Validation and Application of the Thermal Hydraulic System Code TRACE for Analysis of BWR Transients

Good quality experimental data is needed to refine the thermal hydraulic models for the prediction of rod bundle void distribution and critical heat flux (CHF) or dry-out. The Nuclear Power Engineering Corporation (NUPEC) has provided a valuable database to evaluate the thermal hydraulic codes [1]. Part of this database was selected for the NUPEC BWR Full-size Fine-Mesh Bundle Tests (BFBT) benchmark sponsored by US NRC, METI-Japan, NEA/OECD and Nuclear Engineering Program of the Pennsylvania State University (PSU). Twenty-five organizations from ten countries have confirmed their intention to participate and will provide code predictions to be compared to the measured data for a series of defined exercises within the framework of the BFBT benchmark. This benchmark data includes both the fine-mesh high quality sub-channel void fraction and critical power data. Using a full BWR rod bundle test facility, the void distribution was measured at mesh sizes smaller than the sub-channel by using a state-of-the-art computer tomography (CT) technology [1]. Experiments were performed for different pressures, flow rates, exit qualities, inlet sub-cooling, power distributions, spacer types and assembly designs. There are microscopic and sub-channel averaged void fraction data from the CT scanner at the bundle exit as well as X-ray densitometer void distribution data at different elevation levels in the rod bundle. Each sub-channel’s loss coefficient was calculated with using the Rehme method [2,3], and a COBRA-TF sub-channel model was developed for the NUPEC facility. The BWR assembly that was modeled with COBRA-TF includes two water rods at the center. The predicted sub-channel void fraction values from COBRA-TF are compared with the bundle exit void fraction values measured using the CT-scanner void fraction from the BFBT benchmark data. Different plots are used to examine the code prediction of the void distribution at a sub-channel level for the different sub-channels within the bundle.

Existing doping detection strategies rely on direct and indirect biochemical measurement methods focused on detecting banned substances, their metabolites, or biomarkers related to their use. However, the goal of doping is to improve performance, and yet evidence from performance data is not considered by these strategies. The emergence of portable sensors for measuring exercise intensities and of player tracking technologies may enable the widespread collection of performance data. How these data should be used for doping detection is an open question. Herein, we review the basis by which performance models could be used for doping detection, followed by critically reviewing the potential of the critical power (CP) model as a prototypical performance model that could be used in this regard. Performance models are mathematical representations of performance data specific to the athlete. Some models feature parameters with physiological interpretations, changes to which may provide clues regarding the specific doping method. The CP model is a simple model of the power-duration curve and features two physiologically interpretable parameters, CP and W′. We argue that the CP model could be useful for doping detection mainly based on the predictable sensitivities of its parameters to ergogenic aids and other performance-enhancing interventions. However, our argument is counterbalanced by the existence of important limitations and unresolved questions that need to be addressed before the model is used for doping detection. We conclude by providing a simple worked example showing how it could be used and propose recommendations for its implementation.

Uncertainty and sensitivity analyses as a validation tool for BWR bundle thermal–hydraulic predictions

Validation of CTF pressure drop and void predictions for the NUPEC BWR database

Two-phase pressure drop and void fraction in a cross-corrugated plate heat exchanger channel: Impact of flow direction and gas-liquid distribution

Best estimate system thermal-hydraulic codes in the nuclear engineering community, e.g., TRACE, RELAP3D, CATHARE-3, etc., were extended with 3D coarse-mesh components to better describe the 3D Thermal-Hydraulic (TH) phenomena taking place within the Reactor Pressure Vessel (RPV) and the core. The RPV is usually shaped like a cylinder while the core is mostly a cube. Hence, the TRACE code is equipped with a Cylindrical VESSEL and a Cartesian VESSEL. The former one is to represent the RPV (including core), pressurizer, and steam generator. The latter one is more appropriate to represent the core. The two components are connected by two Vessel-Junctions (VJ) at the core inlet and outlet. Due to the different nodalization between the two VESSELs, the analyst needs to do repetitive and error-prone work defining the cell-to-cell junctions and their TH parameters. To facilitate this process, the Karlsruhe Institute of Technology (KIT) has developed an automatic approach based on a mesh-constructing and field-mapping library, namely the MEDCoupling. These new capabilities of TRACE are demonstrated by the analysis of the coolant mixing for an academic case and the AP1000 reactor.

