15_behavior of emergency heat exchangers and isolation condensers.ppt

7/27/2019 15_Behavior of Emergency Heat Exchangers and Isolation Condensers.ppt

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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


2/24

Department of

Nuclear Engineering


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.


5/24


6/24

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


13/24

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.




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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




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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


24/24

Department of

Nuclear Engineering


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

15_behavior of emergency heat exchangers and isolation condensers.ppt

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