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• The design of the Core Assembly Deformation Test Facility was described in detail. • The conditions of assembly bending and thermal bowing tests were introduced briefly. • The heating and measurement technologies and the layout of sensors were introduced. China Demonstration Fast Reactor (CFR600) is under construction, and the Sub-assembly Deformation Analysis Program (SDAP) developed by China Institute of Atomic Energy is used to optimize the core design and operation management of CFR600. The Core Assembly Deformation Test Facility (CADTF), designed and built by Xi'an Jiaotong University, was selected to carry out a series of assembly bending and thermal bowing tests to provide validation problems for the SDAP. The specimen assembly was specially designed for better non-intrusive optical temperature measurement of the inner wrapper tube. The automatic heating control method and a lot of new measurement technology were applied into the tests to gain abundant and accurate test data. [ABSTRACT FROM AUTHOR]

Highlights • A new method was proposed to simulate thermal deformation of subassembly in SFR. • Assembly deformation analysis code FADAC was developed and applied in the present study. • Free bowing was analyzed under different temperature conditions and displacement field of the subassembly was obtained. • Restrained bowing was analyzed in detail and maximum deflection was calculated. Abstract Due to the special geometry and compact arrangement of subassemblies in the sodium-cooled fast reactor, thermal deformation of the assemblies are easily triggered by uneven temperature distribution in the reactor core, which is negative for reactor safety. Therefore, it is necessary for researchers and engineers to conduct quantitative analysis towards thermal deformation behaviors of subassemblies, and furthermore, give reliable evaluation results on aftermath of the assembly thermal deformation. In the present study, thermal deformation analysis code FADAC, which was developed based on Euler-Bernoulli beam theory, was applied to make numerical investigation for thermal deformation behaviors of a single subassembly in sodium-cooled fast reactor. In order to preliminarily assess the capacity for thermal deformation, different temperature gradient conditions were considered and analyzed in detail for free bowing of the subassembly, furthermore, with the aid of numerical analysis for thermal axial forces and thermal bending moments, axial displacements and deflections were calculated finally. Besides, in order to predict the comprehensive results of the assembly deformation under both thermal load and mechanical load, restrained bowing were also analyzed for different temperature conditions. All of the simulation results were in good accordance with the experimental data. The present numerical research is of great significance to assembly deformation research in the sodium-cooled fast reactor, and will surely lay a solid foundation for deformation analysis towards multi-subassemblies. [ABSTRACT FROM AUTHOR]

• Three-dimensional simulation (3D) of fuel relocation under loss-of-coolant accident is performed by using discrete element method. • The 3D simulation of fuel relocation is firstly validated by the in-pile experiments. • The critical parameters like fuel stack reduction, mass fraction and filling ratio are influenced by the mean diameter of fuel fragments. • The exponentially fitting correlations are proposed for the fuel stack reduction as a function of the relative cladding volume increase. • The exponentially fitting correlations are proposed for the mass fraction and filling ratio as a function of the cladding circumferential strain. This work presents the three-dimensional (3D) simulations of fuel relocation during loss-of-coolant accidents based on the coupled FEM-DEM approach. A simple equivalent approach is employed to generate the fragment geometry with the mean diameter as the fragment size measured in the sieve test. For the first time, the 3D simulation of fuel relocation is validated by the in-pile experiments performed in the FR2 research reactor. The predicted missing fuel length is in good agreement with the experimental data, indicating the viability and effectiveness of the simulation. According to the features of fuel relocation, the parametric study on fragment mean diameter and cladding volume increase is conducted. Based on the quantitative analysis, it is found that the fuel stack reduction exponentially increases with the relative cladding volume increase. Also, the mass fraction and the filling ratio seem to exponentially increase and decrease with cladding circumferential strain, respectively. A series of fitting correlations of fuel stack reduction, mass fraction and filling ratio are proposed for different fragment mean diameters. By implementing the empirical correlation of filling ratio, the capability of the one-dimensional model is improved to gain a close predicted result as 3D simulation. The proposed correlations can support the interpretation of experimental data, and can enhance the evaluation accuracy of fuel performance during loss-of-coolant accidents by the more realistic prediction of the critical parameters influenced by fuel relocation. [ABSTRACT FROM AUTHOR]

• Equilibrium equations and compatibility equations were conducted respectively to consider coupling effects of subassemblies in SFR. • Calculation for row bowing was performed with the aid of FADAC code in the present study. • Row bowing was analyzed in detail under different geometric parameters for wrapper tube, even core baffle was taken into consideration. • Reaction forces and deflection parameters were obtained by calculation, which are meaningful for safety evaluation and core structural design. Subassemblies in sodium-cooled fast reactor are different from pressurized water reactor in both geometry and assembly arrangement. In sodium-cooled fast reactor, assembly thermal deformation and narrow clearance between adjacent assemblies would cause them contact with each other, and reaction force between neighboring pads would occur. Under that circumstance, assembly deformation would be decided by both thermal load and mechanical load, which means significant coupling effect would lead to more complicated deformation behaviors. Therefore, so as to deeply study such thermal–mechanical coupling effect in reactor core, it is meaningful to conduct theoretical analysis and numerical simulation on such behaviors, which is indispensable for reactor safety analysis and structural design. In the present study, equilibrium equations and compatibility equations were conducted respectively for acquiring deformation parameters of assemblies in the row, which were already implemented into FADAC code and can perform calculation for row bowing. Furthermore, reaction forces and assembly deflections were analyzed in detail. Besides, sensitivity analysis were performed for row bowing calculation, in which wrapper tube thickness, distance across flat for wrapper tube, pad clearance and effects of core baffle were all taken into consideration. The present theoretical research for assembly deformation in SFR is essential for reactor safety and structural design, and will lay a solid foundation for assembly deformation analysis in the whole core. [ABSTRACT FROM AUTHOR]