Resistance training and exercise tolerance during high-intensity exercise: moving beyond just running economy and muscle strength.

Critical velocity (CV) and critical power (CP) have been proposed to be effective indirect anaerobic threshold methods in monitoring training and predicting performance of rowing, respectively. However, which index is the most proper one when applying critical concept in rowing performance is not clear. Purpose To compare the two indexes in predicting indoor rowing performance by combining different physiological variables, including maximal oxygen uptake (VO2max), anaerobic threshold (OBLA) and modified Wingate test, which are important physiological variables in endurance performance. Method Fifteen elite female rowers (age 20.7 ± 1.4 years, height 1.64 ± 0.35m, weight 56.64 ± 4.38kg) were recruited in this study. VO2max (43.31 ± 5.25ml/kg/min) and OBLA (157.81 ± 22.08W) were measured during a discontinuous graded exercise test, starting at 100W, on a Concept II ergometer increased by 25 W for each 3 min stage. Four test times of duration 90s, 240s, 600s, and 1200s were used to determine CP (139.49 ± 20.37W), and CV(4.00 ± 0.14m/s) was estimated by 400m, 600m, 800m, 1000m maximal exertion trials on different days as well by using Linear distance-time model. Peak power (353.48 ± 27.71W), maximum power (350.12 ± 26.72W), minimum power (336.85 ± 21.58W), mean power (314.44 ± 27.87W), fatigue index [(max power – min power)/mean power] were obtained using a modified Wingate test protocol (30s sprint) on the ergometer. Result The results showed that VO2max, OBLA, CP, CV, peak power, mean power were significantly correlated with 2000m indoor rowing performance (r=−0.84, −0.85, −0.81, −0.97, −0.66, −0.67, p<0.01). By submitting mean power, fatigue index, VO2max, OBLA with each index to a stepwise regression analysis, it produced two individual critical concept models as following to predict 2000m indoor rowing performance:CV model: Time for 2000m=−131.44(CV)-89.57(fatigue) index+1022.27 (R2 = 0.96, SEE=4.08, p<0.05); CP model: Time for 2000m = −0.445(OBLA) −1.853(VO2max) +643.98 (R2 = 0.84, SEE=7.75, p<0.05). Conclusion Our findings in this study indicated that in the CV model, CV has more predictive power, represented as anaerobic threshold, than OBLA to predict rowing performance. Besides CV, fatigue index from modified Wingate test explains an additional 15 % variance in rowing performance. Therefore, compared with CP, CV could be used when applying critical concept in training and evaluate indoor performance in rowing.

A two-phase flow is the simplest form of multi-phase flow. Two-phase flow has basic parameters, including flow behavior, flow pattern, void fraction, pressure gradient, or pressure drop. The development and application of fluid flow in small channels (mini and micro) are in the Micro Electromechanical System (MEMS). In general, the application of two-phase flow can be found in various applications in the industrial world, such as boilers, cores, and steam generators in nuclear reactors, petroleum transportation, electronic cooling, and different other types of chemical reactors. One of the most common challenges is void fractions and flow patterns in horizontal and vertical pipelines. The purpose of this study was to find out the significant difference in the characteristic value of fundamental parameters, primarily void fractions and flow patterns that occur in capillary pipes with a slope of 15o to horizontal. The fraction value and shape of this flow pattern are essential because it determines the pressure drop value, which means determining the level of danger that can occur if the pressure drop value reaches the extreme value. The fluid used a mixture of air-water and glycerin with 0, 10, 20, and 30% concentrations. To determine the void fraction is used digital image processing method with MATLAB R2014a application. A 1200 fps high-speed camera and 640 x 480-pixel resolution are used for video shooting. The experiment was conducted at superficial gas (JG) velocities of 0.025 - 66.3 m/s and superficial fluid velocities (JG) intervals of 0.033 – 4.935 m/s. The experiment results showed a significant difference between the void fraction value for the bubbly flow pattern and the churn flow pattern, which has not been widely discussed in previous studies. The analysis concluded that the higher the velocity of superficial gases, the void fraction value increases. This increase in the void fraction is why there is a significant change in flow patterns from bubble flow patterns to churn. In addition, it was also found that the increased viscosity of the fluid significantly affected changes in flow patterns, incredibly bubbly and plug, but its velocity decreased. It is also the result that the higher homogeneous void fraction (β) value affects the increase in the length of bubbly flow patterns and plugs.

