100
KAERI/TR-1321/99 KR9900259 A Study on Critical Heat Flux in Gap Korea Atomic Energy Research Institute 31-02
KAERI/TR-1321/99
KR9900259
A Study on Critical Heat Flux in Gap
Korea Atomic Energy Research Institute
3 1 - 0 2
1998
1999. 4.
21
- I -I@ff BLAMK
°f
II.
TMI-2
l-71 4]5>^ ^ ^ s > 3 1 $lfe SONATA-IV(Simulation Of Naturally Arrested Thermal
Attack In-Vessel) W ^ I ^ ^ r - ^ - S . ^ CHFG(Critical Heat Fux in Gap) -M^^r ^ ^ 5 > a l
#$171
III.
CHFG € ^ ^ r #=?•% ?1^<*\}*\ ̂ ^91^}°A # ^ 371(0.5, 1.0, 2.0, 5.0
71̂ 51 %& tt
^ y l M ^ R-H3
- iii -
^ CFX-F3D
.o .^ , CHFG CCFL(Counter Counter Flow Limit)
IV.
71 ̂ s ]
CHFG 717]- ^71-to]]
. R-113-8:
R.i 13 40 %7V 5 ] ^ 3 3 ^
10
. .g.
71^21
CCFL
CFX-F3D
- iv -
CHFG
CHFG
CCFL CHFG CCFL
5514.
V.
- v -
SUMMARY
I. Report Title
A Study on Critical Heat Flux in Gap
II. Objective and Importance of the Study
As a part of the SONATA-IV(Simulation Of Naturally Arrested Thermal Attack In-Vessel)
program, performing to verify the cooling mechanism of the corium in the lower plenum during
severe accident in the TMI-2 nuclear power plant, an experimental study of the CHFG(Critical
Heat Flux in Gap) have been performed to measure the critical power and to investigate the
inherent cooling mechanism, because there has been no experimental data on CHF in
hemispherical narrow gaps
III. Scope and Content of Study
The scope and content of this technical report is to perform the test on critical heat flux in
hemispherical narrow gaps using distilled water and Freon R-113 as experimental parameters,
such as system pressure from 1 to 10 atm and gap thickness of 0.5, 1.0, 2.0, and 5.0 mm. The
experimental results on critical power were compared with the existing correlation, developed in
flat plate and annuli gaps. The distilled water data on critical power were also compared with the
Freon R-113 data. The conduction heat transfer in the copper shell has been performed to verify
- vii -
the experimental results using CFX-F3D computer code. The CCFL(Counter Counter Flow
Limit) test is being performed to evaluate the CHFG test results on critical power in
hemispherical narrow gaps.
IV. Results of the Study
The test results have shown that even if local dryout occurs, there exists a quasi-steady state
and the temperature of the dryout region is limited within a certain value. When the heater power
is large enough, however, there is no quasi-steady state. The dryout region expands by itself
without an increase in heater power, finally leads to a global dryout, and the temperature of the
heater surface monotonically increases. The heat flux bringing about that situation is defined as
the critical power in the present experiments.
The CHFG test results have shown that the measured values of critical power are much lower
than the predictions made by empirical CHF correlations applicable to flat plate gaps and annuli.
The pressure effect on the critical power was found to be much milder than predictions by those
CHF correlations. The values and the pressure trend of the critical powers measured in the
present experiments are close to the values converted from the CCFL data. This confirms the
claim that a CCFL brings about local dryout and finally, global dryout in hemispherical narrow
gaps. Increases in the gap thickness lead to increase in critical power. The measured critical
power using R-113 in hemispherical narrow gaps are 60 % lower than that using water due to the
lower boiling point, which is different from the pool boiling condition.
The CFX-F3D results on conduction heat transfer have shown that the copper shell contacts
with heater very well during CHFG tests. The heat conduction in the copper shell is effective on
copper shell temperature in CHF(Critical Heat Flux) condition. The CCFL(Counter Counter
Flow Limit) test facility was constructed and the test is being performed to estimate the CCFL
- viii -
phenomena and to evaluate the CHFG test results on critical power in hemispherical narrow gaps.
