Immobilization and Radiation Effects," Science 289 (2000) 2051-2052.

B. D. Begg, N. J. Hess, D. E. McCready, S. Thevuthasan, and W. J. Weber, "Heavy-Ion Irradiation Effects in Gd2(ZrxTi1-x)2O7 Pyrochlores," J. Nuclear Materials 289 [1-2] (2001) 188-193.

URL: http://www.pnl.gov/energyscience/03-00/art1.htm

Technical Contact: Don Freeburn, Office of Basic Energy Sciences, 301-903-3156

Press Contact: Jeff Sherwood, DOE Office of Public Affairs, 202-586-5806

SC-Funding Office: Office of Basic Energy Sciences