Bubble behavior in narrow channel can be quite different with that in conventional channel. When the bubble reaches a size which is comparable with the channel dimension, the bubble is confined by the channel wall. This influences the bubble evolution significantly in the narrow channel. Then the characteristics of pressure drop in the narrow channel is affected significantly. In order to investigate the effect of bubble behavior on flow boiling pressure drop, a visual study was carried out with a high speed camera (5,000 frame per second was used) to record the bubble behavior. It is found that the OSV (Onset of Significant Vapor) emerges much earlier in narrow channel when comparing with that in conventional channel. A revised correlation for prediction of the real void fraction is proposed based on the experimental investigation. It is also found that the bubble behavior affects the pressure drop in narrow channel significantly, and the channel will be blocked easily when the confined vapor cluster appears. The pressure drop, however, dose not increase linearly with increasing void fraction, and the minimum pressure drop occurs with 60% void fraction. With increasing void fraction, the bubble behavior is more intense and turbulent, which induces more severe fluctuation in pressure drop.

CORETRAN-01 is the Electric Power Research Institute core analysis computer program that couples the neutronic code ARROTTA to the thermal-hydraulic code VIPRE-02 to achieve an integrated three-dimensional representation of the core for both steady-state and transient applications. The thermal-hydraulic module VIPRE-02, the two-fluid version of the one-fluid code VIPRE-01, has been the object of relatively few assessment studies, and the work presented seeks to reduce this lacuna. The priority has been given to the assessment of the void fraction prediction due to the importance of the void feedback on the core power generation. The assessment data are experimental void fractions obtained from X- and gamma-ray attenuation techniques applied at assembly-averaged as well as subchannel level for both steady-state and transient conditions. These experiments are part of the NUPEC (Japan) program where full-scale boiling water reactor (BWR) assemblies of different types, including assemblies with part-length rods, and pressurized water reactor subassemblies were tested at nominal reactor operating conditions, as well as for a range of flow rates and pressures. Generally, the code performance ranged from adequate to good, except for configurations exhibiting a strong gradient in power-to-flow ratio. Critical power predictions have also been assessed and code limitations identified, based on measurements on full-scale BWR 8 × 8 and high-burnup assemblies operated over a range of thermal-hydraulic conditions.

In recent years, extensive thermal-hydraulic experimental tests have been performed on the lead-bismuth eutectic (LBE)–cooled, wire-wrapped fuel assembly (FA) of MYRRHA. These thermal-hydraulic tests were performed using FA mock-ups in large-scale LBE experimental test facilities at SCK•CEN (Belgium), ENEA (Italy), and Karlsruhe Institute of Technology (Germany). The FA pressure drop characteristics and flow-induced vibration (FIV) characteristics were tested with a full-scale 127-pin mock-up test section. The existing pressure drop correlations of Rehme and of Cheng and Todreas (simplified model) predict the experimental pressure drop data very well and are considered suitable for use in the design and safety analysis of the MYRRHA system. FIVs are very limited in the wire-wrapped bundle, and fuel pin fatigue damage from vibration during operation is not expected. Further analysis and testing are required to determine if damage from fretting corrosion could be expected.Heat transfer characteristics of the FA were investigated experimentally in two separate 19-pin heated rod test sections cooled by LBE. The existing Kazimi-Carelli correlation predicts the global average Nusselt numbers very well, but the correlation is not developed to capture local hot spots. For the FA safety analysis, to further determine operational safety margins, a hot-spot factor is defined and analyzed to determine the hot-spot temperature penalty.