V. Proposal for Application
The present experimental data on critical power in hemispherical narrow gaps, which is only
in the world, will be used computer code development on in-vessel corium coolability issue.
Further studies are needed to investigate the high-pressure effect on critical power because the
electrical power is limited in the present test.
- ix -
CONTENTS
Chapter 1. Introduction 1
Chapter 2. Experimental Contents and Method of CHFG 5
Section 1. Experimental Facility 5
Section 2. Experimental Methodology 12
Chapter 3. Experimental Results and Discussion of CHFG 15
Section 1. Experimental Results and Discussion using Distilled Water 15
Section 2. Experimental Results and Discussion of using Freon R-113 24
Section 3. Estimation ofThermal Conductivity Effect in the Copper Shell 29
Section 4. Comparison and Discussion of Experimental Data 37
Chapter 4. Experimental Contents and Method of CCFL 45
1. JQAUClilllClltCll
Section 3. Experimental Methodology 50
Chapter 5. Conclusion and Recommendation 53
Chapter 6. References 55
Appendix 1. Detailed Description of the CHFG Test Facility 59
Appendix 2. CFX-F3D Input 73
Appendix 3. Published Paper on CHFG Test in International Journal 81
- xi -
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- 27 -
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CHFG4 VISU-n ^ ^ ^ W < ^ ^T 1 ^ ^ ^ ^ ^ ^ ^^1*^(critical powerH
^aofl-H CCFL
CCFL ^ ^ ^ r ^ ^ ^ M " ^ ° 1 ^r^ cm ̂ ^r ^ m <% o]a.fe
CCFL l̂] &%: ^ ^ f e ^ 1 ^ 4 - ^ ^^^1
] C C F L
3. ^ ^ . s . 40]ol] ^ ^ ^ ^ o . 3.4x6] 3 7 | 7 } CCFL o
dryout)
CCFL ^ ^ » ^r^^b 7]# <2^SM: # ^ S . ^ Mayinger
- 45 -
bypass[4.1], Lee
Cheng [4.3], Mishima^ Nishihara[4.4] ^ Sudo ^ Kaminaga[4.5]
915. ^ ¥ 3 § 7 > ^ o ] ^ 5 H ^ t j . . Koizumi ^ [
CCFL ^ ^ i ^
^ ^ - ^ 0.5 - 5.0 mm
CCFL sM- ^^^1-^4.
1̂ 1 ^ ^ € 7]^S] CCFL ^ £ tfl^-^- a |^o | io cm °]
s.^ol 4a.>fl
CCFL ^ ^ # ^l-«>^o) ^ tfl^
^l CCFL S-t^- ^ ^ tflo^fe 4^-2^ ^ 4 ^o] Wa l l i s
Kutateladze ̂
= CW (4.1)
= Ck (4.2)
= j k 4 fi* (4.3)
- 46 -
f. Kutateladze
Taylor 3^-g ; o]-g-*>fe M Wallis ^ ^ M ^ f e 3 3 , # ^ 3 3.7], ^ ^-^
r ^ s m CCFL4
Kutateladze ^7>
Wallis 4 ^ D 1 ^ ^ ^21 4-8-^12. $14. CCFL
. Sudo^f Kaminaga [4.5]fe
^V-̂ -̂ l 3.7] S » , 0sakabe4 Kawasaki[4.8]fe -fi-S.̂ ) <̂>1 W # , Mishima ^
Ishihara[4.4]Tr 2 «fl^ -fi-S ^^1 2W«r ^ - ^ ^ ° l S . ^ ^ § } ^ 4 . °14 y l * ^ :
# 3 M ^-^ ^ - S . ^ ^ S . 5Jt|-. Lee -f-[4.2]4 Koizumi ^[3.10]^: ^7]-3J ^(equivalent
diameter)^: ^^^<>)S, <>]•%•$: ^ : ^ Richter[4.9]fe
2.
