耐事故燃料芯块的制备方法与研究进展

福岛核事故发生后,为提高核燃料元件抵抗严重事故能力而开发的耐事故燃料成为核行业研究热点。本文介绍了以BeO、SiC掺杂为代表的热导增强型UO₂芯块、高铀密度高热导燃料芯块和全陶瓷微封装燃料芯块,总结了耐事故燃料芯块的优势特性、热导率、制备方法和研究进展,分析和展望了耐事故燃料芯块的现有问题和应用前景,以期为耐事故燃料芯块的研究提供参考。     

Corrosion of New Zirconium Claddings in 500 °C/10.3 MPa Steam: Effects of Alloying and Metallography

With the aim of improving corrosion resistance of rod cladding for in-service and accident conditions, six new zirconium alloys (named N1-N6) have been designed. The contents of Sn and Nb were optimized for better behavior at high-temperature pressurized water, and Fe, Cr, V, Cu or Mo elements were added to the alloys to adjust the corrosion behavior. The current work focused on the rapid corrosion behavior in 500 °C/10.3 MPa steam for up to 1960 h, aiming to test the corrosion resistance at high temperature. The structure of matrix and properties of second-phase particles (SPPs) were characterized to find the main differences among these alloys. All the six alloys exhibited better corrosion resistance than N36, and N1 was shown to have the best performance. A careful analysis of the corrosion kinetics curves revealed that Cr was beneficial for severe condition. Elements Fe, Cr, V, Cu or Mo aggregated into SPPs with different concentrations and structures. This was demonstrated to be the main reason for different corrosion resistance. Due to good processing control, all alloys had a uniform structure and a uniform distribution of SPPs. As for N4, N6 and N36, the existing of large-size SPPs (450 nm) might be a contributing factor of the relatively poor corrosion resistance.     

Meso-scale analysis of the creep behavior of hydrogenated Zircaloy-4

During dry storage, creep is the most likely degradation mechanism for spent Zircaloy fuel cladding. The fuel cladding integrity during dry storage depends on the amount of oxidation, irradiation hardening and hydrogen-uptake during in-reactor operation. In this paper, the effect of hydrogen on the creep behavior of Zircaloy-4 cladding material was investigated at different temperatures. Depending on temperature, hydrogen can be found in the sample in solid solution and/or hydride. To capture this phenomenon, a numerical mesoscale model of the hydrogenated material has been built using the Finite Element (FE) Method. The numerical setup explicitly describes the hydrides as an inclusion in a hydrogenated Zircaloy-4 matrix. The matrix creep behavior follows a combined Norton-Bailey and Norton creep rules whereas the hydrides are considered to be elastic material. The creep law was defined in FE Code ABAQUS using the user subroutine CREEP. The comparison of predicted creep behavior obtained from numerical modeling showed good agreement with the results reported in literature. The predicted creep behavior shows a significant effect of hydrides morphology. Particularly, our model is able to seize the competition between the creep strain rate enhancement induced by hydrogen in solid solution and its reduction due to precipitated hydrogen.     

Increase the current density and reduce the defects of ZnO by modification of the band gap edges with Cu ions implantation for efficient,flexible dye-sensitized solar cells (FDSSCs)

Flexible dye-sensitized solar cells (FDSSCs) have good potential in future photovoltaic technology. The spin coating method deposited the ZnO films on indium-tin-oxide-coated polyethylene terephthalate (ITO-PET) flexible plastic substrates. These films are implanted with Cu-ions with 1 × 10¹³ ions/cm², 1 × 10¹⁴ ions/cm², and 1 × 10¹⁵ ions/cm². All the films have a hexagonal structure. The film irradiated with 1 × 10¹⁴ ions/cm² showed high crystallinity and crystallite size. Important optical properties like bandgap energy (E_g), band edges, refractive index, extinction coefficient, and dielectric constants are measured by UV–Vis spectroscopy. Bandgap energy decreases, and the refractive index increases at the fluence of Cu ions. The maximum decrease in E_g is observed at the 1 × 10¹⁴ ions/cm² dose. Photoluminescence spectra suggest that defects-related emission peaks are decreased at 1 × 10¹⁴ ions/cm² Cu ions fluency. J-V measurements have significantly improved photovoltaic performance compared to pristine ZnO-based solar cells. The highest efficiency (2.30%) is observed at a 1 × 10¹⁴ ions/cm² dose. The efficiency increase is related to improving the charge transfer ratio and shifting the fermi level toward the conduction band.     