The TRITON11® fuel design is the latest advancement in boiling water reactor (BWR) fuel technology from Westinghouse, developed to improve fuel cycle economics, thermal performance, and reliability compared to previous designs. This paper provides a comprehensive overview of the thermal-hydraulic testing and modeling efforts supporting the qualification and licensing of the TRITON11 fuel, along with recent innovations related to BWR core thermal-hydraulics. Extensive experimental activities were conducted at the Westinghouse fuel thermal-hydraulic laboratory using the FRODE and FRIGG loops, which simulate prototypical BWR operating conditions. Key tests included critical boiling transition, pressure drop, void fraction, and hydraulic axial force measurements. Additionally, recent tests supporting the development of the new StrongHold ® debris filter are discussed. In parallel, Westinghouse advanced core simulation and subchannel analysis tools (POLCA7/POLCA8 and MEFISTO-T) were further developed, allowing accurate predictions of complex core flow distribution, critical power performance, bundle lift force, and moderator density. The MEFISTO-T code integrates advanced two-phase flow models, in addition to a novel four-field model of annular two-phase flow, explicitly accounting for disturbance waves, along with a multifield transport model of reactor coolant impurities. These models have been validated against experimental data, demonstrating reliable predictive capabilities for critical power and newly observed localized impurity deposition under BWR core conditions. The combined results from these thermal-hydraulic testing and modeling efforts contribute to improved operational flexibility and reliability of Westinghouse BWR fuel designs and support the accurate evaluation of safety margins.

Based on the experiments carried out over the past decade at microgravity conditions, an overview of our current knowledge of bubbly and slug flows is presented. The transition from bubble to slug flow, the void fraction and the pressure drop are discussed from the data collected in the literature. The transition from bubble to slug flow may be predicted by introducing a critical void fraction that depends on the fluid properties and the pipe diameter; however, the role of coalescence which controls this transition is not clearly understood. The void fraction may be accurately calculated using a drift-flux model. It is shown from local measurements that the drift of the gas with respect to the mixture is due to non-uniform radial distribution of void fraction. The pressure drop happens to be controlled by the liquid flow for bubbly flow whereas for slug flow the experimental results show that pressure drops is larger than expected. From this study, the guidelines for future research in microgravity are given.

PurposeThis study examined the relationship of physiological and anthropometric characteristics with parameters of the critical power (CP) model, and in particular the reconstitution of W′ following successive bouts of maximal exercise, amongst trained and untrained cyclists.MethodsTwenty male adults (trained nine; untrained 11; age 39 ± 15 year; mass 74.7 ± 8.7 kg; V̇O2max 58.0 ± 8.7 mL kg−1 min−1) completed three incremental ramps (20 W min−1) to exhaustion interspersed with 2-min recoveries. Pearson’s correlation coefficients were used to assess relationships for W′ reconstitution after the first recovery (W′rec1), the delta in W′ reconstituted between recoveries (∆W′rec), CP and W′.ResultsCP was strongly related to V̇O2max for both trained (r = 0.82) and untrained participants (r = 0.71), whereas W′ was related to V̇O2max when both groups were considered together (r = 0.54). W′rec1 was strongly related to V̇O2max for the trained (r = 0.81) but not untrained (r = 0.18); similarly, ∆W′rec was strongly related to V̇O2max (r = − 0.85) and CP (r = − 0.71) in the trained group only.ConclusionsNotable physiological relationships between parameters of aerobic fitness and the measurements of W′ reconstitution were observed, which differed among groups. The amount of W′ reconstitution and the maintenance of W′ reconstitution that occurred with repeated bouts of maximal exercise were found to be related to key measures of aerobic fitness such as CP and V̇O2max. This data demonstrates that trained cyclists wishing to improve their rate of W′ reconstitution following repeated efforts should focus training on improving key aspects of aerobic fitness such as V̇O2max and CP.