CCFL
- 47 -
1. water reservoir2. air buffer3. pump4. flow meter
5. level guage6. central pole7. inner cylinder8. acrylic pipe
9. watering holes10. flow distributor
4.1 CCFL
- 4 8 -
OdHO ^
- lo M ? ^ l ^ ^l-afeU' -kfc. -i-b log^b -bio unu osz -b UIUI 00?
ta IXA-dH t̂
H3A-dH
* • £ ^
kk l- t o - ! ? *
mm fe
71 fe ±0.3 mm
CNC
250 mm
3.
CCFL
(1)
(2)
(3)
(4)
(5) (4)S]
(6)
(7)
37](0.5, 1.0, 2.0, 5.0 mmH
71S) -B-^^i- 32.3*1?! f̂l 10
CCFL
(8)
- 50 -
(9)
nfl
. 500^ mm ^ - ^ CCFL ©1
fe CCFL
CCFL
- 51 -
CHFG ^ ^ CFX-
CHFG
CCFL
CCFL ^ ^
o]2.7ll
CHFG
CHF
CCFL
VISU-II CCFL
- 53 -
^3]£r R-113
^ 4 0 %7> 5 ] ^ ^ ^
Sf 10
CFX-F3D CHFG
H7l7> 5.0 mm
CCFL ^ ^ ^
- 54 -
3L
1.1 T. G. Theofanous, C. Liu, S. Addition, S. Angelini, O. Kymalainen, and T. Salmassi,
"In-Vessel Coolability and Retention of a Core Melt," DOE/ID-10460, Vol. 1&2, 1995
1.2 O. Kymalainen, H. Tuomisto, and T. G. Theofanous, "In-vessel Retention of Corium at
the Loviisa Plant," Nuclear Engineering and Design, Vol. 169, pp. 109-130, 1997
1.3 J. L. Rempe, J. R. Wolf, S. A. Chavez, K. G. Condie, D. L. Hagrman, W. J. Carmack,
"Investigation of the coolability of a continuous mass of relocated debris to a water-filled
lower plenum," EGG-RAAM-11145, 1994
1.4 J. R. Wolf et. al , "TMI - 2 Vessel Investigation Project Integration Report,"
NUREG/CR-6197 (EGG - 2734), 1994
1.5 S. B. Kim et.al., "Recent Progress in SONATA-IV Project," OECD/NEA CSNI PWG-2,
The Third Mtg. Of TG-DCC, Rockville, MD, USA, May 9-10, 1997
1.6 K. Y. Suh et al., "SONATA-IV Simulation Of Naturally Arrested Thermal Attack In-
Vessel," Proc. Int. Conf. on PSA Methodology and Applications, pp. 453-460, Seoul,
November 26-30, 1995
1.7 K. H. Kang et al., "Experimental Investigations on In-Vessel Debris Coolability through
Inhererent Cooling Mechanisms, OECD/CSNI Workshop on In-Vessel Core Debris
Retention and Coolability," Garching, Germany, March 3-6, 1998
1.8 J. H. Jeong et al., "Experimental Study on CHF in a Hemispherical Narrow Gap,"
OECD/CSNI Workshop on In-Vessel Core Debris Retention and Coolability, Garching,
Germany, March 3-6, 1998
1.9 W. Kohler, H. Schmidt, O. Herbst, W. Kratzer, "Experiments on heat removal in a gap
between debris crust and RPV wall," OECD/CSNI Workshop on In-Vessel Core Debris
EC _DO
Retention and Coolability, Garching, Gennany, 1998
1.10 K. H. Bang et al., "Boiling Heat Transfer in Narrow Spaces and Its Implications for
Lower Head Integrity during a Severe Accident," Proc. Int. Top. Meet, on Probabilistic
Safety Assessment, pp. 1206-1211, Park City, Utah, 1996
1.11 t W , ^ 1 ^ , ?M3L, o l « , ^%Tt, "?% ^± *H^HS} ^ t ^
7}X\$- ̂ ^,"cfl^7l^l^-sl^7il^-#tHs] fe^ B, pp. 105-109, 1996
1.12 3*1$ S], "tiV t̂g ^of l^o] «1^7M^- ^ , " ^ € * r 3 * N '97 ±A]
^-#^^51 fe-g-^1, *fl 1 ̂ , pp. 575, a^tfl^SL, 1997 Vl 5 ̂ 30 ̂ -31 «g
1.13 J. H. Jeong, R. J. Park, and S. B. Kim, "Visualization Experiments of the Two-Phase
Flow Inside a Hemispherical Gap," Int. Commu. Heat & Mass Transfer, Vol. 25, No. 5,
pp. 693-700, 1998
-^,"KAERI/TR-1027/98, ^ ^ f ^ T 1 ^ , 1998 Vl 4 ^
3.1 P. B. Whalley, Boiling, "Condensation and Gas-Liquid Flow," Oxford, U.K., Oxford
University Press, 1987.
