Xirui Lu

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.

Facile route to synthesize mesoporous SBA-15 rods with different sizes for lysozyme immobilization

Lysozyme has been successfully immobilized in the mesoporous channels of SBA-15 rods with different sizes. In order to clarify how SBA-15 rods sizes affected the immobilization behavior of lysozyme, small-angle X-ray powder diffraction, Fourier-transformed infrared spectra and nitrogen adsorption/desorption were employed to characterize the SBA-15 rods before and after immobilization. The results clearly showed that lysozyme was immobilized into the channels of SBA-15 rods and the well ordered mesoporous structure of SBA-15 after adsorption of lysozyme was retained. The rate and amount of immobilization were strongly dependent on rods sizes. It was found that the rate and amount of lysozyme immobilization increased with decreasing the sizes of SBA-15 rods. The SBA-15 rods with small size exhibited rapid (<20 min to reach equilibrium) and high-capacity (up to 835 mg g−1) lysozyme immobilization. The effect of SBA-15 rods sizes on lysozyme immobilization rate and amount was discussed in detail. Furthermore, a mechanism for the effect of the rods sizes on the immobilization behavior was suggested.Graphical Abstract

Vitrification of radioactive contaminated soil by means of microwave energy

Simulated radioactive contaminated soil was successfully vitrified by microwave sintering technology and the solidified body were systematically studied by Raman, XRD and SEM-EDX. The Raman results show that the solidified body transformed to amorphous structure better at higher temperature (1200 °C). The XRD results show that the metamictization has been significantly enhanced by the prolonged holding time at 1200 °C by microwave sintering, while by conventional sintering technology other crystal diffraction peaks, besides of silica at 2θ = 27.830°, still exist after being treated at 1200 °C for much longer time. The SEM-EDX discloses the micro-morphology of the sample and the uniform distribution of Nd element. All the results show that microwave technology performs vitrification better than the conventional sintering method in solidifying radioactive contaminated soil.

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.

Self-propagating high-temperature synthesis, phase composition and aqueous durability of Nd–Al bearing zirconolite-rich composites as nuclear waste form

ABSTRACT In this study, the zirconolite-rich composite was rapidly synthesised from self-propagating high-temperature synthesis plus quick pressing using MoO3 as the oxidant and Ti as the reductant. As a surrogate of trivalent actinides, Nd was introduced to substitute the Ca site of zirconolite and Al was employed as the charge compensator to replace the Ti site (nominally Ca1−xNdxZrTi2−xAlxO7). The phase composition and Nd occupancy were analysed after Nd2O3 addition. Nd-bearing zirconolite was produced as the major ceramic phase. Nd mostly substitutes the Ca sites of zirconolite, which results in waste loading higher than 8.6 wt-% Nd. The aqueous durability of Nd–Al codoped sample (with 15 at.-% Nd substitutes the Ca site of zirconolite) was evaluated at 90°C as well. The 42 days normalised leaching rates of Mo, Ca and Nd were measured to be 3.70, 1.90 × 10−2 and 3.46 × 10−4 g m−2 d−1.

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.