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Department of
Nuclear Engineering
& Radiation Health Physics
Phenomena 13: Behavior of Emergency HeatExchangers and Isolation Condensers
4th Research Coordination Meeting of the IAEA
CRP on Natural Circulation Phenomena, Modeling and Reliability ofPassive Systems that Utilize Natural Circulation
Brian G. WoodsK. Nelson
Jose N. Reyes, Jr.
September 10-13, 2007
IAEA, Vienna, Austria
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Department of
Nuclear Engineering
& Radiation Health Physics
Outline Description of Emergency Heat
Exchangers
PRHR Phenomena
APEX Test Data
Description of Isolation Condenser
IC Phenomena Experiments
Correlations
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Passive Residual Heat Removal (PRHR)
System
The PRHR is a type ofEmergency HeatExchanger
Closed loop that providesa flow path from the
reactor to a heatexchanger immersed in alarge tank of water.
PRHR operates at fullsystem pressure withsingle-phase liquid natural
circulation Provides decay heat
removal during stationblackout.
REACTOR
VESSELCOOLING
TANK
PRHR HEAT
EXCHANGER
NORMALLY
CLOSED
NORMALLY
OPEN
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Emergency Heat Exchanger Phenomena
The following phenomena are important toPRHR performance and reliability: *Buoyancy Force
*Emergency Heat Exchanger Loop FlowResistance
*Single-phase Convective Heat Transfer
Shell-Side Nucleate Boiling Heat Transfer
*These phenomena are relatively wellunderstood for single phase fluid flow. See
IAEA-TECDOC-1474.
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PRHR Experiments In APEX Test Facility
Series of forced flow and natural circulationtests conducted at OSU in the APEX facilityfor AP600 certification.
NRC-2 simulated a a loss of all AC powerto all reactor systems.
Decay heat was removed by the PassiveResidual Heat Removal System using theC-Type PRHR Heat Exchanger immersed
in the IRWST. 88 Stainless Steel Tubes
The test duration was ~24,000 seconds.
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Passive Residual Heat Removal (PRHR) System
(Description of Flow Path)
Actuates on Low PZR Pressure or Level
Station Blackout
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IRWST PRHR Heat Exchanger
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Fluid Temperature Measurements in IRWST
and PRHR Tubes
TF-711
TF-710
TF-709
TF-708
TF-707
TF-706
TF-705
TF-704
TF-703
TF-702
TF-701
ZONE 4
ZONE 3
ZONE 2
ZONE 1
TF- 810
TF- 811
TF- 808TF- 809
TF- 805
TF- 806
IRWST PRHR Hx
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NRC-2 IRWST Thermal Stratification
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Fraction of Heat Load Transferred in Each Zone (NRC-2)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
2000 4000 6000 8000 10000 12000 14000 16000 18000
Time (s)
Fraction
ofHea
tLoad
Zone 1 Zone 2
Zone 3 Zone 4
Top Horizontal Bundle
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Test Results
Significant thermal stratification was observed in theIRWST during the Station Blackout Test (NRC-2)
A saturated layer forms at the top of the IRWST as the result of
a thermal plume rising from the PRHR heat exchanger.
The data Indicates that the top horizontal bundle in the
PRHR (Zone 1) serves to transfer a major portion of
the heat load throughout the transient.
As the saturation layer grows, the top zone becomes
less effective and Zones 2 and 3 become more
effective.
Recirculation patterns were observed at the free
surface of the IRWST.
Limited results were published in NUREG/CR-6641
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PRHR Overall Heat Transfer Coefficients
PRHR Heat Exchangeroverall heat coefficient, Uwas determined for a seriesof forced flow and naturalcirculation tests using thelog-mean temperaturedifference.
Forced flow inside the tubesresulted in U = ~450 W/(m2-K) for a wide range of corepowers.
Natural Circulation resultsvaried from U = ~450 to 1100W/(m2-K) over a similarrange of core powers.
Found to be an effectivemeans of decay heat removal
LM
qU
T
, ,,
,
Hx in IRWST Hx out IRWST
LM
Hx in IRWST
Hx out IRWST
T T T T T
T TLn
T T
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Isolation Condensers
Typically used in BWRsto remove core decayheat in the event ofreactor isolation
Heat is transferred fromthe steam through theemergency heatexchanger tubes into thepool by threemechanisms; Two-phase convective
heat transfer andcondensation at thetube inside surface,
Heat conductionthrough the tube walls,
Convective heat transferat the tube outsidesurface.
COOLING
TANK
BWR
VESSEL
IC HEAT
EXCHANGER
MAIN
STEAM
CONDENSATE
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Isolation Condenser Phenomena
IC Loop Flow Resistance
Low Pressure Steam Condensation
Condensation Heat Transfer in thePresence of Non-Condensable Gases
*Shell-side Convection Heat Transfer
* Same as for Emergency HeatExchangers
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IC Flow Resistance
The behavior of two-phase fluids in loops is particularlycomplicated.
The pressure drop and heat transfer coefficientsinside the condenser tubes are dependent on thetwo-phase flow pattern.
Two-Phase flow regime behavior are time
dependent. Two-Phase Friction Factor multipliers typically used.
(See summary by Saha, 2005, IAEA-TECDOC-1474
Nayak showed the influence of different two-phasefriction factor multiplier models on steady state naturalcirculation. Nuc lear Engineering and Design , 237(4):386-
398, 2007. Concluded that all the friction factor models
overestimate the natural circulation flow rate (i.e.,underestimate pressure drop).
