查看更多>>摘要：The AGR-2 experiment produced normal operation and accident condition fuel performance data for tri-structural isotropic (TRISO) particles with UCO and UO2 kernels. Data for compacts with no failed particles and for compacts with one or more failed particles are available. To model the fission product diffusion and release from these compacts, it is important to consider the computational mesh as well as the heat conduction and mass diffusion properties of the materials in a TRISO particle. Code and solution verification studies with the Bison fuel performance code were performed to show that the code is computing correct solutions. Bison comparisons to post-irradiation examination data and PARFUME predictions were made for several sets of compacts. These comparisons considered silver, cesium, strontium, and krypton with and without failed particles. Bison predictions closely match those of PARFUME, while both codes generally overpredict post-irradiation examination data.
查看更多>>摘要：For the online detection of failed fuel pin in Prototype Fast Breeder Reactor (PFBR), Failed Fuel Localization Module (FFLM) facility is designed to probe the sodium (Na) coolant. Fission Gas Sparging Module (FGSM) is retrofitted with FFLM to localize failed fuel subassembly during the dry rupture of the fuel pin. FGSM is used to purge gaseous fission products (krypton (Kr) and xenon (Xe)) from Na, using argon (Ar). In this work, the efficiency of separating inactive Kr and Xe noble gases with Ar purge out of liquid Na, by their collection onto activated charcoal at cryogenic temperatures and the consequent release at high temperatures into the gas samplers was studied using gas chromatography (GC). Studies of the recovery of Xe/Kr separately with and without Na matrix in the FGSM under both static and dynamic conditions were undertaken by sequentially collecting these probe gases along with excess of Ar in different gas samplers which were then estimated using GC. Density Functional Theory (DFT) computations were performed on model Na clusters surrounding Kr/Xe atoms and also on pyrene molecule (a prototype for simulating the spaces within charcoal), trapping Kr and Xe atoms. Experimental observations showed a good correlation with the results obtained from Quantum Theory of Atoms In Molecules (QTAIM), Natural Bond Orbital (NBO), Energy Decomposition (ED), Non-Covalent Interaction (NCI) and Electrostatic Potential (ESP) mapping analyses. Calculated thermochemical parameters affirm the binding of Xe with Na and charcoal to be marginally stronger than that of Kr, consistent with the experimental observations and speculations based on their polarizabilities.
查看更多>>摘要：Cr-coated Zr alloy claddings, prepared via physical vapor deposition (PVD), were used to study the damage evolution under a series of high-temperature steam oxidation conditions. Through-thickness cracks were initially produced within the Cr coat by internal pressure creep test. The Cr-coated samples with cracks were then oxidized at temperatures from 800 °C to 1200 °C in water steam environment. Microstructures of the samples before and after oxidation were characterized in comparison by scanning electronic microscopy, transmission electronic microscopy and energy dispersion spectrometry. The results showed that a large proportion of cracks would be self-healed when the temperature increased to 1000 °C. At the places where the cracks have survived, the corresponding Zr substrate regions were oxidized to form semi-spherical or fan-shaped ZrO2. However, the maximum depth of ZrO2 under the unhealed cracks was smaller than that of the uncoated claddings at the same oxidation conditions.
V Kaziev A.M Kharkov M.S Efimov V.M Gasparyan Y....
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查看更多>>摘要：In order to simulate ITER transient events with surface heat load parameters relevant to edge-localized-mode (ELM) impacts, tungsten samples were exposed to pulsed heat loads using pure deuterium (D) and with 10% helium (He) seeding plasmas in quasi-stationary high-current plasma gun QSPA-T. The pulse duration was 1 ms that is relevant to ELMs and number of pulses was varied from one to thirty. The power load was 0.7 MJ/m2 that is below the tungsten melting temperature (Tm). Two tungsten samples were used, namely, polycrystalline tungsten without (W) and with pre-existing He-induced W ‘fuzz’ (Wf). Similar to the steady state plasma, the presence of He in tungsten leads to a reduction of the D retention during transient events at temperature below Tm. We explained it as interruption of the D diffusion towards to the bulk of tungsten by (i) the strain field induced by He bubbles and (ii) the formation of interconnected He bubbles at high temperature which leads to an open porosity for accelerated D desorption, thus, decreasing the D influx into the tungsten bulk. But as the He retention in Wf decreases below 1019 He/m2, the effect of He on the D retention after the plasma gun irradiation disappears: the D retention in W and Wf is the same after 30 pulses of the exposure to pure D plasma. In both cases of pure D and He seeded D plasma gun exposures, the D retention is higher compared to the steady state plasma exposure at sample temperature above 600 K.
查看更多>>摘要：The creep behaviour of two ex-service type 316H austenitic stainless steel casts with different Mn contents and austenite grain size, that were pre-carburized for either 8000 h at 550 °C or 3000 h at 600 °C in simulated CO2-rich gas environment of UK Advanced Gas-cooled Reactors, was evaluated by uniaxial creep testing at 550 °C in air. The low Mn (0.98 wt.%) steel grade with an average austenite grain size of 142 ± 110 μm presents a higher creep deformation rate and creep ductility compared to the high Mn (1.52 wt.%) steel cast with an austenite grain size of 81 ± 67 μm. Below an applied stress of 318 MPa, the presence of the sub-surface carburized layer reduces the minimum creep rate, likely due to the significantly modified material properties of the carburized layer and the presence of local compressive stresses. The stress exponent determined for the high Mn steel carburized at 600 °C (n = 9.6), and its reference non-carburized microstructure (n= 9.8), identifies the dominant creep mechanism to be dislocation climb & glide. However, crack evolution through M23C6-decorated grain boundaries within the carburized layer was observed in all the tested material's conditions at creep strains of 0.50%. The average crack length increases with creep strain and attains values close to the carburized layer thickness at creep strains of ε ≥ 1.00%. The prevalence and size of cracking increases with the local hardness carburized layer depth. At applied stresses σ ≥ 318 MPa, cracking on-loading prior to forward creep already occurs in the carburized layer, leading to a sharp increase in minimum creep rates of carburized specimens. These results demonstrate the impact a relatively thin layer of modified material can have on the materials creep performance; emphasising the requirement to consider the effects of the service environment in structural assessment procedures, particularly for high temperature applications including Generation IV and advanced modular reactor designs.
