Crichtonite structure type (AM{sub 21}O{sub 38} and A{sub 2}M{sub 19}O{sub 36}) as a host phase in crystalline waste form ceramics
- Univ. of New Mexico, Albuquerque, NM (United States). Dept. of Earth and Planetary Sciences
- Chinese Academy of Sciences, Guiyang, Guizhou (China). Inst. of Geochemistry
Previous studies of ceramic crystalline waste forms, e.g. Synroc, tailored ceramics, and supercalcine, have concentrated on phases which are major constituents in the formulations: zirconolite, pyrochlore, hollandite, perovskite and zircon. These phases usually occur as members of multi-phase assemblages which are required for the incorporation of the wide variety of radionuclide elements present in the waste and the non-radioactive components added during reprocessing and pretreatment. The crichtonite structure (AM{sub 21}O{sub 38} and A{sub 2}M{sub 19}O{sub 36}), based on crystallo-chemical considerations and natural compositional analogues, may effectively incorporate both fission products and actinides. The naturally occurring crichtonite structure types include Sr (crichtonite), Ca and REE (loveringite), Na (landauite), REE and U (davidite), K (mathiasite), Ba (lindsleyite), and Pb (senaite), which are classified based on the dominant, large cations occupying the A-site. The crystal structure contains three types of sites of distinct size, from very large, M{sub 0}, intermediate (M{sub 1}, M{sub 3}, M{sub 4}, and M{sub 5}), to small (M{sub 2}). Numerous coupled substitutions within these cation sites allow for charge balance. Synthesis experiments were completed on the Ba-, Sr-, Ca-, and K-member compositions at 3 GPa and 1,150 C. Low pressure synthesis should be possible, as natural minerals mostly occur in low-P systems. Reaction products were characterized by powder X-ray diffraction, scanning electron microscopy and electron microprobe analysis. In addition to the crichtonite phases, rutile, spinel, perovskite and armacolite were identified as well. The Crichtonite structure type is estimated to accommodate waste loading of up to 30 wt. % PW-4B waste.
- OSTI ID:
- 382855
- Report Number(s):
- CONF-941075-; ISBN 1-55899-253-7; TRN: 96:025747
- Resource Relation:
- Conference: 18. international symposium on the scientific basis for nuclear waste management, Kyoto (Japan), 23-27 Oct 1994; Other Information: PBD: 1995; Related Information: Is Part Of Scientific basis for nuclear waste management 18. Part 2; Murakami, Takashi [ed.] [Ehime Univ., Matsuyama, Ehime (Japan). Dept. of Earth Sciences]; Ewing, R.C. [ed.] [Univ. of New Mexico, Albuquerque, NM (United States). Dept. of Earth and Planetary Sciences]; PB: 690 p.; Materials Research Society symposium proceedings, Volume 353
- Country of Publication:
- United States
- Language:
- English
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