Clinical data including reoperation rates are comparable for lumbar patients after decompression-alone or decompression-with-fusion surgeries. However, there could exist different mechanisms causing complications after the two surgeries. We discussed research and technology development perspectives for improvement of the surgeries using published clinical outcome data.

The core inlet flow distribution in the APR1000 reactor is critical for ensuring the reactors safety and efficient operation by maintaining uniform coolant flow across fuel assemblies. Previous studies, though insightful, faced challenges in fully replicating reactor-scale flow conditions due to technical and economic constraints associated with scaled-down experimental models and the limited numerical validation methodologies. This study addresses these limitations by developing and validating a robust computational fluid dynamics (CFD) methodology to accurately analyze the core inlet flow distribution. A 1/5 scaled-down experimental model adhering to similarity laws was employed for validation. CFD analyses using ANSYS Fluent and CFX, combined with turbulence model evaluations and grid sensitivity studies, demonstrated that the SST and RNG k-ε turbulence models provided the most accurate predictions, with a high correlation to previous experimental data. Full-scale simulations revealed uniform coolant distribution at the core inlet, with peripheral assemblies exhibiting higher flow rates, consistent with previous experimental observations. Quantitative metrics such as the coefficient of variation (COV), relative error (RD), and root mean square error (RMSE) confirmed the superior performance of the SST model in CFX, achieving a COV of 7.993% (experimental COV: 5.694%) and an RD of 0.047. This methodology not only validates the CFD approach but also highlights its applicability to reactor design optimization and safety assessment. The findings of this study provide critical guidelines for analyzing complex thermal-fluid systems in nuclear reactor designs.

Small leaks within a nuclear power plant can escalate into significant leaks, leading to plant shutdown and substantial losses if operational limits are exceeded. Thus, the demand for systems that can rapidly detect minor leaks is increasing. Current research seeks to address this need. Understanding the thermal–hydraulic features of these systems is crucial for their evolution. In this study, we designed a numerical analysis process to evaluate a prototype leak detection system simulator. We devised a numerical model to simulate leaks and subsequently conducted a bifurcated computational fluid dynamics analysis to assess its viability. First, we examined the leak dynamics within the insulation, focusing on the effects of the gap between the pipe’s insulation and its external casing. The findings from the initial analysis informed the conditions for studying the collection loop. The assessment highlighted a shift in relative humidity downstream of the collection loop, mirroring experimental observations. The results suggest that the newly developed small leak detection system can effectively detect leaks by collecting the escaping fluid through a collection loop and analyzing variations in relative humidity when a small leak occurs in the high-pressure piping of a nuclear power plant. These findings have been instrumental in developing a collection loop experimental apparatus, which will further elucidate the heat transfer dynamics during its operation.

The APR1000 (Advanced Power Reactor 1000) is a next-generation pressurized water reactor (PWR) developed from the APR1400 design, featuring enhanced safety and compliance with European Utility Requirements (EUR) for European market entry. Accurate flow distribution at the reactor core inlet is essential for maintaining safety indicators such as cooling performance, DNBR, and thermal margin. This study establishes and validates a computational fluid dynamics (CFD) methodology to predict the core inlet flow distribution of the APR1000 reactor. A 1/5 scaled experimental model was constructed, and CFD simulations were conducted using ANSYS FLUENT and ANSYS CFX software. Various grid densities and turbulence models—including Standard k-ε, SST, RNG k-ε, and Reynolds Stress Model (RSM)—were evaluated f or their impact on flow accuracy. Grid sensitivity analysis showed that even coarse grids provided reliable results, enhancing computational efficiency without significant loss of accuracy. Among the turbulence models, SST and RNG k-ε showed the best agreement with experimental data. Notably, the SST model in ANSYS CFX achieved the highest correlation with experimental results, demonstrating the lowest RMSE and MAE values compared to ANSYS FLUENT. These findings confirm the robustness of the developed CFD methodology for APR1000 design and safety assessments, supporting optimized reactor design and reducing the risk of intellectual property disputes during international expansion. Future research will explore a wider range of operating conditions and emergency scenarios to further enhance CFD-based safety analyses for advanced nuclear reactors.

