examples of cfd applications within licensing and ... · boron dilution transients – validation...

TÜV SÜD Industrie Service GmbH Slide 115-06-24

Examples of CFD Applications within Licensing and Supervising Procedure

P. Schöner, T. Thiele, C. Reichel

Contents


• Nuclear regulatory bodies• Overview of CFD projects at TUEV SUED within licensing and supervising procedure• Examples of CFD projects• Conclusion

Nuclear Regulatory Bodies


Federal Office for RadiationProtection (BfS)

Independent authorised technicalexpert organisations, e.g. TÜV

Advisory committees and independentauthorised expert organisations, e. G.:- Reactor Safety Commission (RSK)- Commission on Radiological Protection (SSK)- Nuclear Waste Management Commission (ESK)- Gesellschaft für Anlagen und Reaktorsicherheit (GRS)

Länder CommitteeFor Nuclear Energy

Subordinate Land authorities

Federal oversight ofthe lawfulness andexpediency of theactions of the Länder,federal regulatorydirective in individualcases

Co-operation of federal and Länder governmentswith the aim to developand uniformly applyregulations and toachieve an equal level ofprecaution throughout the federation

Federal Ministry for the Environment, Nature Conservation, Building and Nuclear Safety (BMUB)

Land ministry - responsible forlicensing and supervision of nuclear installations

Quelle: www.bfs.de/de/kerntechnik/sicherheit/Regulatory_body.jpg

CFD Projects – Overview


• Mixing of boron acid in the reactor cooling circuit (boron dilution)• Temperature distribution coupled with heat transfer in reactor coolant line and

reactor pressure vessel; emergency coolant injection; pressurized thermal shock (PTS)

• Flow distribution in the reactor pressure vessel and reactor core (PWR, flow force exerted on the fuel assemblies)

• CFD-Calculation of 2-Phase-Flow Phenomena in the pump bending loop duringloss of coolant accidents (LOCA) in pressurized water reactors (PWR)

• Transport and deposition of insulating material in the reactor core during LOCA (PWR)• Sedimentation of insulating material in pressure suppression pools (BWR)

CFD Projects – Overview


• Temperature distribution in a storage/transport cask for nuclear waste due to fire burden• CASTOR® cooling in temporary storage facilities (natural convection)• Temperature distribution inside a CASTOR® (regular operation within temporary storage

facility)

Special projects:• Calculation of leak flow rates• Optimization of an isolating valve (pressure drop)• Transport of removed impeller cap of RCP during start up operation• Calculation of 3D-pressure waves in case of a pressure vessel failure

Boron Dilution Transients (PWR)


• Use of Boric Acid to keep the core subcritical in certain scenarios (PWR)

• Calculation of minimum permitted Boron concentrationfor each fuel cycle and scenario (e.g. Reflux-Condenser-Mode during SB-LOCA)

• Submission of test (UPTF, ROCOM) and CFD results byoperators to extend duration of fuel cycle => Minimum boron concentration >1400 ppm

• TUEV SUED: Confirmation of minimum boron concentration

Natural convectionECC

Boron Dilution Transients – Validation


Validation by comparing the minimum boron concentration, determined by ROCOM1

experiments and CFD calculations, at certain locations in the RPV

879

615

383

1808

1464

1009

408

1785

1493

1449

1281

546

1686

1291

1058

787

364

1467

1304

1092

780

368

1486

1250

985

498

248

1688

1149

1989

0 500 1000 1500 2000 2500

Kerneintritt

DC unten

DC Mitte 2

DC Mitte 1

DC oben

Minimale Borkonzentration [ppm]

CFX (ROCOM02_b)CFX (PHOENICS)PHOENICSROCOM_02bROCOM_02aROCOM_01

1 Rossendorf Coolant Mixing Model

DC top

DC 1

DC 2

DC bottom

Core inlet

Minimum Boron concentration [ppm]

