Annals of Nuclear Energy最新文献

With increased industry interest in extending reactor operating cycles, the neams! (neams!) program has been investigating the behavior of high-burnup fuel during design basis accidents such as the lbloca! (lbloca!) with consideration for risk of ffrd! (ffrd!). As part of that activity, the neams! subchannel th! (th!) code, CTF, is being used for modeling of lbloca! and to determine the impact of subchannel resolution on results. Although CTF includes a wide range of models for lbloca! conditions, the code has not been used for this application while maintained at ornl! (ornl!) until now. Therefore, in this work, a preliminary assessment of several of these models was performed using openly available reflood experimental data from the feba! (feba!) tests. One coarse mesh and one fine mesh model were set up in CTF for high and low flooding rate tests performed in the unblocked feba! facility. A coarse TRACE model was set up to be as consistent as possible with the coarse CTF model to allow for code-to-code benchmarking. The assessment shows a tendency of the codes to over-predict pct! (pct!) near the top of the bundle and to quench early. Advanced spacer grid models were shown to improve upper bundle predictions in CTF. The resolved CTF model over-predicted pct! by a larger degree in the center channels in the low-flooding rate test, and it is believed that the radiative heat transfer model, which was not used in this study, may be needed to correct this over-prediction. Finally, this work demonstrates the importance of the droplet model in determining quench time and vapor temperature and pct! prediction, which necessitates a more in-depth validation of these models in the future.

Numerical analyses were conducted to simulate the flow boiling phenomenon using different boiling models under natural circulation conditions. From the analyzed results, bubble behaviors were investigated at the onset of nucleate boiling (ONB) and the onset of flow instability (OFI). At the ONB, the predictions obtained for the bubble diameter, nucleation site density, and void fraction were compared with the experimental data. At the OFI, the bubble diameter, nucleation site density, void fraction, and bubble movement with respect to time were investigated. Among 4 cases with different combinations of boiling models, Case 1 was selected because the wall temperature, bubble diameter, nucleation site density, and void fraction were well predicted considering the agreement between the experimental and computational fluid dynamics results. When flow instability started as the heat flux increased, bubble behavior was nonuniform although heat flux was uniformly generated on the heated surface.

The LFR is a candidate for the Generation-IV nuclear systems, where the process of MFCI differs from that occurred in LWRs and SFRs. In the absence of experimental study and widely applied theoretical models for LFRs, experiments on the interaction between molten SS and liquid LBE are conducted in this study under eight conditions. The morphological characteristics and fragment sizes of the products are analyzed based on the hydrodynamic effect parameter (We) and thermal effect parameter (T_ic). Simplified thermal fragmentation models are established, where the innermost layer of the solidified shell is subjected to the maximum tangential compressive stress, while the outermost layer is subjected to the maximum tangential tensile stress. As the shell thickness increases, the total tangential stress of the outermost layer decreases. The fragmentation will occur when the maximum tangential stress on the shell exceeds the shell tensile strength.

This paper focuses on the application of the Backward Differential Formula (BDF) and Anderson’s method for neutron diffusion transient simulations. The B-spline finite element method is used for spatial discretization of continuous equations into the system of ODEs. BDF with adaptive step size and approximation order is used for integration of the ODEs over time. In-step multigroup equation is solved using the block Gauss–Seidel method, where the inner equation is solved using the ILU(0)-preconditioned Conjugate Gradient method. Anderson’s method is employed first to solve the in-step non-linear equation that couples the neutron and temperature models, and second, to accelerate the convergence of the block Gauss–Seidel algorithm. The performance of the time integration scheme and the in-step equation solver are verified on the point kinetics equation and two-dimensional benchmarks.

Due to the size limitation, the heat transfer characteristics of subcooled flow boiling in the narrow rectangular channel are different from the conventional channels. Surface roughness directly affects bubble formation and detachment in subcooled boiling. This study presents a visualization study on the effect of surface roughness on the heat transfer characteristics and the onset of nucleate boiling (ONB) in narrow rectangular channels, including roughness of 0.34 μm, 1.2 μm, and 2.5 μm. The results indicate that surface roughness can enhance the heat transfer between the fluid and the wall and reduce wall temperature. The heat transfer coefficient in the subcooled flow boiling increases nonlinearly with surface roughness. Large surface roughness can shift the axial position of the ONB forward and reduce the wall heat flux required for subcooled flow boiling. An empirical correlation for predicting the subcooled flow boiling is modified based on Hsu’s nucleation criterion and the experimental data.