Owing to pipe thinning, fatigue damage, and aging, pipes, valves, and devices installed in the primary and secondary systems of nuclear power plants may leak high-temperature/high-pressure reactor coolant. Thus, a system must be developed to determine if the leakage is exceeding the operating limit of the nuclear power plant, thereby mitigating any loss of life or economic loss in such cases. In this study, a validated numerical analysis method was established to initially simulate the leakage behavior and subsequently to evaluate the small amount of leakage in the compartment. For this purpose, a vapor-jet collision test in the compartment and a vapor-jet test in the pipe were performed; numerical analysis was conducted, and comparative analysis was performed to verify the validity of the established method. The evaluation results suggested that the proposed numerical analysis method could optimally simulate the flow characteristics of the steam jet. Notably, compared to the existing evaluation method, the proposed approach simulated a more detailed behavior of the jet formed at the leakage point. In future research, the results of this study (data) will be used to inform the design of the second phase of the leak-capture system and will be served as the foundation for a performance-optimization study on the capture system.

Suppose a small amount of leakage exceeds the limit of the operating conditions of a nuclear power plant. In that case, losses due to the nuclear power plant shutdown may occur, or accidents due to leakage may occur. Consequently, there has been a need to develop a system capable of quickly detecting even small amounts of leakage, and research has been conducted to address this need. To develop such a system, it is necessary to understand the thermal-hydraulic characteristics of the system. This study established a CFD-based evaluation process for evaluating leak detection systems. A numerical analysis model was used to simulate leakage, and a two-step CFD analysis was performed to assess its applicability. In the first step, a study of the leakage behavior in the insulation material was conducted, and the effect of the gap between the pipe insulation material and the outer cover was evaluated. In the second step, the collection loop was analyzed using the results of the leakage behavior analysis in the insulation as an input condition. The results of this study were used to construct the collection loop experimental device and will help in understanding the heat flow characteristics in the collection loop.

The spinal anatomy is composed of a series of motion segments (MSs). Although finite element (FE) analysis has been extensively used to investigate the spinal biomechanics with various simplifications of the spinal structures, it is still a challenge to investigate the interactions of different MSs. Anatomical studies have shown that there are major spine ligaments connecting not only single-MS (i.e., two consecutive vertebrae) but also spanning multi-vertebral bones or multi-MSs. However, the effects of the multi-MS spanning ligaments on the spine biomechanics have not been investigated previously. This study developed an FE model of the lumbar spine by simulating the anterior longitudinal ligaments (ALLs) in two portions, one connecting a single-MS and the other spanning two MSs, with varying physiological cross-sectional area (PCSA) ratios of the two portions. The spine biomechanics during extension motion were investigated. The results showed that on average, the constraining forces by the two-MS spanning elements were ∼18% of those of the single-MS ALL elements when the PCSA ratio was 50%, but the two-MS ALL elements also applied compressive forces on the anterior surfaces of the vertebrae. Decreases in intradiscal pressure were also calculated when the two-MS spanning ALL elements were included in the spine model. The multi-MS spanning ligaments were shown to synergistically function with the single-MS elements in spine biomechanics, especially in the interactions of different MSs. The novel lumbar FE model could therefore provide a useful analysis tool for investigation of physiological functions of the spine.

Mechanical seals, such as labyrinth seals, are typically installed at the turbine outlets to prevent oil leakage. However, these seals undergo deformation because of the vibrations of the rotor, even during normal turbine operating conditions, which may cause an increase in oil leakage. In this study, the oil leakage performance of three labyrinth seals with different types of seal teeth, narrow stainless teeth (Type 1), wide aluminum teeth fixed on the body (Type 2), and fixed wide aluminum movable teeth (Type 3), were evaluated using finite element (FE) and computational fluid dynamics (CFD) analyses. Three-dimensional FE models of the rotor and oil deflectors were developed, and the plastic deformation of the teeth of the labyrinth seals was predicted when the rotor impacted the sealing teeth during turbine operation. The oil leakage was predicted using CFD analysis. The results indicated that the Type 3 seal, including movable teeth, is beneficial in preventing leakage and tooth deformation compared with the other types. The Type 2 seal is advantageous because it results in a smaller increase in gap size and greater vena contracta effects than the Type 1 seal. The results of this study could be helpful when designing and selecting the teeth of a labyrinth seal.

