查看更多>>摘要：The kinetics of uptake and desorption impact the performance of graphite as a vector for tritium in high-temperature fission reactors and in the blanket of fusion reactors. Graphite components in these reactors are exposed to temperatures > 500 °C and H2 partial pressures of few Pa and desorption temperatures are limited to < 1600 °C; limited data is available at these conditions. We review the mechanisms for uptake in, transport and desorption of hydrogen from graphite at high temperature, compiling data on uptake rates, diffusion coefficients and activation energies and providing a discussion of the impact of irradiation, pre-oxidation and isotope. At FHR conditions, trapping impacts uptake rates, leading to a reduction in apparent diffusivity by 35 to 80% compared to higher partial-pressure uptake. Timelines for desorption are not clearly defined; extrapolating from available data, at 1150 °C desorbing 80% of tritium uptaken at FHR conditions may take from 100 to 10,000 h.
查看更多>>摘要：Uranium carbides are receiving renewed interest as a preferred nuclear fuel composition for advanced reactors due to their numerous favorable properties. Like many other refractory and transition metal carbides these compounds exist in both hypo- and hyper-stoichiometric compositions which results in significant variations in physical, thermal, and mechanical properties. This manuscript surveys both historic and recent literature to compile important properties data mainly as a function of temperature and carbon content to support fuel performance modeling. Expressions and fits for such properties are also suggested when allowed by complete data sets. The manuscript also attempts to highlight gaps and discrepancies in the reported data to assist the nuclear fuels community identify key areas that may require further attention in terms of future research and development.
查看更多>>摘要：The authors regret to inform that one of our co-authors, Kenneth C. Littrell, was originally omitted from the author list in our manuscript. The authors would also like to correct a typographical error for the magnetic field strength used for the magnetic SANS measurements, as the value should be 2 T. Finally, the authors regret that an additional acknowledgment was originally omitted from the original release: A portion of this research used resources at the High Flux Isotope Reactor, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. The authors would like to apologize for the inconvenience caused.
查看更多>>摘要：? 2021U3Si2 is of interest to the nuclear industry as a candidate fuel material due to its high uranium density and high thermal conductivity. However, it has been observed to react with hydrogen, resulting in material decrepitation. As a result, it is important to understand the thermodynamics of the U3Si2-H system. In this study, the thermodynamics of the hydrogen absorption reaction of U3Si2 were determined experimentally using Sievert's gas absorption and related to crystallographic evolution with hydrogen content using X-ray diffraction. Experimentally-determined thermodynamic parameters were compared with results from density functional theory modeling. Results from this study were also compared with those determined in previous work. Sievert's gas absorption results were used to develop the pressure-composition-temperature (PCT) curves of the U3Si2-H system. It was found that the hydride phase exhibited a maximum stoichiometry between U3Si2H1.8 and U3Si2H2. The two-phase region for hydride formation from U3Si2 exhibited a miscibility gap with a critical temperature between 623 and 673 K, as calculated from the PCT curves. Analysis of the PCT curves also showed that both the enthalpy and entropy of the hydrogen absorption reaction increased with hydrogen content but were lower than the values for uranium trihydride formation from uranium metal. The enthalpy of reaction for hydrogen absorption was calculated to range between -86.9 and -94.8 kJ mol?1, while the entropy of reaction was calculated to range between 101.9 and 138.8 J mol?1 K?1. DFT modeling of the thermoydnamic stability of the U3Si2 hydride phases yielded a decomposition temperature of U3Si2H2 of approximately 600 K, which was consistent with the experimental results. Similarly, the DFT-calculated enthalpy and entropy of reaction to form U3Si2H1.5 were determined to be -106.5kJ mol?1 and 121.8J mol?1 K?1, respectively, which were both in close agreement with the experimentally-determined values.
查看更多>>摘要：In this study, the compact and uniform CrSi (Cr0.92Si0.08, Cr0.85Si0.15, Cr0.65Si0.35) coatings have been deposited on zircaloy-4 substrates by magnetron sputtering technique, and their oxidation performances in steam environment have been investigated at 1200°C for 60 min. Microstructures and phase compositions of coatings before and after oxidation indicate that CrSi coatings exhibit protective behavior. The dense Cr2O3 oxide layer on CrSi coatings can significantly improve the oxidation resistance, and their weight gains are reduced. The Cr0.92Si0.08 coating shows the optimum performance due to the integrality and protectiveness of the Cr2O3 oxide layer.
查看更多>>摘要：A 2D axisymmetric SiC cladding mechanical model with anisotropic material properties based on finite difference method was developed. The developed model was used to analyze the behavior of SiC clad fuel (double-layer and full SiCf/SiC composites structure) in steady-state and large break loss of coolant accidents (LBLOCA) by coupling with the thermal-hydraulics simulation code MARS-KS (Multi-dimensional Analysis of Reactor Safety-Korean Standard). The multi-axial pseudo-ductile deformation model considering the characteristics of SiCf/SiC composites was employed, and the Weibull statistical failure model was applied to assess the failure probability of the cladding. Using anisotropic elastic properties, stronger tensile stress was induced in the outer monolith layer than in the isotropic case, which greatly increased the failure probability. In steady-state operation, this study shows that the failure probability of a double-layer SiC cladding is sensitive to the rod internal pressure. In-line with other studies, it was also found that the irradiation induced swelling accumulated in the refueling stage is a challenge to the structural integrity of the SiC cladding concept. The LBLOCA analysis demonstrates that the SiCf/SiC composite layer can maintain the coolable geometry of the fuel rod for both duplex and full composite cladding. Hermeticity is shown to depend on the arrestment of matrix cracks developed by pseudo-ductile deformation. Experimental support and validation on matrix crack propagation, pseudo-ductile behavior of SiCf/SiC composite under multiaxial loading, and rod-scale thermal shock with reflood quenching are necessary to further improve the model.
