Direct Numerical Simulation of the Flow Through a Randomly Packed Pebble Bed

Abstract The proposition for molten salt and high-temperature gas-cooled reactors has increased the focus on the dynamics and physics in randomly packed pebble beds. Research is being conducted on the validity of these designs as a possible contestant for the fourth-generation nuclear power systems. A detailed understanding of the coolant flow behavior is required in order to ensure proper cooling of the reactor core during normal and accident conditions. In order to increase the understanding of the flow through these complex geometries and enhance the accuracy of lower-fidelity modeling, high-fidelity approaches such as direct numerical simulation (DNS) can be utilized. Nek5000, a spectral-element computational fluid dynamics (CFD) code, was used to develop DNS fluid flow data. The flow domain consisted of 147 pebbles enclosed by a bounding wall. In the work presented, the Reynolds numbers ranged from 430 to 1050 based on the pebble diameter and inlet velocity. Characteristics of the flow domain such as volume averaged porosity, axial porosity, and radial porosity were studied and compared with correlations available in the literature. Friction factors from the DNS results for all Reynolds numbers were compared with correlations in the literature. The first- and second-order statistics show good agreement with the available experimental data. Turbulence length scales were analyzed in the flow. Reynolds stress anisotropy was characterized by utilizing invariant analysis. Overall, the results of the analysis in this study provide deeper understanding of the flow behavior and the effect of the wall in packed beds.

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Experimental and Numerical Simulation on Hydraulic Behavior of Molten Flow in the Lower Part in Reactor Core

Volume 5: Student Paper Competition ◽

10.1115/icone24-60572 ◽

2016 ◽

Author(s):

Kota Matsuura ◽

Hideaki Monji ◽

Susumu Yamashita ◽

Hiroyuki Yoshida

Keyword(s):

Numerical Simulation ◽

Liquid Film ◽

High Speed ◽

Nuclear Power ◽

Power Plants ◽

Flow Behavior ◽

Reactor Core ◽

Video Camera ◽

Working Fluid ◽

Simulation Code

In the decommissioning work of nuclear power plants, it is important to grasp the sedimentation place of molten materials. However, the technique to grasp exactly sedimentation place is not established now. Therefore, the detailed and phenomenological numerical simulation code named JUPITER for predicting the molten core behavior is developed. In the study, visualization experiment and numerical simulation were performed to validate the applicability of the JUPITER to the hydraulic relocation behavior in core internals. The test section used in this experiment simulated the structure of the core internals, such as a control rod and a fuel support piece, simply. The working fluid is water under the atmospheric pressure. The experiment uses a high-speed video camera to visualize the flow behavior. The behavior and the speed of the liquid film in a narrow flow channel is obtained. For the numerical analysis carried out prior to the experiment, the behavior of flow down liquid was shown. The typical behavior was also observed that the tip of a liquid film flowing down splits into.

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Application of Direct Numerical Simulation to Determine the Correlation Describing Friction Losses during the Transverse Flow of Fluid in Hexagonal Array Pin Bundles

Fluids ◽

10.3390/fluids7010022 ◽

2022 ◽

Vol 7 (1) ◽

pp. 22

Author(s):

Yury Shvetsov ◽

Yury Khomyakov ◽

Mikhail Bayaskhalanov ◽

Regina Dichina

Keyword(s):

Numerical Simulation ◽

Reynolds Number ◽

Pressure Drop ◽

Liquid Metal ◽

Direct Numerical Simulation ◽

Incompressible Fluid ◽

Reactor Core ◽

Transverse Flow ◽

Hexagonal Array ◽

Flow Through

This paper presents the results of a numerical simulation to determine the hydraulic resistance for a transverse flow through the bundle of hexagonal rods. The calculations were carried out using the precision CFD code CONV-3D, intended for direct numerical simulation of the flow of an incompressible fluid (DNS-approximation) in the parts of fast reactors cooled by liquid metal. The obtained dependencies of the pressure drop and the coefficient of anisotropy of friction on the Reynolds number can be used in the thermal-hydraulic codes that require modeling of the flow in similar structures and, in particular, in the inter-wrapper space of the reactor core.

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Void Reactivity Effect Research on Liquid Metal Cooled Fast Reactor

Volume 5: Advanced and Next Generation Reactors, Fusion Technology; Codes, Standards, Conformity Assessment, Licensing, and Regulatory Issues ◽

10.1115/icone25-67368 ◽

2017 ◽

Author(s):

Yang Lyu ◽

Xiao Liang

Keyword(s):

Liquid Metal ◽

Power Systems ◽

Fast Reactor ◽

Nuclear Power ◽

Reactor Core ◽

Nuclear Industry ◽

Fourth Generation ◽

Reactivity Effect ◽

The Core ◽

Reactivity Coefficient

In the fourth generation of advanced nuclear power systems, the liquid metal cooled fast reactor plays a more and more important role, such as SFR, LFR and ADS system with LBE coolant. Void reactivity effect means bubbles produced in the core area will induce the change of reactivity. And this reactivity will affect the safety of the reactor. Through investigation and comparison of several liquid metal cooled fast reactors in the nuclear industry, this paper studies bubbles in different positions and partial voiding of the active zone inside the core and fuel assemblies with Monte Carlo core physics calculation method and then concludes the main influencing factors of void reactivity coefficient. The results can provide reference for the follow-up research and development of new type liquid metal fast reactor core design.

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Direct Numerical Simulation of the Flow Through a Structured Pebble Bed Near a Wall Boundary

Volume 1: Symposia ◽

10.1115/ajkfluids2015-3701 ◽

2015 ◽

Cited By ~ 1

Author(s):

Lambert Fick ◽

Elia Merzari ◽

Yassin Hassan

Keyword(s):

Numerical Simulation ◽

Fluid Flow ◽

Direct Numerical Simulation ◽

Flow Behavior ◽

Normal Operation ◽

Fourth Generation ◽

Wall Region ◽

Face Centered Cubic ◽

Flow Data ◽

Pebble Bed

Packed pebble beds occur in many industrial applications, including the very high temperature and molten salt nuclear reactor design concepts. These designs are currently being researched as possible fourth-generation nuclear power system designs. In order to ensure proper cooling of the reactor cores in these systems during normal operation, as well as under accident conditions, a detailed understanding of the coolant flow behavior is required. Direct numerical simulation (DNS) can be used to simulate specific pebble bed flow and geometry conditions in order to develop high-fidelity fluid flow data and hence improve scientists’ understanding and enhance lower-fidelity modeling. We have used Nek5000, a spectral-element computational fluid dynamics code, to develop DNS fluid flow data for pebble bed flow, including budgets for the Reynolds stresses. The geometry is a structured pebble bed with a face-centered cubic packing arrangement. The flow domain features periodic boundaries in both streamwise and spanwise directions except for a single bounding wall parallel to the flow direction. In a fully periodic domain, the flow was found to be asymmetric. In this work we focus on turbulence properties in the near-wall region and their effect on the overall flow behavior. A set of preliminary Reynolds-averaged Navier-Stokes calculations was also performed to investigate the effect of geometric parameters such as the distance of the wall from the first row of pebbles.

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