The rupturing of steam generator tubes leads to serious accidents in nuclear power plants. It causes radioactive materials to leak into the secondary system and release outside the reactor containment region. Therefore, it is important to model a technique to determine whether the natural circulation within a reactor coolant system (RCS) can cause rupture. In this study, a computational fluid dynamics (CFD) analysis methodology was incorporated as a first step to establish an RCS natural circulation evaluation technique to generate RCS natural circulation input parameters for the MELCOR analysis of thermally induced steam generator tube rupture (TI-SGTR) in nuclear power plants. Benchmarking tests were conducted against existing experimental studies; the results demonstrated a difference of 9.4% or less between the experimental and CFD analysis results with respect to the main evaluation factors. Subsequently, a steam generator tube simplification modeling technique was established for application to nuclear power plants, and CFD analysis was conducted to determine its applicability. The CFD analysis results revealed that when numerous tubes are simplified into one equivalent tube, the thermal flow characteristics generated in the RCS could be distorted. The findings of this research are expected to be helpful in understanding the thermal flow characteristics of natural circulation in the RCS. Further, the findings may potentially serve as a foundation for future CFD analysis research related to the natural circulation in the RCS of nuclear power plants.

A correction to this paper has been published: https://doi.org/10.1007/s12541-021-00543-9

Extragraft bone formation is crucial for obtaining a successful outcome after spinal fusion surgery. However, the cause of bone formation is not well investigated. In this study, it was hypothesised that extragraft bone formation is generated by mechanical stimuli. A preoperative plan for anterior cervical discectomy and fusion was applied to the finite element model of the C5–C6 motion segment. Extragraft bone formations posterior to the interbody cage were simulated using simultaneous and sequential algorithms. While the simultaneous algorithm predicted the formation of extragraft bone bridging under flexion and extension, the bridge was generated only under extension with the sequential algorithm. This was caused by an ill-defined design space in cases where the simultaneous algorithm was used. Our results using the sequential algorithm show how the progress of extragraft bone formation affects spine mechanics, and our results support the hypothesis that a mechanical stimulus is a major factor influencing extragraft bone formation.

Computational models and inverse dynamic optimization methods are used to predict in-vivo spinal loading. Spinal force is conventionally predicted using the constant loading path method, which is based on the concept that the physiological directions of the spine loads follow the same path of the spinal curve. However, the global convergence optimization method, in which the instantaneous center of rotation of the joint should be also predicted, is necessary for accurate prediction of joint forces of the human body. In this study, we investigate the joint forces, instantaneous centers of rotation, and muscle forces of the human lumbar spine using both global convergence optimization method and constant loading path method during flexion, upright standing, and extension postures. The joint forces predicted using the constant loading path method were 130%, 234%, and 253% greater than those predicted using the global convergence optimization method for the three postures. The instantaneous centers of rotation predicted using the global convergence optimization method were segment level-dependent and moved anteriorly in the flexion and posteriorly in the extension, whereas those predicted using the constant loading path method moved posteriorly in both the flexion and extension. The data indicated that compared to the global convergence optimization method, the constant loading path method introduces additional constraints to the spinal joint model, and thus, it results in greater joint and muscle forces.

