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Hi, The CORE-CM Thursday Seminar this week is: *December 13:*/Rodney C. Ewing (/Joint appointments in: Earth & Environmental Sciences, Materials Science & Engineering, Nuclear Engineering & Radiological Sciences, University of Michigan. ) ///*"Actinide Structures for Nuclear Waste Storage: /The Road Not Taken" /*/President Obama recently appointed Professor Ewing Chair of the Committee to advise the DOE on issues related to storage of nuclear waste. /*//12-1pm BPS 1400: //*As usual Pizza will be available from 11:45am /Phil Duxbury ++++++++++++++++++++++++++ Abstract: During the past forty years, the materials science of nuclear waste forms has focused on the stability and long-term behaviour of nuclear waste glasses and used nuclear fuels, mainly UO_2 . During this same period, substantial quantities of Pu, now more than 2,000 metric tones, have accumulated, either still in the used nuclear fuel or chemically separated for weapons or energy applications. This "excess" plutonium, as well as associated "minor" actinides (Np, Am and Cm) offer a new, but seldom pursued, opportunity for the safe geologic disposal of transuranium elements. A variety of materials, with mineral analogues, including oxides, silicates and phosphates, have been investigated because of their high capacity to incorporate actinides, their chemical durability, and in some cases, their resistance to the radiation-induced transformation to the aperiodic state. There has been substantial interest in isometric pyrochlore, A_2 B_2 O_7 (A= rare earths, actinides; B = Ti, Zr, Sn, Hf), for the immobilization of actinides, particularly plutonium. Systematic studies of rare-earth pyrochlores have led to the discovery that certain compositions (B = Zr, Hf) are stable to very high doses of alpha-decay event damage. Three different processes have been observed: /i/) radiation-induced amorphization, /ii/) an order-disorder transformation and /iii/) phase decomposition. The radiation stability of these derivatives of the fluorite structure-type is closely related to the structural distortions caused by compositional variations that affect electronic structure and bond-type. Based on this very fundamental understanding of the radiation response, durable, actinide waste forms can be designed for specific temperature and radiation dose conditions, such as those found in very deep boreholes.^ 1 R.C. Ewing, W.J. Weber and J. Lian (2004) Pyrochlore (A_2 B_2 O_7 ): A nuclear waste form for the immobilization of plutonium and "minor" actinides. (Invited Focus Review) _Journal of Applied Physics_, vol. 95, 5949-5971.^ 2 F.X. Zhang, J.W. Wang, J. Lian, M.K. Lang, U. Becker and R.C. Ewing (2008) Phase stability and pressure dependence of defect formation in Gd_2 Ti_2 O_7 and Gd_2 Zr_2 O_7 pyrochlore. _Physical Review Letters_, vol. 199(4), 045503.^ 3 M. Lang, F.X Zhang, R.C. Ewing, J. Lian, C. Trautmann, and Z. Wang (*in press*) Structural modifications of GdZr_2-x Ti_x O_7 pyrochlore induced by swift heavy ions: Disordering and amorphization. _Journal of Mater. Res_.