DiFis 2'0 3D Finite Element Neutron Kinetic Code

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DiFis 2.0 3D Finite Element Neutron Kinetic
Code
17th AER Symposium on VVER Reactor Physics and
Reactor Safety

• A.I. Zhukov and A.M. Abdullayev
• NSC Kharkov Institute of Physics and Technology
• September 24 - 28, 2007 Yalta, Ukraine

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Objective

• Existing 1D kinetic codes too conservative
• SNRCU intend to require 3D analysis for accidents
  with reactivity insertion (Control Rod Eject
  Accident and others)

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Background

• Westinghouse PHOENIX-H code (XS)
• Westinghouse Advanced Nodal Code (ANC-H)
• Westinghouse 1D-3D neutron kinetic code TWINKLE
  (for PWR square FA lattice)
• DiFis 1.0 3D FE steady-state code
• FE methodology

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Nuclear Model
2 group approximation

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Thermal Hydraulic Model
Average Fuel Rod (one per assembly)

for fuel, gap, cladding
for coolant
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Feedback Models

• PHOENIX-H provides all XS with feedback
• Moderator density correction includes
• Diffusion coefficient correction
• Moderator absorption correction
• Boron concentration correction
• Spectrum correction
• Fuel temperature correction
• Xe, Sm, Pm correction
• Control Rod correction

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Finite Element Technique - 1

Expansion of fluxes into series over linear
functions
Set of simplex-functions
Set of linear functions
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Finite Element Technique - 2

Weighted Residual Equations
or
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Finite Element Technique - 3

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Finite Element Technique - 4

Fuel Rod Normally Fuel 7 zones Gap 2
zones Clad 5 zones Axial 24 zones
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Code capabilities

• Core Power vs. time
• Spatial and time power distribution
• Spatial and time temperature distribution in
  fuel, cladding and coolant

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Example of Steady-State Calculations

EOC Relative FA Power ANC DiFis-ANC
Max Err 4.0 Rms Err 1.6
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Example of Transient Calculations - 1

Control Rod Eject Accident
Timeline
start finish all banks start
to drop
finish
0 s 0.1 s 0.4 s

3.0 s
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Example of Transient Calculations - 2
Rod Cluster Worth 0.18

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Example of Transient Calculations - 3

Doppler only FA under ejected RCCA
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Example of Transient Calculations - 4

All Banks drop FA under ejected RCCA
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Example of Transient Calculations - 5

Doppler only FA under ejected RCCA
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Example of Transient Calculations - 6

All Banks drop FA under ejected RCCA
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Summary

• DiFis 2.0 compatible with well-known codes such
  as PHOENIX-H and ANC-H
• DiFis 2.0 provides accuracy 4 (in compare with
  ANC) for steady-state calculations
• DiFis 2.0 justification and benchmarking to be
  continued