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DYN3D/ATHLET AND ANSYS CFX CALCULATIONS OF THE OECD VVER-1000 COOLANT TRANSIENT BENCHMARK. S. Kliem , T. Höhne, U. Rohde Forschungszentrum Dresden-Rossendorf Institute of Safety Research Y. Kozmenkov IPPE Obninsk. “Assurance of NPP with WWER” Podolsk, 29 May-1 June, 2007. Introduction (1). - PowerPoint PPT Presentation
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Institute of Safety Research
Member Institution of the Scientific Association Gottfried Wilhelm Leibniz
DYN3D/ATHLET AND ANSYS CFX CALCULATIONS OF THE OECD VVER-1000
COOLANT TRANSIENT BENCHMARK
S. Kliem, T. Höhne, U. RohdeForschungszentrum Dresden-Rossendorf
Institute of Safety Research
Y. KozmenkovIPPE Obninsk
“Assurance of NPP with WWER”Podolsk, 29 May-1 June, 2007
Institute of Safety Research
Member Institution of the Scientific Association Gottfried Wilhelm Leibniz
Introduction (1)
• OECD/NEA Benchmark for VVER-1000
• 2 Phases
– Calculation of a start-up experiment “Switch-on of one main coolant pump while the other three are in operation”
– Calculation of coolant mixing experiments at low reactor power (isolation of one steam generator at running pumps)
• Reference plant: NPP Kozloduy-6 (Bulgaria)
Institute of Safety Research
Member Institution of the Scientific Association Gottfried Wilhelm Leibniz
Introduction (2)
• Our institute is taking part in the calculations of the benchmark
• Phase 1: coupled neutron kinetic/thermal hydraulic system code DYN3D/ATHLET
• Phase 2: commercial computational fluid dynamics code ANSYS CFX
Institute of Safety Research
Member Institution of the Scientific Association Gottfried Wilhelm Leibniz
• DYN3D– Excellent validation
basis for hexagonal and square FA geometry
DYN3D3D Core Model
Steady State and TransientCartesian and Hexagonal
Geometry
NeutronKinetics
ThermalHydraulics
2 - neutron groupsdiffusion theory
3 - dimensionalnodal methodsversions for
quadratic assemblieshexagonal assemblies
1D 4-equations th. modelfor two phase flowradial heat conductionin fuel and cladheat transfer modelssafety parametersboron mixing models
calculation of cross sections
nodal powers
fuel temperaturescoolant densitiescoolant temperaturesboron concentrations
library of group constantsburnup distribution
cross sections of nodes
Institute of Safety Research
Member Institution of the Scientific Association Gottfried Wilhelm Leibniz
DYN3D/ATHLET
• Coupling
Institute of Safety Research
Member Institution of the Scientific Association Gottfried Wilhelm Leibniz
Phase 1
• Core and loop positions
Loop to be switched on
Institute of Safety Research
Member Institution of the Scientific Association Gottfried Wilhelm Leibniz
Phase 1
• Velocity in the loops (cold leg)
Institute of Safety Research
Member Institution of the Scientific Association Gottfried Wilhelm Leibniz
Phase 1
• Temperatures in the loops (cold leg)
Institute of Safety Research
Member Institution of the Scientific Association Gottfried Wilhelm Leibniz
Problem
• Initial state: three active loops• Final state: four active loops• Open: How to model the transition inside the
system code • The old question:
Institute of Safety Research
Member Institution of the Scientific Association Gottfried Wilhelm Leibniz
Lower plenum
Simplified empirical mixing modelAssumptions
– Inside the pressure vessel, there is an azimuthal equalisation of the flow rates from the single loops.
– The flow shifts from the loop position to the sector position.
– The redistribution of the flow of all active loops results in a zero net shift.
– The described sector formation is present in the vessel until the core inlet plane.