• Behavior of Cr-coated clad under integral LOCA test is simulated in FEA. • Current burst criteria for Zircaloy is ineffective to capture Cr-coated concept. • New overstress and plasticity instability criteria for the Cr coating are proposed. • Coating thickness is found to be numerically insensitive to burst temperature. Chromium (Cr) coated cladding is one of the most promising accident-tolerant fuels for pressurized water reactors. The behavior of Cr-coated cladding under the accident conditions is crucial to quantify its implication on safety, licensing and economics. This work focuses on the modeling of the burst behavior of Cr-coated cladding under Loss of Coolant Accidents (LOCAs). For this purpose, the material properties and behavior models of Zircaloy and chromium have been studied and implemented into the ABAQUS. Then the ABAQUS models are compared against several burst tests done by Korea Atomic Energy Research Institute (KAERI) and Électricité de France (EDF). During the comparison process, different high temperature creep models, zircaloy cladding burst criteria and coating thicknesses are adopted to investigate the thermo-mechanical performance and burst behavior of Cr-coated claddings under LOCA. Based on the comparative computational analysis, 100% and 85% Cr fracture strength and the strain rate of 0.23 /s and 0.07 /s are proposed as a new overstress burst criterion for coated cladding under a heating rate from 5 K/s and 10 K/s. The effect of coating thickness on the proposed criteria and the ballooning behavior of the coated cladding was predicted to be insignificant. The proposed criteria are beneficial for better understanding of the coated clad burst phenomena and the best estimation of coated clad performance under LOCA scenarios. [ABSTRACT FROM AUTHOR]

Under normal operation, oxide nuclear fuel pellets subjected to high thermomechanical loading and irradiation damage can develop complex crack networks, separating the fuel pellet into a pile of fragments. During a Loss of Coolant Accident (LOCA), these pellet fragments, or fine powder especially when originating from the high-burnup fuel pellet periphery, may relocate axially into the ballooned region of the zircaloy cladding. In this work, the axial relocation process of fuel fragments and powder is modeled based on the three-dimensional Discrete Element Method (DEM) in the Abaqus software. A Voronoi tessellation technique is adopted to generate random convex polyhedrons in order to mimic a coarse fragmentation pattern. A parametric study in terms of the mean fragment size from 1.3 mm to 3.0 mm was conducted to investigate its effect on the axial profile of fuel mass fraction and filling ratio after fuel relocation. Then a sensitivity study of the randomness in fragmentation on axial fuel relocation was performed. For high-burnup fuels, in order to characterize the porous High Burnup Structure (HBS), the pellet rim was discretized into separate spherical shape particles. The effect of powder fraction on fuel relocation was demonstrated, and the results indicated that higher powder fraction can significantly increase the fuel mass fraction and filling ratio level in the ballooned region, which showed qualitative agreement with experimental observations. Finally, the verification against a one-dimensional theoretical relocation model was conducted to verify the robustness and high fidelity features of the DEM model in simulating axial fuel relocation under LOCA. The modeling approach serves as a mechanistic framework to support future burnup extensions for the oxide nuclear fuel. [ABSTRACT FROM AUTHOR]

• The assembly compression test was described, and the section stiffness were given. • The assembly bending test was described, and the bending stiffness were given. • Compared and discussed the data of the IAEA benchmark tests and the XJTU tests. China Fast Reactor (CFR) is under construction, and the section stiffness and bending stiffness of CFR assemblies remain unknown and need to be investigated to support the core restraint system design and reactivity safety assessment. In this study, assembly compression tests were performed with three types of test samples. With the compression load varying from 0 to 6 kN, the compressive deformations were measured and the section stiffness were obtained. In assembly bending tests, there were two types of assemblies considering different spike clearances, and the horizontal loads from 400 N to 1900 N were applicable to the upper-load-pad, lower-load-pad and mid-fissile-region level of the assemblies. Assembly deflections were measured and correlations for the load-deflection ratio were proposed. Comparison of theoretical and experimental bending stiffness were carried out, which indicated that the spike clearance has to be taken into consideration in the assembly deformation analysis codes. [ABSTRACT FROM AUTHOR]

• A font-based text watermarking scheme is proposed to achieve robustness to cross-media distortions such as print-camera shooting, screen-camera shooting, and print-scanning. • A glyph centroid modification-based font codebook generation algorithm is proposed to automatically create target-similar fonts. • The proposed method does not require the participation of OCR to identify glyphs, which can improve the extraction accuracy and efficiency. • The proposed method is applicable with various font sizes, languages, and devices. The rapid development of digital devices and the increasing demand for copyright protection and leakage tracing of documents result in new demands for robust text watermarking. It becomes more important for a utility text watermarking scheme to have robustness in cross-media channels since the camera shooting operation to papers or screens has become very convenient. To achieve the corresponding cross-media robustness, this paper proposes a font-based text watermarking scheme, which is applicable to most commonly used languages while the previous works were usually designed for specific languages. To generate fonts with high efficiency, we propose a novel glyph centroid modification-based font generation algorithm, which can automatically create target-similar fonts. And we design an effective watermarking scheme that utilizes the relative centroid position (RCP) of glyphs to represent watermark signals. Compared with existing font-based text watermarking schemes that artificially design fonts, the proposed scheme ensures higher efficiency by generating the font codebook automatically. In addition, the proposed RCP-based watermarking scheme can achieve the robustness against lossy compression and several kinds of cross-media distortions. The watermark message can be extracted without the need to recognize the semantic information of glyphs by optical character recognition (OCR). [ABSTRACT FROM AUTHOR]