scholarly journals Effect of inserted sphere size on heat transfer characteristics of FCC structured pebble bed in a HTGR

2019 ◽  
Vol 128 ◽  
pp. 03004 ◽  
Author(s):  
Leisheng Chen ◽  
Jaeyoung Lee
Keyword(s):  
Heat Transfer ◽  
Hot Spots ◽  
Maximum Velocity ◽  
Severe Accident ◽  
Sphere Diameter ◽  
Face Centered Cubic ◽  
Heat Transfer Characteristics ◽  
Pebble Bed ◽  
Small Sphere ◽  
Face Centered

Hot spots appearing in an operating high temperature gas-cooled reactor (HTGR) core have been considered as the most possible reason leading to a severe accident like fission production releasing to the environment, therefore, investigation on their positions and thus seeking ways to reduce the possibility of their appearance have attracted scientists’ attention. In our previous studies, heat transfercharacteristics of a face–centered–cubic (FCC) structured pebble–bed have been discussed,and a correlation on heat transfer coefficient with Reynolds number was presented. In this study, a method, placing a small sphere in thegap area, which is able to enhance the convective heat transfer wasproposed and the effect verifiedas well. The influence of the sphere diameter on heat transfer performances wasinvestigated in details. It is concluded through results analysis that (1) inserted sphere lowered thelocal surface temperature of adjacent pebbles by varying surrounding flow field;(2) maximum velocity of the fluid and average heat transfer coefficientincreased with sphere diameter, particularly, comparing with no small sphere case, 12.95% enhancement was achieved. Such findings may provide dataand information for reactor designers, andhelp to develop a safer HTGR pebble–bedcore.

scholarly journals Numerical Study on the Thermal Field and Heat Transfer Characteristics of a Hexagonal-Close-Packed Pebble Bed

Computation ◽  
2022 ◽  
Vol 10 (1) ◽  
pp. 1
Author(s):  
Leisheng Chen ◽  
Jiahao Zhao ◽  
Yuejin Yuan ◽  
Jaeyoung Lee
Keyword(s):  
Heat Transfer ◽  
Numerical Study ◽  
Face Centered Cubic ◽  
Heat Transfer Characteristics ◽  
Transfer Coefficients ◽  
Pebble Bed ◽  
Hexagonal Close Packed ◽  
Transfer Characteristics ◽  
Contact Points ◽  
Hcp Structure

Fuel elements in a high-temperature gas-cooled reactor (HTGR) core may be stacked with a hexagonal close-packed (HCP) structure; therefore, analyzing the temperature distribution and heat transfer efficiency in the HCP pebble bed is of great significance to the design and safety of HTGR cores. In this study, the heat transfer characteristics of an HCP pebble bed are studied using CFD. The thermal fields and convective heat transfer coefficients under different coolant inlet velocities are obtained, and the velocity fields in the gap areas are also analyzed in different planes. It is found that the strongest heat transfer is shown near the right vertices of the top and bottom spheres, while the weakest heat transfer takes place in areas near the contact points where no fluid flows over; in addition, the correlation of the overall heat transfer coefficient with the Reynolds number is proposed as havg = 0.1545(k/L)Re0.8 (Pr = 0.712, 1.6 × 104 ≤ Re ≤ 4 × 104). It is also found that the heat transfer intensity of the HCP structure is weaker than that of the face-centered-cubic structure. These findings provide a reference for reactor designers and will contribute to the development of safer pebble-bed cores.

scholarly journals Свойства движущихся дискретных бризеров в бериллии

2018 ◽  
Vol 60 (5) ◽  
pp. 978
Author(s):  
O.B. Бачурина ◽  
P.T. Мурзаев ◽  
A.C. Семенов ◽  
E.A. Корзникова ◽  
C.B. Дмитриев
Keyword(s):  
Energy Transport ◽  
Interatomic Potential ◽  
Maximum Velocity ◽  
Face Centered Cubic ◽  
Sound Waves ◽  
Many Body ◽  
Hexagonal Close Packed ◽  
Bcc Lattice ◽  
Face Centered ◽  
The Many

AbstractDiscrete breathers (DBs) have been described among pure metals with face-centered cubic (FCC) and body-centered cubic (BCC) lattice, but for hexagonal close-packed (HCP) metals, their properties are little studied. In this paper, the properties of standing and moving DBs in beryllium HCP metal are analyzed by the molecular dynamics method using the many-body interatomic potential. It is shown that the DB is localized in a close-packed atomic row in the basal plane, while oscillations with a large amplitude along the close-packed row are made by two or three atoms, moving in antiphase with the nearest neighbors. Dependences of the DB frequency on the amplitude, as well as the velocity of the DB on its amplitude and on parameter δ, which determines the phase difference of the oscillations of neighboring atoms, are obtained. The maximum velocity of the DB movement in beryllium reaches 4.35 km/s, which is 33.7% of the velocity of longitudinal sound waves. The obtained results supplement our concepts about the mechanisms of localization and energy transport in HCP metals.