Implementation– Recalculation of the positions of the sectors and
the FA belonging to the single sectors
Institute of Safety Research
Member Institution of the Scientific Association Gottfried Wilhelm Leibniz
Upper plenum
• Upper plenum nodalization at the elevation of the hot leg nozzles
H o t leg n o zz le # 3
Ju n c tio n 2 Ju n c tio n 1
F ro m the co re o u tle t
A B H o t leg n o zz le # 2
H o t leg n o zz le # 4
H o t leg n o zz le # 1
C
Institute of Safety Research
Member Institution of the Scientific Association Gottfried Wilhelm Leibniz
Validation of lower plenum mixing model
• No experiments but CFD• A model of the vessel was developed and used for Phase 2
(stationary mixing experiment)• One transient calculation
– modelling of the transport of a perturbation (e.g. temperature)
– four passive scalars (one for each loop at the inlet positions into the vessel) of infinite length
– transported with the fluid and are subject of turbulent dispersion, but do not affect the flow field
– Individual transport equation for each scalar– Result: time and space dependent contributions of the
flow of all loops to the distribution of the perturbation at each fuel element position in the core inlet plane
Institute of Safety Research
Member Institution of the Scientific Association Gottfried Wilhelm Leibniz
Model of the VVER-1000 reactor
An exact representation of the inlet region, the downcomer below the inlet region, the 8 spacer elements in the downcomer and the lower plenum structures is necessary
The mesh contained 4.7 Mio. tetrahedral elements (IC4C)
CFX-5 Grid
Institute of Safety Research
Member Institution of the Scientific Association Gottfried Wilhelm Leibniz
Modeling the Porous Regions
1
2
Porous Regions:
(1) Elliptical Sieve Plate
(2) Perforation region of support tubes
Elliptical sieve plate
Support columns
Perforated columns
The Lower Plenum structure– Elliptical perforated core
barrel plate – 163 partly perforated
support columns– Each column is associated
to a fuel assembly
Institute of Safety Research
Member Institution of the Scientific Association Gottfried Wilhelm Leibniz
Validation of lower plenum mixing model
Velocity in the loops
Institute of Safety Research
Member Institution of the Scientific Association Gottfried Wilhelm Leibniz
Phase 1 – Initial state
Parameter Measured data Accuracy DYN3D/ATHLET
Keff - - 0.999200
Core power, MW 824 ±60 MW 823.85
Upper Plenum pressure, MPa
15.6 ±0.3 MPa 15.606
Temperature CL1, K 555.6 ±2.0 K 554.83
Temperature CL2, K 554.6 ±2.0 K 553.50
Temperature CL3, K 554.4 ±2.0 K 554.42
Temperature CL4, K 555.3 ±2.0 K 554.93
Temperature HL1, K 567.1 ±2.0 K 566.06
Temperature HL2, K 562.1 ±2.0 K 560.96
Temperature HL3, K 550.8 ±2.0 K 550.53
Temperature HL4, K 566.2 ±2.0 K 566.06
Institute of Safety Research
Member Institution of the Scientific Association Gottfried Wilhelm Leibniz
Phase 1: Transient
• Measured and calculated upper plenum pressure
Institute of Safety Research
Member Institution of the Scientific Association Gottfried Wilhelm Leibniz
Phase 1: Transient
• Measured and calculated coolant temperatures in loop 3
Institute of Safety Research
Member Institution of the Scientific Association Gottfried Wilhelm Leibniz
Phase 1
• Calculated normalized fuel assembly power values
greatest changes
Institute of Safety Research
Member Institution of the Scientific Association Gottfried Wilhelm Leibniz
Phase 2
• Available data– Stationary temperature distribution at the core inlet
– Derived during recalculation from core outlet measurements under some assumptions
• Peculiarity– Non-symmetrical connection of the loops on the
vessel
Institute of Safety Research
Member Institution of the Scientific Association Gottfried Wilhelm Leibniz
Phase 2
• Relative core inlet temperatures
Institute of Safety Research
Member Institution of the Scientific Association Gottfried Wilhelm Leibniz
Phase 2
• Steady state results using three different turbulence models– Shear stress turbulence
– Largy eddy simulation
– Detached eddy simulation
Institute of Safety Research
Member Institution of the Scientific Association Gottfried Wilhelm Leibniz
Phase 2
• Deviations between DES-calculation and measurement
DEV(i)=CFD(i)-EXP(i)
Institute of Safety Research
Member Institution of the Scientific Association Gottfried Wilhelm Leibniz
Conclusions
• Calculation of both phases of the VVER-1000 Coolant
transient benchmark
• Phase 1: DYN3D/ATHLET calculation
– Use of a simplified mixing model at the interface between
system code and core model
– proof of the applicability by comparison with a transient
CFD calculation using ANSYS CFX• Phase 2: ANSYS CFX calculation
– Good agreement in temperature distribution – Small changes during the variation of the turbulence
models