wir schaffen wissen – heute für morgen a. dehbi, d. suckow, t. lind, s. guentay paul scherrer...

Wir schaffen Wissen – heute für morgen

A. Dehbi, D. Suckow, T. Lind, S. GuentayPaul Scherrer Institut, Switzerland

Large Scale Experimental Program at PSI on Safety Issues in a PWR Steam Generator

ERMSAR2012, Cologne, Germany, March 21-23, 2012

Nuclear Energy and SafetyLaboratory for Thermal Hydraulics

Severe Accident Research Group, SACRE

ERMSAR2012, March 21-22, 2012 PSI, 21.04.23, 2

Project Overview – International collaboration project Steam condensation / Reflux condensation

• Background• Objectives of the Reflux Project• Reflux Single Tube Test Facility• Reflux Test Plan

Steam Generator Mixing and Recirculation under SBO initiated Severe Accident Conditions

• Background• System code approach• CFD Simulation• Facility Scaling• Test Facility and Experimental Program

Summary

Presentation Outline



ERMSAR2012, March 21-22, 2012 PSI, 21.04.23, 3

1) Steam / Reflux condensation, DBA and BDBA: Amount of coolant available for core cooling Timing and efficiency of EOP and SAM measures• To Improve system codes and bench-mark CFD

- In the presence of non-condensable gases- In the presence of aerosols- At high pressures (20 -100 bar)

2) Mixing and recirculation in the steam generator during PWR severe accidents:

Thermal challenge to primary pressure boundary Failure of the components Source term• To scale-up of the methodology and bench-mark CFD• 1/7 scale facility with improved scaling and instrumentation• The effect of the steam generator design (geometry)

Two Part Project Overview



ERMSAR2012, March 21-22, 2012 PSI, 21.04.23, 4

Reflux condensation: Background (1)

o Reflux condensation removes residual decay heat under conditions with:• reduced primary side water inventory• secondary side heat sink• LOCA, mid-loop operation

o Condensate flows counter-current to steam• Steam generated due to decay heat• Condensation in the steam generator• Condensate flows back into core• Different modes of operation: film-wise,

oscillatory, carry-overFrom RV

To RV

U

Xg

T

Wall

Condensate Mixture of Steam,NC-Gas

Hot Leg

SG Tubes

SG secondary side

Outlet Plenum

Inlet Plenum Condensate

Mixture of Steam,NC-Gas



ERMSAR2012, March 21-22, 2012 PSI, 21.04.23, 5

• Pure steam condenses efficiently• Efficiency decreased by:

• Non-condensable (NC) gases - N2 from accumulator injection- Air migration during mid-loop operation- H2 from fuel (severe accident)• Aerosols (severe accident)

Heat transfer and steam condensation during counter / co-current flow• at high pressures (5-100bar)• for high content of non-condensable gases N2

and He (H2)• under co-current and counter current flow

conditions => CCFL• in laminar to turbulent flow regimes• in the presence of aerosols

Reflux condensation: Objectives

Aerosol deposition

super-heated steam and NC gas

Aerosols

Condensation under influences of NC gasand aerosols

Degrading

Boiling cross over leg(loop seal)

cold leg

hot leg

surg

e lin

e

Pre

ssur

izer

SG outletplenum

SG inletplenum

SG secondary side

U-tube bundle

Steam Generator SG

Reactorvessel

Hot legbend

Aerosol deposition

super-heated steam and NC gas

Aerosols

Condensation under influences of NC gasand aerosols

Degrading

Boiling cross over leg(loop seal)

cold leg

hot leg

surg

e lin

e

Pre

ssur

izer

SG outletplenum

SG inletplenum

SG secondary side

U-tube bundle

Steam Generator SG

Reactorvessel

Hot legbend



ERMSAR2012, March 21-22, 2012 PSI, 21.04.23, 6

TRACE Condensation Model: Status*

*A. Manera, CAMP Meeting, Nov. 2007

Film Condensation without NC Gases•Very good agreement for condensation without NC for large pressure range•Improvements needed for very low pressure and low liquid film Reynolds numbers

