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Fuel assemblies have a decisive impact on the performance and safety of nuclear reactors. Helical fuel has huge potential for application in small module reactors (SMRs) due to its advantages in volume power density and safety. Typical helical fuel elements are usually trilobal or cruciform in cross-section. The fuel rods are helically twisted in the axial direction, eliminating the need for spacer grids as the fuel rods are self-supporting. In this paper, a refined subchannel division approach is proposed based on the crossflow mechanism of helical fuel assemblies. Then, a refined helical fuel mixing model framework, including the helical fuel distributed resistance method and directed crossflow method, is developed and implemented in a helical fuel rod bundle to investigate the mixing characteristics. Validation is provided by a 5×5 helical fuel bundle mixing experiment. The refined model predicts about 92.7% of the data with the ±10% error range. Compared with existing helical fuel mixing models, the refined mixing model has higher axial accuracy and radial spatial resolution, and can accurately predict the twist angle-dependent crossflow rate and entry effect. Meanwhile, the refined helical fuel mixing model framework is universal and can be effectively used for the mixing prediction of arbitrary geometric helical fuel after the calibration of coefficients.

The subchannel analysis method is one of the most crucial transient safety analysis methods in the thermal design of nuclear reactors. The nonuniformity of circumferential heat transfer is slight in conventional pressurized water reactor (PWR) cores, but it is significant in advanced reactors with wire-wrapped or helical fuel rods. Predicting circumferentially nonuniform heat transfer behavior can be challenging owing to the complex geometry of helical fuel rods. In this study, a general circumferentially nonuniform heat transfer fuel rod (GCNF) model is developed to predict the fuel central temperature and circumferential heat flux and wall temperature. This model incorporates a refined two-dimensional fuel conduction model and circumferential nonuniform shape factor, addressing the dual factors contributing to the circumferential nonuniformity of helical fuel rods. An empirical correlation for the nonuniform shape factor is developed based on the computational fluid dynamics (CFD) results, and it is implemented to the subchannel code. The newly developed model is applied to a helical fuel annulus and validated by comparing the prediction results with CFD data. The maximum wall temperature predicted by the code is 1.15°C lower than the value calculated through CFD. In terms of the heat flux, the maximum value at the inner corner is 22 kW lower than that obtained from the CFD prediction. The accurate prediction of circumferentially nonuniform heat transfer in helical fuel, concerning the surface heat flux and cladding temperature, addresses existing shortcomings in helical fuel subchannel analysis methods. Additionally, the capability to predict the fuel central temperature is essential for the safety analysis to determine whether fuel rods are melting. The generality of the model framework allows it to be used for the prediction of circumferential nonuniform heat transfer behavior in other types of fuel assemblies.

The Seebeck effect encounters a few fundamental constraints hindering its thermoelectric (TE) conversion efficiency. Most notably, there are the charge compensation of electrons and holes that diminishes this effect, and the Wiedemann-Franz (WF) law that makes independent optimization of the corresponding electrical and thermal conductivities impossible. Here, we demonstrate that in the topological Dirac semimetal Cd 3 As 2 the Nernst effect, i.e., the transverse counterpart of the Seebeck effect, can generate a large TE figure of merit z N T . At room temperature, z N T ≈ 0.5 in a small field of 2 T and it significantly surmounts its longitudinal counterpart for any field. A large Nernst effect is genetically expected in topological semimetals, benefiting from both the bipolar transport of compensated electrons and holes and their high mobilities. In this case, heat and charge transport are orthogonal, i.e., not intertwined by the WF law anymore. More importantly, further optimization of z N T by tuning the Fermi level to the Dirac node can be anticipated due to not only the enhanced bipolar transport, but also the anomalous Nernst effect arising from a pronounced Berry curvature. A combination of the topologically trivial and nontrivial advantages promises to open a new avenue towards high-efficient transverse thermoelectricity.