The accurate assessment of the major equipment including the spent fuel storage rack and pool in the nuclear power plant is getting more important and its high resistance against the earthquake is in demand also, with the occurrence of major earthquakes in recent years [1,2]. Spent fuel storage rack is equipment temporarily storing spent fuel assemblies, which are removed from the nuclear reactor before they are moved to the dry cask storage. The rack is not fixed but is free standing on the bottom plane of the pool. The rack can slide on the pool floor as well as tilt in case that a strong motion including the earthquake is applied to the pool. The rack potentially impacts the adjacent racks, pool walls, and/or pool floor. Therefore, investigation of the motion of the rack is very critical in seismic assessment of the spent fuel pool. The free-standing rack is submerged in the coolant. The rack is accelerated, in case of a postulated strong motion such as the earthquake, not only by the motion of the pool because of the earthquake, but also by the hydrodynamic fluid-structure interaction (FSI) which is induced by the coolant surrounding the rack [2–6]. Adequate assumption and formulation for FSI are very critical for the accurate seismic assessment of the spent fuel storage rack and pool. Hydrodynamic effects of the fluid on the submerged object have been classified into fluid inertia effects, sloshing effect, fluid elasticity effect, and damping effect [6]. The inertia effect of the coolant is considered while the others are generally ignored in seismic assessment of the spent fuel pool [7,8]. However, the rationale of the hypothesis or assumption is not clear. In this study, we investigated the convective effect (or sloshing effect) and impulsive effect (or inertia effect) of the coolant in the spent fuel pool on the storage rack using computational fluid dynamics (CFD) analysis. Then, mechanical behaviors of the racks in the spent fuel pool were investigated and the rack, which showed the highest acceleration, was predicted using finite element (FE) analysis.

Recently, the U.S. Nuclear Regulatory Commission indicated the non-conservativeness of ANSI/ANS 58.2, which is a technical standard for evaluating the jet impingement load owing to the high-energy line break accident in a nuclear power plant. Therefore, it is necessary to develop a new methodology that can accurately evaluate the characteristics of jet impingement load caused by a supersonic steam jet. In this study, a numerical analysis methodology for evaluating this load was developed and verified. In addition, the conservativeness of the ANSI jet model was investigated using the developed methodology. The results showed that the ANSI jet model could not sufficiently consider the physical behavior of the under-expanded steam jet and predicted a lower jet impingement load than the numerical analysis results at certain conditions. Thus, it is necessary to improve the jet impingement load evaluation model or introduce a new evaluation technique.

Predicting the sloshing motion of a coolant during a seismic assessment of a rectangular spent fuel pool is of critical concern. Linear theory, which provides a simple analytical method, has been used to predict the sloshing motion in rectangular pools and tanks. However, this theory is not suitable for the high-frequency excitation problem. In this study, the authors developed a simple analytical method for predicting the sloshing motion in a rectangular pool for a wide range of excitation frequencies. The correlation among the linear theory parameters, influencing on excitation and convective waves, and the excitation frequency is investigated. Sloshing waves in a rectangular pool with several liquid heights are predicted using the original linear theory, a modified linear theory and computational fluid dynamics analysis. The results demonstrate that the developed method can predict sloshing motion over a wide range of excitation frequencies. However, the developed method has the limitations of linear solutions since it neglects the nonlinear features of sloshing motion. Despite these limitations, the authors believe that the developed method can be useful as a simple analytical method for predicting the sloshing motion in a rectangular pool under various external excitations.

Although the clinical importance of extragraft bone formation (ExGBF) and bridging (ExGBB) has been reported, few studies have investigated the biomechanical influences of ExGBF on the motion segment. In this study, ExGBF was simulated at the C5-C6 motion segment after anterior cervical discectomy and fusion using a developed finite element model and a sequential bone-remodelling algorithm in flexion and extension. The computer simulation results showed that extragraft bone was primarily formed in the extension motion and grew to form ExGBB. A stepwise decrease in the intersegmental rotation angle, maximum von Mises stress and strain energy density on the trabecular bone with ExGBF were predicted in extension. When ExGBB was formed in the trabecular bone region, the intersegmental rotation angle slightly decreased with additional bone formation. However, the stress and strain energy density on the trabecular bone region decreased until ExGBB reached the peripheral cortical margin. The results offer a rationale supporting the hypothesis that mechanical stimuli influence ExGBF. ExGBF was helpful in increasing the stability of the motion segment and decreasing the fracture risk of trabecular bones, even in cases in which ExGBB was not formed. ExGBB can be classified as either soft or hard bridging based on a biomechanical point of view.