Boron Dilution Transients – Cold Leg Mixing


Transport of the under-borated slug in the cold leg

Boron Concentration[ppm]

Boron concentration slug: 50 ppm; Boron concentration Pipe: 2500 ppmMass flow: ROCOM_02b

Boron Dilution Transients – Results


• Under-borated slug does not form a plume by itself under given boundary conditions

• Stratification of cold and hot water

• Formation of a cold water plume in the downcomer by ECC injection

• Admixture of the under-borated slug with the cold water plume

• Transport of under-borated slug towards reactor core

• Minimum concentration of boron calculated using ANSYS CFX®

at reactor core inlet 1470 ppmless uncertainty derived from ROCOM tests => 1250 ppm

Pressurized Thermal Shock (PTS)


PTS limits the lifetime of NPPs

Loads on the Reactor Pressure Vessel (RPV)relevant for brittle fracture may arise from • an increase of coolant pressure

• a decrease of coolant temperature or

• a combination of both=> Pressurized Thermal Shock (PTS)

ScenarioInjection of cold emergency core cooling (ECC) water during loss of coolant accidents (LOCA)=> high loads due to intense cool down of

the RPV wall

global p, T, loop and injection mass flow rates

PTS – Workflow


Calculation of the system parameters during accidents(initial and boundary conditions)with 1D-code RELAP5

Mixing analyses: calculation of the local temperature distribution

with 3D-code ANSYS CFX (NPP Owner: KWUMIX)

Fracture mechanics analyses of the Reactor Pressure Vessel

Postulated cracks: nozzle corner, flange joint and core beltline region

global p, local T

PTS ANSYS CFX® – Results


Temperature distribution at 470 sshowing phenomena typical for the time period between pump run down and global cool down of the whole RPV wall: • Temperature stratification in the

loops• One of the oscillating cold water

plumes attached to the RPV wall• One of the oscillating cold water

plumes temporarily detached• Global cool down of the bottom

region

PTS Validation – UPTF


Measurement Position JEC02CT041-46 (Stalk 4)

60,000

80,000

100,000

120,000

140,000

160,000

180,000

200,000

0,000 50,000 100,000 150,000 200,000 250,000 300,000 350,000 400,000 450,000 500,000

time t [s]

fluid

tem

pera

ture

TF

[°C

]

SST-JEC02CT041 SST-JEC02CT042 SST-JEC02CT043 SST-JEC02CT044 SST-JEC02CT045 SST-JEC02CT046

exp-JEC02CT041 exp-JEC02CT042 exp-JEC02CT043 exp-JEC02CT044 exp-JEC02CT045 exp-JEC02CT046

SAS-JEC02CT041 SAS-JEC02CT042 SAS-JEC02CT043 SAS-JEC02CT044 SAS-JEC02CT045 SAS-JEC02CT046

PTS Validation – UPTF


PTS (Theofanous-Criterion)


Horizontal pipe; DiameterRCS = 750 mm; DiameterECC = 220 mm; Loop-Temperature: 292°C;ECC-Temperature 15°C; MassflowLoop = 500 kg/s; MassflowECC = 10 kg/s

RPV-Inlet

Change of loop flow due to pump coast-down Flow-Phase (0 s – 400 s): well mixedStagnation-Phase (> 400 s): stratification

ECC

PTS – Results


Flow phase (duration)• Duration adjusted due to results of CFD-simulation

Stagnation phase• SST-turbulence model “conservativ” (RPV touched by plume, stratification in the loop)• KWUMIX confirmed• Results using SAS-turbulence model agree very well with experimental data

Flow Distribution in RPV and Core


Prevent fuel element lift-off due to hydraulic loads=> Determination of flow forces on fuel elements

during permitting procedure for a new type offuel elementsimple approach; uniform flow distribution

Non-uniform flow distribution at the core inlet=> “Inhomogeneous factor” e. g. 14% on flow forcesNew analyzes by owner yielded a value of 9,6% + 4% (non-uniform flow at the core outlet)=> 14% still valid