查看更多>>摘要：The Hanford Waste Treatment and Immobilization Plant will vitrify radioactive waste into borosilicate glass. The high-level waste (HLW) glass formulations are constrained by processing and property requirements, including restrictions aimed at avoiding detrimental impacts of spinel crystallization in the melter. To understand the impact of glass chemistry on crystallization, two HLW glasses precipitating small (～5 μm) spinel crystals were individually mixed and melted with a glass that precipitated large (～45 μm) spinel crystals in ratios of 25, 50, and 75 wt%. The size of spinel crystals in the mixed glasses varied from 5 to 20 μm. Small crystal size was attributed to: (1) high concentrations of nuclei due to the presence of ruthenium oxide and (2) chromium oxide aiding high rates of nucleation. Results from this study indicate that the spinel crystal size can be controlled using chromium oxide and/or noble metal concentrations in the melt, even in complex mixtures like HLW glasses. Smaller crystals tend to settle more slowly than larger crystals, therefore smaller crystals would be more acceptable in the melter without a risk of failure. Allowing higher concentrations of spinel-forming waste components in the waste glass enables glass compositions with higher waste loading, thus increasing plant operational flexibility. An additional benefit to the presence of chromium oxide in the glass composition is the potential for the oxide to protect melter walls against corrosion.
查看更多>>摘要：In this work, we demonstrate the applicability of sub-miniaturized three-point bending (3PB) testing for the extraction of tensile plastic properties of metallic materials, such as yield stress and work hardening rate. The approach is developed and validated on the example of tungsten. For this, dedicated finite element method (FEM) simulations are performed to reveal the correlation between the flexural stress-strain response in 3PB tests and yield stress in tensile tests. Furthermore, a dedicated inverse FEM procedure utilizing rate-sensitive isotropic physical model is developed to extract both yield stress and work hardening rate from the available set of bending tests. Both FEM-based approaches are first benchmarked on unirradiated materials and then validated using neutron-irradiated tungsten grades. The accuracy of the tensile properties extracted using both methods is discussed along with the estimation of a number of 3PB tests required to reach a target precision. The applicability of 3PB geometry for the extraction of tensile properties from unirradiated bending tests below ductile-to-brittle transition temperature (DBTT) is also addressed.
查看更多>>摘要：In this study, W-(Y0.9La0.1)2O3 composite powders are fabricated by means of a combination of wet chemical method and spark plasma sintering. We systematically study the sintering and densification behavior of W-(Y0.9La0.1)2O3 composite powders at different temperatures and pressures. The results indicate that ultrafine tungsten-based composites with a dispersed distribution of (Y0.9La0.1)2O3 particles can be achieved under optimized temperature and pressure conditions. The optimized pressure and sintering temperature for W-(Y0.9 La0.1)2O3 composites are identified to be 75 MPa and 1600 °C, respectively. In addition, the surface damage behavior of W-(Y0.9La0.1)2O3 composites induced by the laser thermal shock and helium ion irradiation are also investigated. It is shown that the presence of holes greatly enlarges the helium retention during helium ion irradiation and promotes the melting caused by local overheating during laser thermal shock. We find that the fine-dispersed distribution of (Y0.9La0.1)2O3 particles in the tungsten-based composites can effectively improve the resistance of helium ion irradiation and laser thermal shock. We hope that these findings could provide some guidance and reference for the fabrication of large-sized tungsten-based materials in fusion engineering.
查看更多>>摘要：Reduced Activation Ferritic/Martensitic (RAFM) steel is a candidate blanket material for a fusion reactor, which should have outstanding performance under extreme environments containing complex thermal and stress damage during operation. To date, the properties under a single-axial loading type of tensile, creep and fatigue have been extensively reported, while the multi-axial loadings were rarely studied. Here, the multi-axial fatigue behaviors of a RAFM steel were investigated in an axial-torsional cyclic tester with controlled strain and different loading paths. The results show that the fatigue behavior of the RAFM is strongly determined by the shear-stress condition, where the lifetime under the pure torsional loading is only 16% of the uniaxial cyclic loading one. The fatigue life of the specimens under multi-axial loadings with a phase angle of 0° or 180° are comparable to that of uniaxial tension-compression one. However, it was decreased by ～28% as the loading angle changed to 90° with a circular path. Besides, we found the fatigue softening under the proportional multi-axial loading while additional hardening in the non-proportionally multi-axial cyclic loading related to the dislocation activities during loadings. Under the proportional-multiaxial loading and uniaxial tension-compression loading and torsion loading, the high density of dislocation was rearranged and annihilated by the cyclic shear stress, while the tempered martensite lath structure was mainly retained. However, under the non-proportional multi-axial loading, dislocations transform the lath structure into a finer cell structure, improving the resistance upon fatigue deformation.
NSTL
Elsevier