Li Yifan,Cao Shuang,Yang Qingming,Wang Yuannuo,Wang Jingyang,Jiao Caishan,Zhang Meng,Zhang Lei
The removal of Cs and Sr from high level radioactive waste is very important for ecological protection. However, simultaneous immobilization of Cs and Sr is rarely reported. In this work, a perovskite structure CsSr 2 Ta 3 O 10 was synthesized by molten salt method. CsSr 2 Ta 3 O 10 has good thermal stability up to 900 °C at least. Under the γ irradiation of Co-60, most of the material maintained its structural integrity. CsSr 2 Ta 3 O 10 demonstrates a wide range of pH durability, where Cs is stable in the pH range from 4 to 12 and Sr from 2 to 12. Its frame structure remains stable in the pH range from 2 to 12 and will not be decomposed. Further sintering of CsSr 2 Ta 3 O 10 ceramic waste forms results in a high density of 93% − 95%. Moreover, leaching experiments conclude that the long-term leaching rates of Cs and Sr begin to stabilize after 14 days, reaching the order of 10 0 and 10 −3 g·m −2 ·d −1 . These results provide a possibility for the simultaneous immobilization of Cs and Sr.
Hong Zhang,Qian Du,Xin Du,Zhanglian Xu,Shaoqiang Guo,Wentao Zhou
The electrorefining of spent nuclear fuels in a molten LiCl-KCl salt electrolyte recovers the valuable actinides but also releases radioactive fission products in the salt. To minimize the nuclear waste volume, dissolved fission products such as rare earths (REs) must be removed from the electrorefining salt and immobilized into proper wasteforms. Here we propose a two-step approach for treating the electrorefining waste salt by (i) the electrolytic recovery of REs from the salt using a liquid metal cathode; and subsequent (ii) oxidative extraction of REs from the liquid metal into durable wasteforms. Experimental demonstration using rare earth element samarium (Sm) and liquid metal (Bi) was successful. The Sm ions dissolved in the salt can be selectively recovered as dendrite Sm-Bi intermetallic products on the top of liquid bismuth cathode through electrolysis at appropriate applied currents or potentials. Then the Sm in the Sm-Bi alloy was efficiently extracted into both zinc-in-titania (ZIT) glass ceramic and lanthanide aluminoborosilicate (LABS) glass wasteforms through selective oxidation at Sm 2 O 3 loadings of 18–25 wt% and 50 wt%, respectively. Recycling of the electrorefining salt with minimum nuclear waste generation is foreseeable with the use of this simple, efficient, and highly compatible process.
The garnet structure is a promising solid material for nuclear waste because it can contain all kinds of actinides. Yttrium iron garnet Y 3 Fe 5 O 12 (YIG) is the model component of this kind of substitute. In this study, Nd-doped YIG ceramic samples were prepared by microwave sintering at different sintering temperatures (1100 °C, 1200 °C, and 1300 °C) for different sintering time (0.5 h, 2 h, 4 h, and 6 h). The effects of synthesis temperature and sintering time on the solubility and microstructure of Y 3-x Nd x Fe 5 O 12 (0 ≤ x ≤ 3.0) were evaluated. The X-ray diffraction (XRD), scanning electron microscopy (SEM) and backscattering scanning electron microscopy (EBSD) results show that single phase garnet structure can be synthesized and enhanced solubility of Nd in YIG was found at higher temperatures. The solubility of Nd in garnet is 50 mol% (x = 1.5) and 60 mol% (x = 1.8) at 1200 °C and 1300 °C, respectively. There is no significant dependence of the solubility on sintering time. The SEM analysis and Archimedes drainage test show that the relative density of Y 1.2 Nd 1.8 Fe 5 O 12 ceramics is 88.15% and 99.94% at 0.5 h and 6 h, respectively, indicating dense YIG could be obtained with a relatively long sintering time. The results show that microwave sintering can rapidly and efficiently synthesize the YIG ceramic samples.
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