Xiaoyan Shu

Preparation and heavy-ion irradiation effects of Gd2CexZr2−xO7 ceramics

A number of compositions with the general stoichiometry of Gd2CexZr2−xO7 (0 ≤ x ≤ 2) ceramics have been synthesized and received irradiation tests at room temperature with Xe20+ ions in a broad fluence range. X-ray diffraction (XRD) measurements shows that Gd2CexZr2−xO7 (0 ≤ x ≤ 0.2) samples adopt the pyrochlore structure, whereas Gd2CexZr2−xO7 (0.2 ≤ x ≤ 2.0) samples predominantly displayed an anion deficient fluorite structure, indicating that the structures of Gd2CexZr2−xO7 are determined by the content of doped Ce4+ ions. XRD results of irradiated samples (Gd2Zr2O7, Gd2Ce2O7) indicate that Gd2Zr2O7 was transformed into a radiation resistant anion deficient fluorite structure with increasing fluence, whereas the Gd2Ce2O7 was partially amorphized. It was found that the structural evolutions induced by irradiation are strongly dependent on the samples composition and ions fluence. In addition, SEM results show that the density and hardness of waste forms play an important role in the morphology modifications induced by irradiation. These results would be considered for design and elaboration of future matrices for actinide immobilization or transmutation.

Chemical stability of Ce-doped zircon ceramics: Influence of pH, temperature and their coupling effects

Abstract Zircon was employed to immobilize simulated tetravalentactinide nuclide (Ce4+). Zr1−xCexSiO4 (0≤x≤0.10) ceramics were synthesized and their chemical durabilities were investigated systematically. The effects of pH and temperature on the chemical durability of the as-prepared compounds were investigated using the MCC-1 static leaching test, and their coupling effects were also explored. It was found that the normalized release rates of Ce in deionized water and alkaline solutions (pH=10) were smaller than those in acid solutions (pH=4). At a certain pH value, the normalized release rate of Ce (LRCe) increased with the temperature in the initial period. However, the leaching progress almost reached a balance after 14 days, and both of the pH and the temperature had slight impact on the leaching of Ce element. Moreover, the LRCe were below 10−5 g/m2/d after 42 days, which was lower than those of other nuclear waste forms in all discussed leachates.

Microstructure and performance studies of (Mo, Ru, Pd, Zr) tetra-doped gadolinium zirconate pyrochlore

ABSTRACT Proper disposal of nuclear waste with multi-nuclides and multi-valence is still challenge. A series of (Mo, Ru, Pd, Zr) tetra-doped Gd2Zr2O7 ceramics were studied to understand the microstructure and performance evolution of nuclear waste forms that immobilised simulated waste after trialkyl phosphine oxides (TRPO) process. The structure of as-obtained samples were tested by X-ray diffraction, Raman, scanning electron microscope, electron back-scattered diffraction, and energy-dispersive X-ray spectroscopy, while the mechanical and chemical performance were characterised by Vickers hardness and aqueous leaching method. The results indicate that the mechanical behaviour are closely linked with the phase structure, and the highest Vickers hardness is obtained at the phase turning point. The leaching results show that the normalised leaching rate (LR) of the doped elements decrease in the order of Mo, Ru, Pd, Zr. After reaching equilibrium, their LR are as low as 4.12 × 10−4 g·m−2·d−1, 1.50 × 10−5 g·m−2·d−1, 1.30 × 10−5 g·m−2·d−1, and 2.09 × 10−7 g·m−2·d−1, respectively.

Chemical stability of simulated waste forms Zr 1– x Nd x SiO 4– x/2 : Influence of temperature, pH and their combined effects

Abstract The chemical stability of simulated waste forms Zr 1– x Nd x SiO 4– x /2 was investigated using the static leach test (MCC-1) with lixiviants of three pH values (pH=4, 6.7 and 10) at three temperature points (40, 90 and 150 °C) for periods ranging from 1 to 42 d, and the influence of temperature, pH, as well as their combined effects were explored in detail. The results showed that all the normalized release rate of Nd firstly decreased with leaching time and closed to equilibrium after 14 d. As the temperature increased, the normalized release rate of Nd also increased, but it was no more than 3×10 –5 g/(m 2 ·d). And, the normalized release rate of Nd reached the highest values (∼5×10 –5 g/(m 2 ·d)) when pH=4, whilst the normalized release rate of Nd remained the lowest value (∼1×10 –5 g/(m 2 ·d)) near neutral environment (pH=6.7).

Immobilisation of nuclear waste by microwave sintering with a natural magmatic rock

ABSTRACT A natural magmatic granite rock has been explored as a host matrix for nuclear waste disposal. The blank granite, in the form of a powder, was treated by microwaves in the temperature range 800°C to 1200°C. It was found that the amount of amorphous phase increased markedly with increasing temperature, which is promoted by the decomposing of feldspar (Na,KAlSi3O8) during the formation of a glassy network. Moreover, 16 wt.% of simulated nuclear waste, Nd2O3, could be successfully immobilised within the natural granite at a temperature of 1000°C. Nd3+ was found to exist both in the crystalline structure (as Nd2Si2O7) and in the bulk glass. This method of treating nuclear waste is simple and environmental friendly.

Heavy-ion irradiation effects on U 3 O 8 incorporated Gd 2 Zr 2 O 7 waste forms

In this research, the heavy-ion irradiation effects of U-bearing Gd2Zr2O7 ceramics were explored for nuclear waste immobilization. U3O8 was designed to be incorporated into Gd2Zr2O7 from two different routes in the form of (Gd1-4xU2x)2(Zr1-xUx)2O7 (x = 0.1, 0.14). The self-irradiation of actinide nuclides was simulated by Xe20+ heavy-ion radiation under different fluences. Grazing incidence X-ray diffraction (GIXRD) analysis reveals the relationship between radiation dose, damage and depth. The radiation tolerance is promoted with the increment of U3O8 content in the discussed range. Raman spectroscopy testifies the enhancement of radiation tolerance and microscopically existed phase evolution from the chemical bond vibrations. In addition, the microstructure and elemental distribution of the irradiated samples were analyzed as well. The amorphization degree of the sample surface declines as the U content was elevated from x = 0.1 to x = 0.14.

Rapid immobilization of simulated radioactive soil waste by microwave sintering

A rapid and efficient method is particularly necessary in the timely disposal of seriously radioactive contaminated soil. In this paper, a series of simulated radioactive soil waste containing different contents of neodymium oxide (3-25wt.%) has been successfully vitrified by microwave sintering at 1300°C for 30min. The microstructures, morphology, element distribution, density and chemical durability of as obtained vitrified forms have been analyzed. The results show that the amorphous structure, homogeneous element distribution, and regular density improvement are well kept, except slight cracks emerge on the magnified surface for the 25wt.% Nd2O3-containing sample. Moreover, all the vitrified forms exhibit excellent chemical durability, and the leaching rates of Nd are kept as ∼10-4-10-6g/(m2day) within 42days. This demonstrates a potential application of microwave sintering in radioactive contaminated soil disposal.