Spectroscopic studies of transition-metal oxides, silicates, and pnictides: developing materials capable of sequestering nunclear waste

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With governments considering phasing out fossil fuel based power generators because of environmental concerns, nuclear energy is once again a serious alternative. Although the power generated by nuclear reactors is "clean", hazardous radioactive waste is produced. Canada supplies >25% of the worlds' uranium (U) supply (production value >$2.5 billion), with much of it destined for nuclear power facilities. To increase Canada's position in the U market, it is important to develop materials for use in the storage of nuclear waste. This waste can be sequestered in compounds that are densely packed and retard outward diffusion of the radioactive elements. The long-term goal of this research program is the development of ordered compounds that can sequester U in the structure and resist radiation induced structure damage. To initiate this research, model compounds representing host materials will be examined in order to gain a clear understanding of the relationship between crystal structure composition, bonding, electronic structure, and surface reactivity to the sequestration of actinides like U. In this program, pyrochlore ceramics (A2B2X6X'; A=Ca, Mn, Fe, rare-earths (RE); B=Ti,Nb,Ta; X/X'=O, F, OH), materials adopting the zircon (ASiO4; A=Zr, Hf) and zirconolite (A2B2O7; A/B=Ca, V, Zr, Ti, Hf) structures, amorphous silicates ([AO2]x[A'O2]y[SiO2]1-x-y; A/A'=Ti, Zr, Hf), and skutterudites (REM4Pn12; RE=La, Ce, Eu, Gd; M = Fe, Co; Pn (pnictide)=P, As, Sb, Bi) will be synthesized. The electronic structure and ability of these materials to be oxidized will be investigated by X-ray diffraction, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy, utilizing synchrotron radiation. Studying crystalline and amorphous silicates will allow for an examination of how radiation induced structure damage affects a materials ability to sequester U. (Many of the above materials also have applications in semiconductor devices, power generation, and refrigeration.) This research program is dedicated to applying X-ray spectroscopy to the study of the oxidation behaviour and changes in electronic structure with elemental substitution of the systems described above, so as to develop materials capable of sequestering nuclear waste.