Film Condensation with NC Gases•Default model of TRACE code very approximate•Significant improvements with TRACE advanced condensation model•Further developments still needed for:•High content of NC (20-90%)•High pressures (20-100 bar)



ERMSAR2012, March 21-22, 2012 PSI, 21.04.23, 7

RFLX Single Tube Facility

Tube 1: 45 x 20 mm Tube 2: 19.05 x 16.8 mm Length 4.5 m Material SS 316L

Steam: up to 25 kg/h NC: N2 0-91 w-%

He: 0-45 w-%

Primary: 1.5 -100 bar 400°C Secondary: 1 - 80 bar 35 – 295°C

saturatedor subcooledwater cooling

MM

He

N2

SteamGenerator

SuperHeater

Mixer

Heater

HX

Flowrate

Condensate

HXM

M

M

CondensateSeparator

Non-Condensables

dem.Water

SeparatorDrum

Condenser/Pressurizer

PrimaryLoop

HeaterCirculationPump

SecondaryLoop

4.5

m

el.

HX

Heater

FlowRate

SprayPump

upperplenum

lowerplenum

M

HX

Flowrate

Flowrate

Flowrate

ø 45 x 20

ø 114.3

(ø 19.05 x 16.8)



ERMSAR2012, March 21-22, 2012 PSI, 21.04.23, 8

RFLX Test matrix

Test matrix comprised of 5 Phases and 50 Tests

Configuration Characteristics, Variations

I Reflux mode, pure steam condensation NC mass fraction: 0%Primary total pressure: 2 - 95 barInjection from bottom / top

II Reflux mode, steam + noncondensable (NC) NC mass fraction: 1% - 91%Primary total pressure: 2 - 95 bar

III Once-through counter-current mode (NC) NC mass fraction: 1% - 91% Primary total pressure: 2 - 95 barup to CCFL point

IV Once-through co-current mode NC mass fraction: 1% – 91%Primary total pressure: 2 - 95 barCCFL onwards to flooding, spill-over

V Open tests To be assigned



ERMSAR2012, March 21-22, 2012 PSI, 21.04.23, 9

Steam Generator Mixing: Background

o SBO severe accident sequence• Hot leg voided by venting coolant through

pressurizer• Cold leg loop seal plugged with water• Primary: high pressure; Secondary: dry,

depressurized (“high, dry, low”)o Hotleg counter-current natural circulation

• Transfer heat to hot leg, surge line and SG tubes• Hot flow counter-current to cold flow• Mixing of hot and cold gas in inlet plenum• Flow recirculation through SG U-tubes Thermal challenge to surge line and SG tubes Source term



ERMSAR2012, March 21-22, 2012 PSI, 21.04.23, 10

Mixing: System Code Approach

o MELCOR 1.8.5: Pairs of flow paths to simulate counter-current and inlet plenum mixing

o Required inputs:• Recirculation ratio: flow rate in tubes/flow rate in hotleg

• Fraction of tubes which receive hot fluid (flow upwards)

→ To predict the actual response and mixing parameters requires experimentally validated CFD

o SOARCA by US NRC (NUREG-1935, 2012):• Limited data available, only average behaviour• Dependence on geometry, data available for only

one geometry => validity for other geometries?