Hole-transport-layer (HTL)-free, carbon-based all-inorganic perovskite solar cells (PSCs) are attracting a great interest owing to a low cost and an advanced stability in ambient environment. However, the photoelectric conversion efficiency (PCE) for this kind of PSCs was far lower than expected. Interface engineering is a promising method to enhance PSCs efficiency through improving the interface charge transfer. In our work, we introduce a simple, clean interfacial engineering method of deionized water (DI) spin-coating to treat the F-doped SnO 2 (FTO). And then ZnO was spin-coated on the treated FTO. A compact and highly uniform ZnO film was obtained. Excess CsBr was added into CsPbI 3 precursor solution to obtain stable black phase CsPbI 3 at a low temperature (120 °C). HTL-free, carbon-based all-inorganic CsPbI 3− x Br x ( x  < 1) perovskite solar cells are fabricated with the structure of FTO/DI/ZnO/CsPbI 3− x Br x ( x  < 1)/C. After DI treatment, the defect density of device is greatly decreased so that carriers transport at the interface is accelerated and the charge recombination is effectively suppressed. The champion PCE has been improved from 10.95 to 12.39%, obtaining an improved PCE about 13%, which is the highest PCE for HTL-free, carbon-based all-inorganic PSCs until now.

Background Many studies have shown that distal femoral sagittal morphological characteristics have a clear relationship with knee joint kinematics. The aim of this study was to determine the relationship between distal femoral sagittal morphological characteristics and noncontact anterior cruciate ligament (ACL) injury. Methods A retrospective case-control study of 148 patients was conducted. Two age- and sex-matched cohorts (each n  = 74) were analysed: a noncontact ACL injury group and a control group. Several characteristics were compared between the two groups, including the lateral femoral posterior radius (LFPR), medial femoral posterior radius (MFPR), lateral height of the distal femur (LH), medial height of the distal femur (MH), lateral femoral anteroposterior diameter (LFAP), medial femoral anteroposterior diameter (MFAP), lateral femoral posterior radius ratio (LFPRR), and medial femoral posterior radius ratio (MFPRR). Receiver operating characteristic (ROC) analysis was used to evaluate the significance of the LFPRR and MFPRR in predicting ACL injury. Results Compared with patients in the control group, patients in the ACL injury group had an increased LFPR, MFPR, MFAP, LFPRR, and MFPRR. ROC analysis revealed that an increased LFPRR above 31.7% was associated with noncontact ACL injury, with a sensitivity of 78.4% and a specificity of 58.1%; additionally. an increased MFPRR above 33.4% was associated with noncontact ACL injury, with a sensitivity of 58.1% and a specificity of 70.3%. Conclusion This study showed that increased LFPRR and increased MFPRR are risk factors for developing noncontact ACL injury. These data could thus help identify individuals susceptible to ACL injuries.

By performing experiment and model studies on a triangular-lattice dipolar magnet KBaGd(BO\\(_3\\))\\(_2\\) (KBGB), we find the highly frustrated magnet with a planar anisotropy hosts a strongly fluctuating dipolar spin liquid (DSL), which originates from the intriguing interplay between dipolar and Heisenberg interactions. The DSL constitutes an extended regime in the field-temperature phase diagram, which gets lowered in temperature as field increases and eventually ends with an unconventional quantum critical point (QCP) at \\(B_c 0.75\\)~T. Based on dipolar Heisenberg model calculations, we identify the DSL as a Berezinskii-Kosterlitz-Thouless (BKT) phase with emergent U(1) symmetry. Due to the tremendous entropy accumulation that can be related to the strong BKT and quantum fluctuations, unprecedented magnetic cooling effects are observed in the DSL regime and particularly near the QCP, making KBGB a superior dipolar coolant to commercial Gd-based refrigerants. We establish the phase diagram for triangular-lattice dipolar quantum magnets where emergent symmetry plays an essential role, and provide a basis and opens an avenue for their applications in sub-Kelvin refrigeration.