Research on Heat Transfer Characteristics of the Thermometric Sphere in HTR-10

2018 ◽  
Author(s):  
Shiyan Sun ◽  
Youjie Zhang ◽  
Yanhua Zheng ◽  
Xiang Fang ◽  
Xiaoyong Yang
Keyword(s):  
Heat Transfer ◽  
Thermal Equilibrium ◽  
Reactor Core ◽  
Fluid Temperature ◽  
Heat Transfer Characteristics ◽  
Pebble Bed ◽  
The Core ◽  
Temperature Measuring ◽  
Transfer Characteristics ◽  
Metal Wires

During the operation of the High Temperature Gas-cooled Reactor (HTGR), the hot-spot temperature in the reactor core must be lower than the maximum permissible temperature of the fuel elements and the materials of construction, so that the reactor kept safe. However, no fixed temperature-measuring devices can be set in a pebble-bed core. A special spherical temperature-measuring device is adopted to make sure it brings as small impact to the reactor operation as possible. There are several metal wires with different melting points inside. The graphite thermometric balls will be put onto the top of HTR-10 reactor core, and they record and reflect the highest temperature in different positions in the core when flowing in the pebble bed. Before the reactor core temperature-measuring experiment of HTR-10, we must study the heat transfer characteristics of the graphite thermometric sphere to find out the relationship of the melting conditions and the temperature in the reactor core. A 3-D model of the graphite thermometric ball is established, and CFD method is adopted to research and figure out the thermal equilibrium time and temperature difference between the metal wires in the ball and the hot fluid outside the balls. Multiple situations are simulated, and the heat transfer process of the thermometric sphere is comprehensively studied. The heat convection is certified the most important aspect. Thermal equilibrium can be achieved within 19 minutes, far shorter than the period while the spheres flowing through the core. The simulation results can also applied to derive the thermal fluid temperature backward.

Numerical Investigation of Heat Transfer Characteristics of Debris Bed After Severe Accident of SFR Based on 1-D Heat Conduction Model

2018 ◽  
Author(s):  
Mengwei Zhang ◽  
Bin Zhang ◽  
Jianqiang Shan
Keyword(s):  
Heat Transfer ◽  
Heat Conduction ◽  
Transfer Process ◽  
Severe Accident ◽  
Heat Transfer Characteristics ◽  
Conduction Model ◽  
One Dimensional ◽  
The Core ◽  
Transfer Characteristics ◽  
Core Catcher

Nuclear reactor severe accidents can lead to the release of a large amount of radioactive material and cause immense disaster to the environment. Since the Fukushima nuclear accident in Japan, the severe accident research has drawn worldwide attention. Based on the one-dimensional heat conduction model, a DEBRIS-HT program for analyzing the heat transfer characteristics of a debris bed after a severe accident of a sodium-cooled fast reactor was developed. The basic idea of the DEBRIS-HT program is to simplify the complex energy transfer process in the debris bed to a simple one-dimensional heat transfer problem by solving the equivalent thermal conductivity in different situations. In this paper, the DEBRIS-HT program code is prepared by using the existing model and compared with the experimental results. The results show that the DEBRIS-HT program can correctly predict the heat transfer process in the fragment bed. In addition, the heat transfer characteristics analysis program is also used to model the core catcher of the China fast reactor. Firstly, the dryout heat flux when all of molten core dropped on the core catcher was calculated, which was compared with the result of Lipinski’s zero dimensional model, and the error between two values is only 11.2%. Then, the temperature distribution was calculated with the heat power of 15MW.

Flow Visualization of Pebble Bed HTGR

2008 ◽  
Author(s):  
Jae-Young Lee ◽  
Sa-Ya Lee
Keyword(s):  
Three Dimensional ◽  
Particle Identification ◽  
Face Centered Cubic ◽  
Mean Flow ◽  
Pebble Bed ◽  
Stagnation Points ◽  
Image Velocimetry ◽  
Flow Geometry ◽  
Computational Fluid Dynamics Cfd ◽  
Face Centered

The nuclear core of High Temperature Gas Reactor (HTGR) with pebble bed type has been investigated intensively due to its benefits in management, but its complicated flow geometry requested the reliable analytical method. Recent studies have been made using the three dimensional computational methods but they need to be evaluated with the experimental data. Due to the complicated and narrow flow channel, the intrusive methods of flow measurement are not proper in the study. In the present study, we developed a wind tunnel for the pebble bed geometry in the structure of Face Centered Cubic (FCC) and measure the flow field using the Particle Image Velocimetry (PIV) directly. Due to the limitation of the image harnessing speed and accessibility of the light for particle identification, the system is scaled up to reduce the mean flow velocity by keeping the same Reynolds number of the HTGR. The velocity fields are successfully determined to identify the stagnation points suspected to produce hot spots on the surface of the pebble. It is expected that the present data is useful to evaluate the three dimensional Computational Fluid Dynamics (CFD) analysis. Furthermore, It would provide an insight of experimental method if the present results are compared by those of scaled down and liquid medium.

Calculation of Turbulent Kinetic Energy Budgets for Flow Through a Pebble Bed Using DNS

2016 ◽  
Author(s):  
Lambert H. Fick ◽  
Elia Merzari ◽  
Yassin A. Hassan
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Navier Stokes ◽  
Energy Budgets ◽  
High Fidelity ◽  
Face Centered Cubic ◽  
Pebble Bed ◽  
Data Set ◽  
Closure Models ◽  
Face Centered

Pebble bed high temperature reactors (PBR) are currently being investigated as a potential successor for light water reactor based designs in the future. Past analyses of flows through PBR cores using Reynolds averaged Navier-Stokes (RANS) approaches have had limited success. Due to a lack of available high fidelity experimental or computational data, optimization of RANS closure models for these geometries has not been extensively done. In the present study, direct numerical simulation (DNS) is employed to develop a high fidelity data set which may be used for the optimization of RANS closure models for pebble bed flows. Calculated parameters include turbulence statistics, as well as values for the turbulent kinetic energy (TKE) budget terms. A well documented, single face centered cubic domain with periodic boundaries was used. Flow was simulated at a Reynolds number of 9308. Tests were conducted to ensure sufficient spatial and temporal resolution for conforming to the requirements for DNS. A selection of the generated statistics and TKE budget terms is presented here.

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