ERMSAR2012, March 21-22, 2012 PSI, 21.04.23, 11

Facility Scaling: Dimensionless Numbers

360

600

7400

35500

PSI

270

670

8200

170000

PWR

350

210

9200

46500

WG 1/7Parameter

360

600

7400

35500

PSI

270

670

8200

170000

PWR

350

210

9200

46500

WG 1/7Parameter

h

eqHLhHL

DU

Re

otubes

tubestube A

Hm

Re

2Retube

tubetube

GrRi

2

__ ReHL

BundleSGBundleSGHL

GrRi

o Westinghouse (1990) tests to experimentally investigate natural circulation flows during severe accidents in PWRs; limitations on data application: scaling (not conservative), data proprietary

Improved scaling: increased height and number of tubes, reduced tube diameter increased resistance increased Ritube

Improved instrumentation



ERMSAR2012, March 21-22, 2012 PSI, 21.04.23, 12

Schematic of the SG Mixing Facility

Program will produce CFD-grade data: high spatial / temporal resolution of flow fieldo PIV (2 components of velocity and RMS)o Two component LDA:

• Velocity profiles (mean & RMS)• Reynolds stresses, thermal stresses

o Thermocouples (tubes), and thermocouple meshes (hot leg, inlet / outlet plenum)

RPV

Hot leg

Steamgenerator

Leakageexpansion

volumeC

ompr

esso

r

HeatingHeating

SecondaryAir cooling

Surgeline

Parameter Value

Hot leg length (m) 1.2

Hot leg diameter (mm) 83.7

Number of U-tubes 262

Inner Diameter of tubes (mm) 5.0

Tube height (straight) (m) 2.2

SG bundle radius (m) 0.235



ERMSAR2012, March 21-22, 2012 PSI, 21.04.23, 13

Experimental Program

1. Base case: circulation and mixing under “high-dry-low” scenario2. Effect of light gas: He

• Concern: presence of light gas, under low driving ΔT, could lead to stratification and impairment/disruption of counter-current flow (no data available)

3. Leakage: effect of tube leakage on mixing• Leakage will progressively disrupt counter-current flow no data available on the

dynamics of this effect4. Geometry of inlet plenum

• CFD indicates large variations in recirculation ratio no experimental data available with different inlet plenum geometries

NPP Mixing factorFraction hot

tubes

West. 2.7 50 %

CE 1.5 42 %

Boyd: Geometry effect, base case



ERMSAR2012, March 21-22, 2012 PSI, 21.04.23, 14

Summary

The Reflux tests will:• Extend available data base to improve system codes and bench-mark CFD

• In the presence of non-condensable gases• In the presence of aerosols• At high pressures (20-100 bar)

Amount of coolant available for core cooling Better evaluation of accident prgress Timing and efficiency of EOP and SAM measures

The Mixing tests will:• Provide critical mixing parameters (not constant )

• Improved scaling• Effect of different geometries• Light gas• Effect of tube breach

Help protect pressure boundary by better informed accident management Better assessment of the source term



ERMSAR2012, March 21-22, 2012 PSI, 21.04.23, 15

Thank you for your attention



ERMSAR2012, March 21-22, 2012 PSI, 21.04.23, 16

RFLX Facility, Measurements

• Local heat flux → set of thermocouples→ thin-foil heat flux sensors

• Condensate film → flush-mounted pin and wire-wire electrode conductance probes• Condensate flow → Coriolis mass flow meters• Pressure → differential pressure transducers

t

Tw

To

Ti

Tc

Thin-FoilHeat FluxSensor

ThermocouplesHeat FluxMeasurement

Tb

Conductance Pin Electrodes

Condensate FilmMeasurement

Parallel WireConductance Probe



ERMSAR2012, March 21-22, 2012 PSI, 21.04.23, 17

CFD Simulations of Mixing

o At NRC, C. Boyd: 1/7 Westinghouse and full-scale• “A challenge … the extension of a limited set of available test data at 1/7th

scale to the full scale conditions”o At PSI, A. Dehbi: 1/7 Westinghouse

• Flow turbulent and erratic, hot plume wanders around High resolution temporal and spatial data required to benchmark codes

MeanInstan. t=1190 s Instan. t=1210 s

wir schaffen wissen – heute für morgen a. dehbi, d. suckow, t. lind, s. guentay paul scherrer...

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