Formation of deformation bands and precipitation of Ni3Al(γ′) phase in NiAl(β)-based single crystals by thermomechanical processing

Microstructure and crystal orientation distribution of two-phase NiAl(β)/Ni₃Al(γ′) alloys obtained by thermomechanical processing were investigated. Cylindrical Ni-36 and 38 at.%Al alloy single crystals with various initial loading axes were hot-compressed at a high strain rate of 1.0 s⁻¹ and subsequently annealed in the (β/γ′) two-phase region. After the hot deformation, relatively uniform subgrain structures were formed in initial 〈111〉_β-oriented crystals, while a number of deformation bands perpendicular to the compressive axis developed in 〈100〉_β-, 〈110〉_β- and 〈123〉_β-oriented crystals. Two types of deformation bands with different crystal orientations were alternately arranged against the compressive axis. After annealing in the (β/γ′) two-phase region, a film-shaped γ′ phase with peculiar variants of the Kurdjumov–Sachs orientation relationship preferentially precipitated along the boundary between the deformation bands, resulting in the formation of a (β/γ′) two-phase lamellar structure. Formation process of the deformation bands in β phase and the crystallography of γ′ precipitates along deformation bands were discussed.     

Crack initiation and propagation in braided SiC/SiC composite tubes: Effect of braiding angle

Crack initiation and propagation in three braided SiC/SiC composite tubes with different braiding angles are investigated by in situ tensile tests with synchrotron micro-computed tomography. Crack networks are precisely detected after an image subtraction procedure based on Digital Volume Correlation. FFT based simulations are performed on the full-resolution 3D images to assess elastic stress/strain fields. Quantitative measurements of the crack geometries are performed using a novel method based on grey levels. The results show that braiding angle has no obvious effect on the location of crack onsets (initiation always occurs at tow interfaces), whereas it significantly affects the paths of crack propagation. This work provides an explicit demonstration of the crack propagation scenarios with respect to the mesoscopic fibre architectures.     

Micromechanical properties and microstructural evolution of Amosic-3 SiC/SiC composites irradiated by silicon ions

In this work, Amosic-3 SiC/SiC composites were irradiated to 10 dpa and 115 dpa with 300 keV Si ions at 300 °C. To evaluate its irradiation behaviour and investigate the underlying mechanism, nanoindentation, AFM, Raman and electron microscopy were utilized. Nanoindentation showed that although micromechanical properties declined after irradiation, hardness and Young’s modulus were maintained better under 115 dpa. AFM manifested differential swelling among PyC interface, fiber and matrix and SEM showed irradiation-induced partial interface debonding, which are both more obvious under 115 dpa. TEM revealed the generation and proliferation of amorphous regions, which is according with the decline and broadening of peaks in Raman spectra. The material was almost completely amorphous after irradiated to 10 dpa while recrystallization occurred under 115 dpa. All results mentioned above contribute to the decline of hardness and Young’s modulus and may explain why the micromechanical degradation was more significant under 10 dpa.     

Effect of dissolved oxygen on corrosion behavior of Zr–0.85Sn–0.16Nb–0.37Fe–0.18Cr alloy in 500 °C and 10.3 MPa super-heated steam

To better understand the role of dissolved oxygen (DO) in affecting corrosion behavior of zirconium alloys, the Zr–0.85Sn–0.16Nb–0.37Fe–0.18Cr (wt.%) alloy was corroded in super-heated steam at 500 °C and 10.3 MPa under 1×10⁻⁶ DO and deaeration conditions. The microstructure of the alloy and oxide films was investigated by SEM, TEM, EDS and EBSD. Results show that the corrosion is aggravated under 1×10⁻⁶ DO. Compared with the deaeration condition, the oxide film is looser, and has more micro-cracks and more uneven inner surface under DO condition. For the oxide film forming under deaeration condition, the selected area diffraction (SAED) spots of planes (002)_m, and (101)_t are strong, while those of the (001)_m and are weak. However, for the oxide film forming under DO condition, the SAED spots of planes (111)_m, (200)_m and (101)_t are strong, while those of the (100)_m and (110)_m are weak. The higher DO content in super-heated steam accelerates the growth of oxide films, thus decreasing the corrosion resistance of zirconium alloys.