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Low Pressure Steam Condensation
Condensation occurs when a vapor is cooledbelow the saturation temperature to induce thenucleation of droplets. This can occur in one oftwo ways. Homogeneously within the vapor
Heterogeneously on particulate matter
Two types of heterogeneous condensation thatoccur in the isolation condenser are: Drop-wise and Film-wise.
Reliable theories of drop-wise condensation have notbeen established.
Many different condensation models have beendeveloped to predict the local heat transfercoefficients for both vertical and horizontaltubes, for detailed information refer to Collier,1996.
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Condensation Heat Transfer in the Presence of
Non-Condensable Gases (METU-CF Tests) NUREG/IA-0210, 2007
Single Tube countercurrent heat exchanger
Cooling water flows upward through a cooling jacket thatsurrounds the tube while the steam/air mixture flows downwardthrough the tube.
Axial temperature measurements provide for a heat balanceused to determine the axial heat flux through the tube walls.
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Temperatures in the lower section of the condenser tube increasewith time.
It is postulated that the reason for this behavior is that as steamcondenses, air concentration increases at the bottom of the tube.
Axial measurements of air concentration were not made for thesetests.
Condensation Heat Transfer in the Presence of
Non-Condensable Gases (METU-CF Tests) NUREG/IA-0210, 2007
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RELAP5/MOD 3.3 predicts air mass fraction is largest in the lowersection of the tubes.
Overall good agreement with the total heat load calculation
Condensation Heat Transfer in the Presence of
Non-Condensable Gases (METU-CF Tests) NUREG/IA-0210, 2007
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Good agreementwith data has beenobtained bycorrelations
developed bySiddique andHasanein
Correlations for Condensation Heat Transfer in the Presence of
Non-Condensable Gases
0.433 1.249 .624.537Re hNu W Ja
Siddique Steam/Helium Correlation
h0.02 < W 0.52
300 Re 11,400
0.004 0.07Ja
Range:
Hasanein Steam/Helium Correlation
Range:
.327 2.715 1.058
.199ReNu Sc Ja
0.314 < Sc 0.864
846 Re 26537
0.007 0.102Ja
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Condensation Heat Transfer Correlation for mixtures of Steam,Helium and Air.
Correlations for Condensation Heat Transfer in the Presence of
Non-Condensable Gases
Hasanein Steam/Helium/Air Correlation
Range:
0.256 0.741 0.9521.279Re 1 1.681 a hNu W W Ja
h
a
0.023 < W 0.405
0.000 < W 0.574
846 Re 24,460
0.007 0.102Ja
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Experiment Tubes Pressure
(MPa)
NC Mass Fraction Codes
MIT, USA
Steam/Helium [18]
1 Tube
46 mm ID
2.54 m Length
0.1-.6 0.02-0.2 He
MIT, USA Steam/Helium/Air [18] 1 Tube
46 mm ID
2.54 m Length
0.1-.6 0.02-0.2 He
0.045-0.2 Air
Purdue University [19]
Steam/Air
1 Tube
25.4 mm ID
50.8 mm ID
2.1 m Length
0.2-0.5 0.0-.05 Air RELAP5-MOD3.3
UC-Berkeley, USA [20]
Steam
1 Tube
47.5 mm ID
2.4 m Length
0.1-0.5 Pure Steam
UC-Berkeley, USA [20] Steam/Air 1 Tube
47.5 mm ID
2.4 m Length
0.1-0.5 0.01-0.4 Air
UC-Berkeley, USA [20]
Steam/Helium
1 Tube
47.5 mm ID
2.4 m Length
0.40 0.003-0.15 He
METU-CF [17]
Middle East Technical University,
Turkey
Steam/Air
1 Tube
33.0 mm ID
2.158 m Length
0.23-0.28 0.0-1.0 Air RELAP5-MOD3.2
RELAP5-MOD3.3
UMCP [17]
University of Maryland, USA
Steam/Air
28 Tubes
30 mm ID
3.9 m Length
0.41 0.0-1.0 Air RELAP5-MOD3.2
RELAP5-MOD 3.3
PIPER-ONE [9]
Steam
12 Tubes
20 mm ID
0.4 m Length
4-5
0.5
Pure Steam RELAP5-MOD2
RELAP5-MOD3
PANDA PSI [16]
(ISP-42)
Steam/Air
20 tubes
50.8 mm
1.778 m Short Tubes
2.066 m Long Tubes
0.1-0.3 Steam-Air RELAP5
CATHARE
GOTHIC and Others
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Department of
Nuclear Engineering
& Radiation Health Physics
Conclusions for Phenomenon #13
Emergency Heat Exchangers Single-Phase Natural Circulation well understood in terms of
buoyancy, loop resistance and tube-side convective heattransfer
Greatest uncertainty on shell side heat transfer due to
coupling to flow patterns in IRWST and variations in localheat transfer coefficients
APEX PRHR overall heat transfer coefficients for naturalcirculation conditions varied from U = 450-1100 W/(m2-K)
Isolation Condensers Correlations of Siddique and Hasanein appear to predict tube
data reasonably well within the ranges specified
The most comprehensive code comparisons to prototypic ICdata is ISP- 42, using the PANDA test facility at PSI inSwitzerland.
Research efforts continue NACUSP at PSI