查看更多>>摘要：Excess amounts of dissolution agents, CdCl2 and ZrCl4, are required to dissolve transuranium (TRU: Pu and minor actinides) nitrides into LiCl-KCl melts at the chemical dissolution step, which is the first step in the reprocessing of used nitride fuels. We propose an electrochemical process where the remaining Zr and Cd are recovered from the melts to be recycled as dissolution agents for the chemical dissolution step, leaving TRU in the melts. Since the initial concentration ratio of CdCl2/ZrCl4 remaining in the melts would depend on the condition of the chemical dissolution step and would vary during the proposed electrochemical recovery process, electrochemical behaviors of Zr and Cd were investigated in LiCl-KCl melts with various concentration ratios of CdCl2/ZrCl4 at 723 K to confirm the basic feasibility of the proposed process. Potentiostatic electrolysis was performed using a liquid Cd cathode at -1.05 V (vs. Ag/AgCl), which was a more positive potential than the redox potentials of TRU on the liquid Cd electrode. The obtained results showed that the current efficiency for recovering Zr and Cd from the melts was as high as 100% regardless of the CdCl2/ZrCl4 concentration ratio in the melts.
查看更多>>摘要：Uranium silicide compounds have attracted intensive attention as candidate alternative fuels in commercial light water reactors (LWRs). In this work, the electronic, thermal, mechanical and elastic properties of U3Si5 are comprehensively investigated based on first-principles density functional calculations and semi-classical Boltzmann transport theory. U3Si5 is determined to be a brittle and magnetic metal, and thermal conductivity is dominated by its electronic contribution at high temperature. The ratio between the bulk and shear moduli is 1.205. In addition, the elastic ideal strength is strongly anisotropic, with the minimum value only 6.831 GPa at a uniaxial tensile strain of 0.07. This low strength is mainly caused by an emerged structural transition forming silicon-silicon bonds to absorb strain energy. Moreover, the influences of aluminum incorporation on the structural and elastic properties, and thermal conductivities of U3Si5 are further studied. The aluminum atom prefers to replace the silicon atom at the vertex shared by the silicon triangles and pentagons. The incorporated atom impedes the structural transition, and enhances the toughness of U3Si5. The results from this work may provide useful clue for the improvement in the application of U3Si5.
查看更多>>摘要：The mechanical behavior of a 15 μm-thick chromium coating deposited on a zirconium alloy substrate using a particular physical vapor deposition process is studied at room temperature using several experimental techniques at different scales: biaxial tests (internal pressure + axial tension) with several stress biaxiality ratios on outer-coated tubes; in situ tensile tests in a scanning electron microscope (SEM) on coated sheet samples. The cracking and plasticity of the coating are studied using acoustic emission, digital image correlation and SEM observations. The results show that the first channeling cracks in the coating initiate at 0.3-0.4% macroscopic strain, when the substrate starts to yield. Under further loading, the crack density increases first rapidly then more slowly, before reaching saturation. Plastic strain of the non-cracked coating regions is observed, in addition to the increase of crack opening. No interface decohesion of the coating is observed. The cracks, both transgranular and intergranular, do not penetrate significantly into the substrate.
查看更多>>摘要：1Molecular dynamics simulations were performed to investigate the nucleation and growth of helium bubble on W/Ta semi-coherent interface. It is found that misfit dislocation has a significant impact on the nucleation and growth of helium bubble. He bubble energetically prefers to nucleate at the intersections of the misfit dislocations or on some misfit dislocations. During the bubble growing process, metal interstitial atoms pushed out by the bubble are directly absorbed into nearby misfit dislocations, leading them to climb towards the Ta side; in turn, the climbed misfit dislocations induce He bubble moving away from the bimetal interface and into Ta side. Finally, the misfit dislocation effect on the bubble growth was further discussed in terms of wetting theory.
查看更多>>摘要：We present an engineering-scale model for the migration of porosity in a fuel pellet experiencing a temperature gradient. The system of coupled pore advection and heat diffusion equations governing the problem is solved by a fixed-point iteration technique. The coupling between porosity and temperature fields is considered via the dependency of pore advection velocity on the local temperature and temperature gradient, and via the dependency of fuel thermal conductivity and of the volumetric power source on the local porosity. We employ the finite element method to discretize the resulting equations. As pure advection solutions obtained by this method are well-known to present spurious spatial oscillations, we introduce stabilization techniques in the pore advection equation. The proposed model is first tested against a benchmark problem representative for the conditions of an uranium-plutonium oxide fuel pellet irradiated in a sodium fast reactor. The results are compared to the those obtained by a model implemented in the BISON fuel performance code. The analysis shows how the results of the newly developed model are in line with those obtained by the reference model, and underlines a superior stability of the solution. The model is then applied to analyze the contribution of as-fabricated and crack-induced porosities in determining the fuel restructuring and in particular the central hole formation. A comparison to experimental data shows the impact of considering crack-induced porosity to predict the extent of the central void.
NSTL
Elsevier