Corrosion Study of Actinide Waste Forms with Garnet-Type Structure
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Corrosion Study of Actinide Waste Forms with Garnet-Type Structure Sergey V. Yudintsev1, Anna A. Osherova1, Alexander V. Dubinin1, Alexander V. Zotov1, and Sergey V. Stefanovsky2 1 Institute of Geology of Ore Deposits, Staromonetny 35, 119017 Moscow, RUSSIA 2 SIA “RADON”, 7-th Rostovsky 2/14, 119121 Moscow, RUSSIA, [email protected] ABSTRACT Garnet-based ceramics doped with Gd, Th, and Ce as waste surrogates and compositions: (Ca1.5GdTh0.5)ZrFeFe3O12 (G3) and Ca2.5Ce0.5Zr2Fe3O12 (G21) were prepared at 1300 °C in air. Corrosion rates in deionized water measured using an MCC-2 procedure were found to be (in g × m-2 × day-1): 10-6 for Ce (G21), 3x10-5 for Gd and > Gd > Th. This is due to difference in chemical properties of these elements. Another explanation is that leach rate depends on bulk composition of the garnet matrix. The G3 sample, where both Fe3+ and Zr4+ ions occupy the same octahedral [B]6 sites, is more durable than the garnet in the G21 sample, in which the sites are filled with Zr4+ ions. XRD research (Urusov et al., personal communication) has shown that the first garnet, G3 - (Ca1.5GdTh0.5)(ZrFe)(Fe3)O12 possesses
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cubic symmetry, while the second, G21 - (Ca2.5Ce0.5)(Zr2)(Fe3)O12 has a distorted elementary cell with lowered symmetry to tetragonal. Table II. Cerium content in solutions, in ppb. Ce Initial solution: distilled water Initial solution: 0.01 M HCl Test period, days: 0 - 1 1 - 4 4 - 11 11 - 25 25 - 56 0 - 1 1-3 3 - 10 10 - 30 G21 (u) < dl 0,07 0,07 0,15 0,04 130,35 173,00 1222,00 10465,00 G21 (p) 0,07 0,08 0,16 0,07 0,08 54,79 58,30 448,00 6319,20 G21 (p) 0,25 0,20 0,16 0,15 0,07 17,03 20,60 304,70 4425,00 Blank-1 0,19 0,04 0,08 0,05 0,06 0,21 0,11 0,00 0,11 Blank-2 0,08 0,07 0,10 0,06 0,06 0,33 0,11 0,11 0,11 Table III. Thorium content in solutions, in ppb. Th Initial solution: distilled water Initial solution: 0.01 M HCl Test period, days: 0 - 1 1 - 4 4 - 11 11 - 25 25 - 56 0 - 1 1 - 3 3 - 10 10 - 30 G3 (u) 0,02 0,02 0,02 0,01 0,02 2,89 6,04 20,66 26,82 G3 (p) 0,1 0,02 0,03 0,04 0,03 2,81 4,11 37,31 88,71 G3 (p) 0,05 0,02 0,02 0,03 0,02 11,94 9,98 20,61 46,99 Blank-1 0,03 0,02 0,02 0,02 0,02 0,03 0,04 0,02 0,18 Blank-2 0,02 0,02 0,02 0,02 0,01 0,03 0,04 0,02 0,11 Table IV. Average concentration of the elements (10-7 mass %) in solutions for the tests with highest duration and their normalized leaching rates – in parentheses, g × m-2 × day-1. Sample Number Z2 PR G3 G21
Leachate: water Gd (30 days) Th (30 days) 1 (10-5) 2 (10-5) -5 3 (3 x 10 ) < 0.1 (< 10-6) Ce: 0.1 (10-6)
Leachate: 0.01 M HCl Gd (20 days) Th (20 days) 60 (2 x 10-3) 20 (3 x 10-4) 70 (4 x 10-3) 50 (10-3) Ce: 6300 (2 x 10-1)
CONCLUSIONS Garnet, A[8]3B[6]2X[4]3O12, is a prospective matrix for actinide-rich wastes with high content of corrosion products (Fe, Al, etc.). We have investigated chemical durability of two garnets, (Ca2.5Ce0.5)Zr2Fe3O12 and (Ca1.5GdTh0.5)(ZrFe)Fe3O12, using MCC-2 in water and 0.01 M HCl. For comparison the corrosion from the reference zirconolite Ca0.8Gd0.2ZrTi1.8Al0.2O7 and p
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