Immobilizing Behavior of Trivalent Actinide Nuclides by YIG Ceramics

doi:10.15541/jim20210669

Abstract

Abstract:

Garnet is considered as a potential matrix for immobilizing high-level radioactive waste (HLW) because of its large actinide package capacity and chemical flexibility. Y_3-_xNd_xFe₅O₁₂ (0≤x≤2) series yttrium iron garnet (YIG) samples was successfully synthesized by solid-state sintering method using Nd³⁺ to simulate trivalent actinides. The solubility limit of Nd in the YIG and the influence of Nd doping amount on the phase and microstructure of ceramics was studied. Then the chemical durability of Nd-doped yttrium iron garnet solidified body under different pH conditions was evaluated. The results show that the ceramics with x≤1.7 show homogeneous single YIG, but the ceramics with x≥1.8 exhibit coexistence of three crystal phases (YIG, NdFeO₃ and Fe₂O₃). The solubility limit of Nd³⁺ in the pure YIG is about 29.5% (in mass). As the amount of Nd doping increases, the density of the ceramics increases, the volume decreases, and the porosity decreases. The leaching experiment results show that the normalized leaching rate of the elements (LR_i) is 10^-6~10^-5g·m^-2·d^-1. LR_Y is smaller than LR_Nd, and the normalized leaching rate of the elements in acid leachate is slightly higher than those in neutral and alkaline leachates. The results indicate that YIG ceramics are a potential candidate form for trivalent actinides.

Key words: yttrium iron garnet (YIG), actinide, phase evolution, chemical stability

CLC Number:

TQ174

LUO Shilin, ZHANG Shengtai, XU Baoliang, WANG Lingkun, DUAN Siyihan, DING Yi, ZHAO Qian, DUAN Tao. Immobilizing Behavior of Trivalent Actinide Nuclides by YIG Ceramics[J]. Journal of Inorganic Materials, 2022, 37(7): 757-763.

Figures/Tables 8

Fig. 1 XRD pattern of (a) Y3-xNdxFe5O12 (0≤x≤2.0, large gradient) and (b) Y3-xNdxFe5O12 (1.7≤x≤2.0, small gradient)

Fig. 2 Variation trend of lattice parameter of Y3-xNdxFe5O12 (0≤x<2) with Nd amount

Fig. 3 SEM images of Y3-xNdxFe5O12 (0≤x≤2) when (a) x=0, (b) x=0.5, (c) x=1.5, (d) x=2.0, and (e, f) EDS analyses of corresponding spots in (d)

Fig. 4 EDS elements mappings of the sample x=1.5 Colorful figures are available on website

Fig. 5 (a) Density and linear shrinkage, (b) relative density and open porosity of Y3-xNdxFe5O12 (0≤x≤2)

Fig. 6 Normalized release rates of (a) Y and (b) Nd in Y1.5Nd1.5Fe5O12 ceramics in the leaching solution with different pH

Table 1 Normalized release rates of several different garnets

Material	Normalized release rate/(g·m^-2·d^-1)	Ref.
Ca_1.59Gd_1.01Ce_0.45Zr_1.14Fe_0.77Fe_3.03O₁₂	10^-6-10^-3	[7]
LuAG, YAG	10^-5-10^-4	[28]
(Ca_1.5GdTh_0.5)(ZrFe)(Fe₃)O₁₂	10^-6-10^-3	[29]
Ce-doped YIG	10^-5-10^-4	[30]
YIG	10^-6-10^-5	In this work

Fig. 7 SEM images of Y1.5Nd1.5Fe5O12 ceramics after leaching (a) pH 3; (b) pH 7; (c) pH 11

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