Rethinking Zircon For Nuclear Waste

Plans for using ceramics made of the mineral zircon (ZrSiO₄) to store hazardous ²³⁹Pu nuclear waste may have hit a dead end. A new study suggests that zircon is far more susceptible to the damaging effects of α radiation than originally thought; the finding presents a problem for zircon's use in long-term storage of ²³⁹Pu, an α-emitter with a 24,110-year half-life (Nature 2007, 445, 190). Ian Farnan of the University of Cambridge and Herman Cho and William J. Weber of Pacific Northwest National Laboratory came to that conclusion when they used NMR spectroscopy to assess how much damage occurs to zircon when it's doped with ²³⁹Pu and the shorter lived ²³⁸Pu. They found that each α-decay event displaces about 5,000 atoms, far more than the 1,000-2,000 displacements predicted by standard simulations. That rate of decay would render zircon containing 10% ²³⁹Pu by weight an amorphous material after only 1,400 years-far less than the 250,000-year time scale desired.