Spent fuel pools are used as temporary storage for spent fuel assemblies in nuclear power plants and are filled with coolant which removes the decaying heat from spent fuel assemblies. Sloshing of the coolant can occur if an earthquake occurs in the area. It may produce additional forces on the pool or inner structure and cause overflow of the coolant. It is therefore critical to investigate the phenomenon of sloshing in a seismic assessment of the spent fuel pool. The size of an actual spent fuel pool is excessive for carrying out an experimental study; thus, a scale model is necessary for experimentation. In this study, a scaling law was defined for test conditions using a scale model to understand sloshing behavior, and the results were validated via computational fluid dynamic analysis. Because sloshing is resonant in a fluid and the first mode natural frequency of a fluid is dominant in sloshing behavior, the test condition could be obtained based on the natural frequency of the fluid. In the model, which is scaled with a factor of “Sf,” the scale factors “Sf,” “Sf0,” “Sf−0.5,” and “Sf0.5” were used for displacement, acceleration, excitation frequency, and excitation time, respectively. Approximately 5% difference in maximum sloshing height between two models was predicted in the only case that 1/8 and 1/4 models (1/8 and 1/4 scaled down from an actual spent fuel pool) were excited with 10 Hz and 7.071 Hz, respectively, but the same sloshing height and pressure were predicted in other cases. The results of this study support the idea that the Froude scaling law can be used when using a scale model for a seismic assessment of spent fuel pools to investigate sloshing behavior.

The X-ray-based reconstruction methods using anterior-posterior (AP) and lateral (LAT) images assumes that the angle between the AP and LAT images is perpendicular. However, it is difficult to maintain the perfect perpendicular angle between the AP and LAT images when taking those two images sequentially in real situations. In this study, the robustness of a three-dimensional (3D) whole spine reconstruction method using AP and LAT planar X-ray images was analyzed by investigating cases in which the AP and LAT images were not taken perpendicularly. 3D models of the patient-specific spine from five subjects were reconstructed using AP and LAT X-Ray images and the 3D template models of C1 to L5 vertebrae based on B-spline free-form deformation (FFD) technology. The shape error, projected area error, and relative error in length were quantified by comparing the reconstructed model (FFD model) to the reference model (CT model). The results indicated that the reconstruction method might be considered robust in case that there is a small angular error, such as 5°, between the AP and LAT images. This study suggested that simple technical indications to obtain the perpendicular AP and LAT images in real situations can improve accuracy of 3D spine reconstruction.

It is critical to predict the rack motions subject to the seismic load in the seismic assessment of the spent fuel pool (SFP), because the collisions among racks or between racks and spent fuel pool might cause damages on the SFP, racks, and spent fuel assemblies. To predict the rack motions subject to the external excitation such like seismic force, several method, including analytical method, multibody-dynamic simulation, and finite element analysis could be used. The motions of the rack in the SFP is the resultant motion of the complex physics of the external load including seismic force, convection of the fluid filled in the SFP, and friction between racks and liner of the SFP. Thus, to estimate the rack motion subject to seismic load, the fluid structure interaction is necessary. Commercial finite element analysis software such as Ansys Mechanical (Ansys Inc., Canonsburg, PA, USA) and Abaqus (Simulia, Providence, RI, USA) could be used for estimating the rack motions, because they support fluid structure interaction. However, it has not been reported how the commercial software predicts the rack motion subject to the external excitation, and different software might estimate different rack motions. In this study, as a first study to estimate rack motion in the SFP, the rack motions subject to several periodic external excitations were predicted with neglecting fluid effects using two commercial software Ansys Mechanical and Abaqus, and the results were compared with each other and with analytical results.