3.2 W. Peyayopanakul and J. W. Westwater, "Evaluation of the Unsteady-state Quenching
Method for Determining Boiling Curves," Int. J. Heat Mass Transfer 21, pp. 1437-1445,
1978
3.3 M. S. El-Genk and A. G. Glebov, "Transient Pool Boiling from Downward-facing Curved
Surfaces," Int. J. Heat Mass Transfer 38, pp. 2209-2224, 1995
3.4 "CFX-F3D Code User Manual," AEA Technology, 1995
3.5 "MATLAB New Features Guide Version 4.0, " The MATH WORKS Inc., March 1003
3.6 Y. Chang and S. Yao, "Critical Heat Flux of Narrow Vertical Annuli with Closed
Bottoms," J. of Heat Transfer 105, pp. 192-195, 1983
3.7 M. Monde., H. Kusuda, and H. Uehara, "Critical Heat Transfer during Natural
Convective Boiling in Vertical Rectangular Channels Submerged in Saturated Liquid," J.
Heat Transfer 104, pp. 300-303, 1982
3.8 Y. Katto and Y. Kosho, "Critical Heat Flux of Saturated Natural Convection Boiling in a
Space Bounded by Two Horizontal Co-axial Disks and Heated from Below," Int. J.
Multiphase Flow 5, pp. 219-224, 1979
3.9 R. E. Henry and R. J. Hammersley, "An Experimental Investigation of Possible In-Vessel
Cooling Mechanisms," CSARP Meeting, Bethesda, Maryland, 1997
3.10 "Modular Accident Analysis Program User's Manual," EPRI, 1994
3.11 Y. Koizumi, H. Nishida, H. Ohtake, and T. Miyashita, "Gravitational Water Penetration
into Narrow-gap Annular Flow Passages with Upward Gas Flow," Procs. Of NURETH-8
1, pp. 48-52, 1997
3.12 N Zuber, "Hydrodynamic Aspects of Boiling Heat Transfer," AECU-4439, 1959
4.1 F. Mayinger, P. Weiss, and K. Wolfert, "Two-Phase Flow Phenomena in Full-scale
Reactor Geometry," Nuclear Engineering and Design 145, pp. 47-61, 1993
4.2 S. C. Lee, C. Mo, S. C. Nam, and J. Y. Lee, "Thermal-hydraulic Behaviours and
Flooding of ECC in DVI Systems," KAERI Report, KAERI/CM-045/95, 1995
4.3 L. Y. Cheng, "Counter-Current Flow Limitation in Thin Rectangular Channels," BNL
Report, BNL-44836, 1990
4.4 K. Mishima and H. Nishihara, "The Effect of Flow Direction and Magnitude on CHF for
Low Pressure Water in Thin Rectangular Channels," Nuclear Engineering and Design 86,
pp. 165-181, 1985
4.5 Y. Sudo and M. Karhinaga, "A CHF Characteristic for Downward Flow in a Narrow
Vertical Rectangular Channel Heated from Both Sides," Int. J. Multiphase Flow 15, pp.