In the present work, a newly produced PbO-BaO-B₂O₃ glass system’s mechanical, physical, and radiation absorption capabilities were studied to determine the effectivity of B₂O₃ substitution by ZnO. The melt-quench process produced the glasses utilized in the present investigation. The melting point used was 1000 °C, and the temperature at which they were annealed was 400 °C. The experimental measurement of the density for manufactured glass samples was conducted using Archimedes’ theory. It was observed that all density values of the fabricated glasses were raised when the concentration of ZnO was increased from 0 to 20 mol.%. Based on the model proposed by Makishima and Mackenzie from Young, bulk, shear, and longitudinal moduli, it was observed that there was a decrease as the concentration of ZnO was increased in the manufactured glasses. Microhardness was found to be reduced from 4.692 GPa to 4.218 GPa, while the Poisson ratio was found to be decreased from 0.234 to 0.229 when the percentage of ZnO was raised from 0 to 20 mol.%. In contrast, the assessment of radiation shielding qualities through the utilization of Monte Carlo software simulation demonstrates an augmentation in the radiation absorption capability of the manufactured glass samples due to the exchange between B₂O₃ and ZnO compounds. We used the MCNP5 code to study the radiation shielding properties in a wide energy range of 0.03–2.605 MeV. The linear attenuation coefficient LAC of the produced glass samples increased from 0.315 cm⁻¹ to 0.369 cm⁻¹ when the ZnO concentrations were enriched from 0 to 20 mol.%, respectively.

Helically coiled tube under ocean conditions will subject to serious two-phase flow instability. This study experimentally investigated two-phase flow instabilities in a helically coiled tube under static and rolling conditions. Under static condition, Density Wave Oscillation (DWO), Pressure Drop Oscillation (PDO), and Thermal Oscillation (TO) are observed, and the stability map for DWO is established. Under rolling condition, Single-phase flow oscillation, PDO, and DWO are observed, and compared to the phenomena of static condition. It is found that rolling condition can induce flow oscillation, making the DWO and PWO more severe. Through Fast Fourier Transform (FFT) analysis, it is found that impact of rolling conditions on flow instability diminishes as heating power is increased. In addition, the parameter effects of inlet subcooling, volumetric flow rate, system pressure, rolling angle and rolling period on flow stability are investigated.

The borate glass system was prepared using the melt-quenching method. The XRD was used to confirm the amorphous structure of present samples, the FTIR was utilized to observe vibration modes, and the UV–Vis-NIR spectrophotometer was employed to measure transmittance spectra. The radiation shielding properties were examined by FLUKA Monte Carlo simulation, XCOM programs, and experimental methods. The density increased, while the molar volume decreased as the BaO content increased. For the X-ray and gamma-ray radiation, indicate that the addition of BaO instead of B₂O₃ improve the shielding properties, while the Σ is decreased for thermal neutron radiation. According to the results, adding BaO enhanced the X-ray and gamma-ray shielding properties. However, adding BaO led to the reduces its ability of shielding the thermal neutrons of the glass samples. These data are expected to be accommodate to considering for any applications which requires high efficiency of photon or thermal neutrons shielding.

The helical cruciform fuel (HCF) is characterized by self-supporting and enhanced transverse mixing, which may replace the cylindrical fuel in commercial light water reactor (LWR). In the presented work, the experimental study on the flow resistance and phase distribution of a 4 × 4 HCF assembly was carried out. The experimental system of air–water two-phase flow was established, and the wire-mesh sensor (WMS) technology was introduced for the void fraction measurement and flow regime identification. The two-phase hydraulic loss of the HCF assembly was larger than that of the pipe and cylindrical rod bundle. The liquid phase friction multiplier of HCF assembly was decreased by increasing the mass flux. The flow regimes involve the bubble flow, cap bubble flow, cap churn flow and churn flow were found in the HCF assembly. The gas phase was gathering towards the central region of HCF assembly by the directional cross-flow. Besides, the two-phase friction multiplier correlation and drift flux model for the HCF assembly were proposed.