This paper describes an hp-angular adaptivity algorithm in the discrete ordinates method for Boltzmann transport applications with strong angular effects. This adaptivity uses discontinuous finite ...element quadrature sets with different degrees, which updates both angular mesh and the degree of the underlying discontinuous finite element basis functions, allowing different angular local refinement to be applied in space. The regular and goal-based error metrics are considered in this algorithm to locate some regions to be refined. A mapping algorithm derived by moment conservation is developed to pass the angular solution between spatial regions with different quadrature sets. The proposed method is applied to some test problems that demonstrate the ability of this hp-angular adaptivity to resolve complex fluxes with relatively few angular unknowns. Results illustrate that a reduction to approximately 1/50 in quadrature ordinates for a given accuracy compared with uniform angular discretization. This method therefore offers a highly efficient angular adaptivity for investigating difficult particle transport problems.
•Multi-holes steam ejection induced flow and thermal effects for ADS 1–3 are evaluated.•Stratification criteria are combined to predict and assess the thermal stratification.•The improved ADS sparger ...arrangement is recommended to enhance the mixing effects.•Multi-holes lumped “steam condensation column” is modeled to estimate the HTC.
In AP1000 plant, the Automatic Depressurization System (ADS) 1–3 stages operate to discharge the high-temperature and high-pressure steam from the Reactor Coolant System (RCS) primary side to the large heat sink tank In-containment Refueling Water Storage Tank (IRWST) in accidental conditions. The key equipment’s specific shape and arrangement lead to the complicate flow and heat transfer characteristics in IRWST. In the present work, an overall scaled IRWST&ADS sparger experiment has been built up. The thermocouples matrix, flowmeters, pressure transmitters, heat flux sensors, Particle Image Velocimetry (PIV) technique, and high speed camera are employed for the measurements of the key thermal and flow parameters. The local steam jets condensation phenomena as well as the overall flow and thermal behavior are investigated. The experimental results indicate that the thermal stratification phenomenon is obvious in IRWST. The criteria of Richardson Number and Stratification Number are utilized to predict and evaluate the thermal stratification extent, respectively. An improved ADS arrangement design is further proposed to reduce the thermal stratification. Moreover, the multi-holes lumped “steam condensation column” is modeled with characteristic parameters, then the steam condensation heat transfer coefficient range in chugging condensation process is estimated. The experimental results provide practical engineering application reference for the effective operation of the passive safety system in AP1000 plant.
The Fast Flux Test Facility (FFTF) is a liquid sodium-cooled nuclear reactor designed by the Westinghouse Electric Corporation for the U.S. Department of Energy. In July 1986, a series of unprotected ...transients were performed to demonstrate the passive safety of FFTF. Among these, a total of 13 loss-of-flow-without scram (LOFWOS) tests were conducted to confirm the liquid metal reactor safety margins, provide data for computer code validation, and demonstrate the inherent and passive safety benefits of specific design features. In our preliminary work, we have performed relatively coarse modeling of the FFTF. To better predict the transient behavior of FFTF LOFWOS test #13, we modeled it using a more refined thermal-hydraulics model. In this paper, we simulate FFTF LOFWOS test #13 with the system safety analysis code SAC-3D according to the benchmark specifications provided by Argonne National Laboratory (ANL). The simulation range includes the primary and secondary circuits. The reactor core was modeled by the built-in 3D neutronics calculation module and the parallel-channel thermal-hydraulics calculation module. To better predict the reactivity feedback introduced by coolant level variations within the GEMs, a real-time macro cross-section homogenization processing module was developed. The steady-state power distribution was calculated as the transient simulation initial boundary conditions. In general, both the steady-state calculation results and the whole-plant transient behavior predictions are in good agreement with the measured data. The relatively large deviations in transient simulation occur in the outlet temperature predictions of the PIOTA in row 6. It can be preliminarily explained by the reason for neglecting the heat transfer between channels in this model.
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•Small He–V clusters at the surfaces of α-Fe.•The stability characteristics of the He–V clusters.•Formation energy of the clusters on the surface.
The structure and energy of a small ...helium–vacancy (He–V) cluster on the low-index surface of α-Fe are investigated by an ab initio method. We report the stability characteristics of these He–V clusters. The He atom of the He–V cluster at the topmost surface atomic layers (SALs) will relax into the vacuum gap. Some of the surface He atoms at octahedral interstitial sites will relax into a more stable tetrahedral interstitial site. The deformation charge densities and electronic densities of the states explain the instability of the surface He atoms. The formation energies of the He–V clusters gradually increase from the topmost SAL to the bulk-like atomic layer. This indicates that all of the He–V defects considered tend to aggregate at the topmost SAL.
► Temperature fluctuation of triple-jet using LES method was simulated numerically. ► Temperature and velocity characteristics agreed well with the experimental ones. ► Spatial distribution of ...amplitude and frequency of temperature was different. ► Re number did obviously affect temperature fluctuation characteristics.
