Development of Matrix for the Immobilization of High Level Radioactive Waste : Study on the Synthesis of Ce-pyrochlore

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(1) , 35, 2 , 97-102, 2002 Econ. Environ. Geol., 35(2), 97-102, 2002.

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(5) . . . . . Development of Matrix for the Immobilization of High Level Radioactive Waste : Study on the Synthesis of Ce-pyrochlore Soo-Chun Chae1*, Youn-Nam Jang1, In-Kook Bae1 and Yudintsev, S.V2 1. Department of Geology Division, Korea Institute of Geoscience and Mineral Resources, Taejon 305-350, Korea Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry. 2. Ce-pyrochlore (CaCeTi2O7) was synthesized to study its properties and phase relations in CaO-CeO2-TiO2 system because Ce-pyrochlore was known as a promising material for the immobilization of radioactive actinide. The samples were prepared from the high purity starting materials under the pressure of 200~400 kg/cm2 at room temperature, and annealed at 1000~1500oC. The Synthesized samples were analysed and identified with XRD and SEM/EDS methods. The optimal formation condition of Ce-pyrochlore was at 1300oC under O2 atmosphere and the chemical composition of it was Ca1+xCe1-xTi2-yO7-x-2y (x=0.03~0.05, y=0.02~0.04). At temperature between 1300~ 1400oC, Ce-pyrochlore underwent rapidly the incongruent decomposition to perovskite. Ce-perovskite, a partial solid solution between perovskite and loparite (Ce0.66TiO3), was observed as a major phase above 1400oC.. pyrochlore, perovskite, immobilization, incongruent, loparite.

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(73) 3. ). ). . !'00 . . !(00 =?. Scanning electron microphotograph of samples sintered at 1300oC.. XRD patterns of Ce-pyrochlore and Ce-perovskited wich are sintered at (a) 1300oC and (b) 1400oC.. Scanning electron microphotograph of sample sintered at 1500 oC..

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(76) Chemical compositions of Ce-pyrochlore and Ce-perovskite. Heating No.. Temp.. hours. Under air atm. LGZ-73 1200 (air) LGZ-62 1300 (air) LGZ-96 1400 (air) LGZ-21 1450 (air) LGZ-15 1500 (air) LGZ-81 (air). 1500. Chemical composition*. 20 20 20. Composition. Ce-Perovskite. Ce/Ti. Ca/Ti. Ce/Ca. Composition. Ce/Ti. Ca/Ti Ce/Ca. Ca1.01Ce0.83Ti2.06O6.8 Ca1.02Ce0.79Ti2.1O6.8 Ca1.01Ce0.96Ti1.94O6.8 Ca0.98Ce0.95Ti1.97O6.8 Ca1.06Ce0.88Ti1.99O6.8 Ca1.04Ce0.87Ti2.01O6.8. 0.40 0.37 0.49 0.48 0.44 0.43. 0.49 0.50 0.52 0.49 0.53 0.51. 0.82 0.77 0.95 0.97 0.83 0.84. Ca0.84Ce0.15Ti0.97O3. 0.15. 0.87. 0.18. Ca0.7Ce0.24Ti0.97O3 Ca0.66Ce0.27Ti0.97O3 Ca0.57Ce0.32Ti0.98O3 Ca0.57Ce0.31Ti0.98O3 Ca0.55Ce0.32Ti0.98O3 Ca0.56Ce0.33Ti0.98O3 Ca0.55Ce0.33Ti0.97O3 Ca0.54Ce0.34Ti0.97O3 Ca0.56Ce0.33Ti0.97O3 Ca0.57Ce0.33Ti0.96O3 Ca0.56Ce0.33Ti0.97O3. 0.25 0.28 0.33 0.32 0.33 0.34 0.34 0.35 0.34 0.34 0.34. 0.72 0.68 0.58 0.58 0.56 0.57 0.57 0.56 0.58 0.59 0.58. 0.34 0.41 0.56 0.54 0.58 0.59 0.60 0.63 0.59 0.58 0.59. Ca1.04Ce0.87Ti2.01O6.8. 0.43. 0.51. 0.84. Ca1.05Ce0.94Ti2.04O7 Ca1.03Ce0.99Ti2O7 Ca1.07Ce0.97Ti1.99O7 Ca1.04Ce0.98Ti1.99O7 Ca1.06Ce0.97Ti2O7 Ca1.01Ce0.98Ti2.01O7 Ca1.02Ce0.99Ti2O7 Ca1.06Ce1.01Ti1.96O7. 0.46 0.49 0.48 0.49 0.48 0.48 0.49 0.51. 0.51 0.51 0.53 0.52 0.53 0.50 0.51 0.54. 0.90 0.96 0.91 0.94 0.92 0.97 0.97 0.95. Ca0.87Ce0.14Ti0.96O3 Ca0.85Ce0.13Ti0.97O3. 0.15 0.13. 0.91 0.88. 0.16 0.15. Ca0.81Ce0.18Ti0.96O3 Ca0.81Ce0.17Ti0.97O3 Ca0.78Ce0.2Ti0.96O3 Ca0.74Ce0.22Ti0.96O3 Ca0.76Ce0.2Ti0.97O3. 0.19 0.18 0.21 0.23 0.21. 0.84 0.84 0.81 0.77 0.78. 0.22 0.21 0.26 0.30 0.26. 5 5. 48. Under O2 atm. LGZ-77 1200 20 (O2) LGZ106 1270 40 (O2) LGZ128 (O2) LGZ109 (O2). Ce-pyrochlore. 1300. 20. 1350. 40. *Chemical compositions were analysed by EDS.. F )x)2y2@ l )×2É\Ø)ZM 2 3°q ?> 2 ! Ö G < 2

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