TUEV SUED: Determination respectively confirmation ofthe “Inhomogeneous factor”

Flow Distribution in Core


Rel. F

uel M

assfl

ow[]

Elevation [m]Inlet Outlet

Flow Distribution - Results


• Even out of flow already in the first half of the reactor core

• Relocation of the remaining flow peak in the upper half of the core from the centre to the edge region

• Effect of RPV outflow on flow distribution in the core non negligible

• Maximum deviation from mean value flow force of about 7 %=> Significant lower than „inhomogeneous factor“ of 14%

Transport/Sedimentation of Insulating Material


Task• Insulation debris released during a LOCA

=> Clogging of fuel elements and sump strainer• Calculation of sedimentation rate e. g. in the pressure suppression pool (BWR) to check results of

NPP owner derived by TISA code

ANSYS CFX® Model• Eulerian-Eulerian-approach (Water and particles as separate inter-penetrating fluids)• Use of three types of particles with different properties• Model parameters based on experimental data for settling velocities• Consideration of turbulent dispersion using turbulent dispersion forces• „Interaction of particles” considered by increasing viscosity with increasing concentration of

particles

Transport/Sedimentation of Insulating Material


Sedimentation in a pressure suppression pool (BWR)

Transport/Sedimentation - Results


• Sedimentation > 60% for scenarios with 1 of 3 ECC-pumps running

• High flow velocities in pressure suppression pool for scenarios with 3 ECC-pumps running=> re-suspension

• ANSYS CFX® results show low sedimentation rate (~30%)=> TISA results not confirmed

CASTOR® Cooling in Interim Storage Facility


Determine the influence of cask position on the cask surface temperature

Boundary ConditionsInlet temperature: 29 °CDecay heat of grouped storage casks: 11 kW - 30 kW; Decay heat of “single“ storage casks: 35 kW

Positioning 1 Positioning 2

CASTOR® Cooling - Results


Positioning 1 Positioning 2

Increase in the average surface temperature (“hottest CASTOR®”) of 9,6 K for positioning 2

Optimization of an Isolating Valve


0,0

10,0

20,0

30,0

40,0

50,0

60,0

70,0

80,0

90,0

0 0,01 0,02 0,03 0,04 0,05 0,06 0,07 0,08 0,09 0,1 0,11 0,12

Druckverlust [bar]

Ventilhub [m]

optimiertes Ventil

as built Ventil

OpenFoam

Valve Lift [m]

Pres

sure

Dro

p [ba

r]

Optimized Valve

As Build Valve

CFD

Check valve characteristics of a main steam relief isolation valve

OpenFOAM mesh: Snappy HexMesh 800.000 cellsBoundary conditions:Fluid: Saturated SteamPressure: 85,0 barTemperature: 300,0 °CVelocity at inlet: 10 m/s

Calculation of 3D-pressure waves


Determination of dynamic blast loading on buildings due to pressure vessel burst

Operator: ANSYS LS-DYNA®

TUEV SUED: ANSYS CFX® and OpenFOAM®

3D Pressure Waves – Results


Time [s]

Abs.

pres

sure

[Pa]

Loads on exhaust stack

Transport of detached Impeller Cap


Initial and boundary conditions

Temperature: 280 °CPressure: 140 barMass flow: 2200 kg/s(3-loop-mode => back flow)

Impeller capDiameter: 150 mmDrag coefficient: 1,34Density: 7800 kg/m³

ANSYS CFX®Particle tracking

Transport of Impeller Cap - Results


Conclusion


• CFD is often the only alternative calculation technique

• CFD application leads to the detection of physical phenomena and to the identification of error sources

• Initial assessment with little effort

• Accuracy increases with effort

• CFD will not replace experiments completely

• CFD is indispensable within licensing and supervising procedure

examples of cfd applications within licensing and ... · boron dilution transients – validation...

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