Temperature fluctuation is caused by the mixing flows out of the core with different temperature in upper plenum. The phenomenon may lead to thermal fatigue in solid structures. In this paper, the parallel triple-jet flows were simulated by the software FLUENT with the large eddy simulation (LES). By comparison, the numerical results were in good agreement with the experimental ones. The flow field observed in simulation showed that many vortices are closely related with the temperature fluctuation phenomenon. From the computed results, it was discovered that amplitudes of temperature fluctuation are different in flow field, while the frequency of temperature fluctuation remains constant at all monitoring position. With the increasing of Reynolds number, the mixing of hot and cold flows is delayed, and convective mixing region is enlarged.
•Experimental investigation on pool boiling of a vertical heated bundle under flooded condition.•Heat transfer coefficients of the bundle under different heated fluxes were obtained.•Flow patterns ...changing with time were recorded.
Heat removal of the spent fuel in the spent fuel pool normally depends on the forced-circulation system in the pool. Once the forced-circulation cooling system fails, decay heat of the spent fuel can only be removed by the natural convection of the coolant. If this situation lasts for a long time, temperature of the water in the pool may continue increasing till the pool-type boiling occurs. It is important to research the boiling heat transfer characteristics for the design and safety assessment of the spent fuel pool. Researches on the pool boiling have already been extensively performed, but few is on the spent fuel assemblies which are vertical, long-span and tight bundles. This paper presents the pool boiling behavior of the heated vertical bundles flooded in the water which models the spent fuel stored in the pool. A series of experiments were carried out with different heated powers. Temperatures of the bundles were measured and heat transfer coefficients were obtained. High-speed camera was used to capture the two-phase flow patterns in the experiments. The highest temperature of the spent fuel cladding is about 115 °C during the saturate boiling state. This datum confirms the safety of the spent fuel under flooded condition.
A three-dimensional, multigroup, diffusion code based on a high order nodal expansion method for hexagonal-z geometry (HNHEX) was developed to perform the neutronic analysis of hexagonal-z geometry. ...In this method, one-dimensional radial and axial spatially flux of each node and energy group are defined as quadratic polynomial expansion and four-order polynomial expansion, respectively. The approximations for one-dimensional radial and axial spatially flux both have second-order accuracy. Moment weighting is used to obtain high order expansion coefficients of the polynomials of one-dimensional radial and axial spatially flux. The partially integrated radial and axial leakages are both approximated by the quadratic polynomial. The coarse-mesh rebalance method with the asymptotic source extrapolation is applied to accelerate the calculation. This code is used for calculation of effective multiplication factor, neutron flux distribution, and power distribution. The numerical calculation in this paper for three-dimensional SNR and VVER 440 benchmark problems demonstrates the accuracy of the code. In addition, the results show that the accuracy of the code is improved by applying quadratic approximation for partially integrated axial leakage and four-order approximation for one-dimensional axial spatially flux in comparison to flat approximation for partially integrated axial leakage and quadratic approximation for one-dimensional axial spatially flux.
► The large amplitude and narrow-band vibration experiment was performed. ► The added mass theory was used to analyze the test plates’ natural vibration characteristics in static water. ► The ...occurring condition of the large amplitude and narrow band vibration was investigated. ► The large amplitude and narrow-band vibration mechanism was investigated.
Further experiments and theoretical analysis were performed to investigate mechanism of the large-amplitude and narrow-band vibration behavior of a flexible flat plate in a rectangular channel. Test plates with different thicknesses were adopted in the FIV experiments. The natural vibration characteristics of the flexible flat plates in air were tested, and the added mass theory of column was used to analyze the flexible flat plates’ natural vibration characteristics in static water. It was found that the natural vibration frequency of a certain test plate in static water is approximately within the main vibration frequency band of the plate when it was induced to vibrate with the large-amplitude and narrow-band in the rectangular channel. It can be concluded that the harmonic between the flowing fluid and the vibrating plate is one of the key reasons to induce the large-amplitude and narrow-band vibration phenomenon. The occurring condition of the phenomenon and some important narrow-band vibration characteristics of a foursquare fix-supported flexible flat plate were investigated.
An experiment was performed to investigate the fluid–structure-coupled dynamic characteristics of the under-water hexagonal fuel assemblies used in a fast reactor. As the dynamic characteristics, the ...added mass and damping caused by fluid–structure interaction (FSI) were usually treated as the constants in the previous researches. By the present experiment, it was proven that the added mass and damping were the variables strongly dependent on the fluid-filled gap between the double hexagonal fuel assemblies. These experimental data can be used as the modeling parameters for the seismic analysis of the core in a fast reactor.
Spent fuel rack is the key equipment for the storage of spent fuel after refueling. In order to investigate the performance of the spent fuel rack under the earthquake, the phenomena including ...sliding, collision, and overturning of the spent fuel rack were studied. An FEM model of spent fuel rack is built to simulate the transient response under seismic loading regarding fluid-structure interaction by ANSYS. Based on D’Alambert’s principle, the equilibriums of force and momentum were established to obtain the critical sliding and overturning accelerations. Then 5 characteristic transient loadings which were designed based on the critical sliding and overturning accelerations were applied to the rack FEM model. Finally, the transient displacement and impact force response of rack with different gap sizes and the supporting leg friction coefficients were analyzed. The result proves the FEM model is applicable for seismic response of spent fuel rack. This paper can guide the design of the future’s fluid-structure interaction experiment for spent fuel rack.
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