755-766, 1989
- 57 -
4.6 G. B. Wallis and S. Makkenchery, "The Hanging Film Phenomenon in Vertical Annular
Two-Phase Flow," J. Fluids Engineering 96(3), pp.297-298, 1974
4.7 S. S. Kutateladze, "Heat Transfer in Condensation and Boiling," USAEC Rep-tr 3770,
1952
4.8 M. Osakabe and Y. Kawasaki, 'Top Flooding in Thin Rectangular and Annular
Passages," Int. J. Multiphase Flow 15, pp. 747-754, 1989
4.9 H. J. Richter, "Flooding in Tubes and Annuli," Int. J. Multiphase Flow 7, pp. 647-658,
1981
- 58 -
bd CHFG
- 59 -
I
NOZZLE TABLE
SERVICE
DEMI WATER IN
VAPOR OUTLET
CONDENSATE INLET
PT CONN.
PSV CONN.
UT CONN
LT CONN.
TYPE MAT'L RATING
BW/C
FLO
8WC
BW/C
BW/C
BWtBW/C
SUS3O4
SUS304
16KO
16KO
BUTT WELD CONNECTOR
(H0KE-8CBW8)
EOD-410197.01.04 09: ii
HOLD HEATERSEE DETAIL SEE DETAIL
ASSEMBLY
DESIGN CONDITIONS
PRESSURE IS kq/cma
TEMPERATURE: 300
OPERATION CONDITIONS
PRESSURE 10
TEMPERATURE: 200CODE CODE STAMP
MAWP
SHELL SPEC.. SUS 304B0WID x 320H xt7t
JOINT EFFOISH SPEC.
85SSUS 304
600(10 X 300H x 201JOINT EFF.CLADDING OR LININO SPEC
85X
OASKET SPEC.SUPPORT SPEC.EXTERNAL PIPE SPEC.INTERNAL PIPE SPEC._FIANGF 5PEC.
METAL4-3UPP0RT LUO
SUS 304
RAT1N0L.FACING-
JIS 18 kg/em*SO/RF
SUS PART SANOINOGLASS WOOL lOOt
_OPERATINO WT_ TFST WT
PAINT
INSULATION
FtREPROOFIN0_
SHIPPING WT._
ELEVATION MEASURED FROM BASELINE.
ORIENTATION MEASURED CLOCKWISE FROM 0* SUREO
PROJECTION MEASURED FROM C OF VESSEL TO
EXTREME FACE OF FLANGE. PROOF
LUO
NOZZLE STANDARD
TITLE
STD-1020
STD-1007
DRAWING NO.
REFERENCE DRAWING
SHIKSUNG CAM PLANT CO., LTD.SCALE
A3, 1/10
A
A
PROJECT NO.61217
DESCRIPTION DATE DRAWN! CHK'D APP'D
APP'D BY CHK'D BY DON'D BY ORAWN 8Y
LEE Y. S.
TITLER-101
REACTOR
DWG NO.
EQD-4101
REV.
SHINSUNG CAM PLANT CO., LTD.Sheet No. EDS-4002
HEAT EXCHANGER DATA SHEETRevision
Date
Checked by
Plont SONATA-rV / CHFG
Client KAERI
Item No.E—111
Project No. 61217 Service CONDENSER
Locotion TAEJON. KOREA No. Required ONEHeot Duty 34.000 Kcol/Hr Shells/Unit
Ht. Trans. Area per Unit 0.5 ml Ht. Trans. Areo per Shell 1.0
Code TEMA
PERFORMANCE OF ONE UNIT CONSTRUCTION
Shell Side Tube Side No. of Tubes per Shell
Fluid VAPOR C.W Tube Size , m m 14.85 'D X 19.05 0 0 . (BWG 14 )Tube Length 600Tube Loyout Pitch 25.4 mm
Fluid Vop'd or Conds'd WATER Shell Oio. 8B
Flow Rote Kg/Hr 64 6800 Boffle Spocing 100
Density Kg/m 1000 Boffle Cut Hori. D Vert. H •40
Viscosity CP 1.0 Insulot'n, Shell/Chonn.. Hot/Cold
Sp. Heot Kcol/KgX 1.0 Pointing SANDING
Them. Cond. Kcol/mHrX
Latent Heot Kcol/Kg MATERIAL
Temp. In •c 180 32 Shell SUS 304 Channel SUS 304Temp. Out 37 Chonn. Cov. SUS 304 Flating Heod SUS 304
Op. