A Large-Scale Parallel Computing of Boiling Two-Phase Flow Behavior in Advanced Light-Water Reactors

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A Large-Scale Parallel Computing of Boiling
Two-Phase Flow Behavior in Advanced Light-Water
Reactors

• K. Takase, H. Yoshida, T. Misawa
• Thermal Fluid Engineering Group
• Japan Atomic Energy Agency

VECPAR 2008 Toulouse, France, 24-27, June 2008
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Objectives

• To establish a new thermal design procedure of
  nuclear reactors with large-scale numerical
  simulations
• To attain the design by analysis
• To simulate precisely two-phase flow
  characteristics in fuel bundles and,
• To clarify physical mechanisms on boiling
  transition, two-phase turbulent structure, etc.

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Developed Analysis Code

• The code is discretized by the CIP method
  (Yabe, 1993).
• Analyze 3-dimensional compressible/non- compressi
  ble flows.
• Consider CSF model (Brackbill,1992) as
  calculation of surface tension
• The interface tracking method (Youngs,1982) was
  modified for predicting a water-vapor interface.
• As a matrix solver, the AMG method was applied.
  The code was parallelized by MPI and Open MP.

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Basic Equations
Basic equations of the time-dependent mass,
Navier-Stokes, energy, etc. for compressible flow
are as follows.

• Mass
• Density

• Momentum
• Volume fraction
• Energy

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Used Supercomputers

• ? Earth Simulator (JAMSTEC)?
• Vector parallel computer
• 640 nodes, 8 CPU/node, 5120 CPU, 10 TB, 40
  TFlops.
• ? Altix 3700 Bx2 (JAEA)
• Scalar parallel computer 16 nodes, 128
  CPU/node, 2048 CPU, 13 TB, 13 TFlops.

Earth Simulator
Altix 3700 Bx2
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37-Rod Bundle Configuration

• The present analytical geometry, a 37-rod bundle,
  simulates the RMWR core condition and the
  experimental condition
• Hexagonal flow passage
• Inlet section 100 water
• Outlet section 90 Vapor
• 13 mm in rod diameter
• 1.3 mm in gap spacing and,
• Four grid spacers in axially.

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Computational Grid
Average grid size (0.1 mm)?
Fuel rod
Grid spacer
Fluid
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Analytical Conditions

• Inlet condition
• Temperature 288oC, pressure 7.2 MPa, flow rate
  400 kg/m2s, and the estimated Reynolds number is
  40,000.
• Boundary conditions
• No-slip condition on every wall
• Velocity profile is uniform at the inlet section
• Inlet velocity is set to 0.5 m/s.

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• Simulated Liquid Film Flow

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Predicted Axial Velocities
Outlet
Spacer No.4
Spacer No.3
Behind spacer
Just spacer
Spacer No.2
Spacer No.1
Velocity (m/s)?
18
9
0
In front of spacer
Inlet
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Liquid Film Flow on Fuel Rods
Spacer position
Interface behavior between liquid and gas
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Predicted liquid film flow
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Comparison of Predicted and Experimental Results
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0.5
0
Void fraction
(100 water)?
(100 vapor)?
Fuel rod
Fuel rod
Predicted result
Experimental result by neutron radiography
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• Simulated Bubbly Flow

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Photo-Realistic Visualization by the Ray
Tracing Method
By Ray Tracing
By AVS
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• Simulated Boiling Configuration

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Predicted Water-Vapor Configuration
Outlet
Flow direction
Inlet
Predicted result Experimental result
Fuel bundle
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Conclusions

• Two-phase flow characteristics on liquid film and
  bubbly flow were predicted by a newly developed
  analysis code
• When a large-scale simulation is carried out
  under the simulated reactor core geometry, high
  performance parallelization approach is the most
  important key technology
• The high prospect was acquired on the possibility
  of establishment of the thermal design procedure
  of nuclear reactors with numerical simulations
  and,
• Furthermore code validation will be continued.

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END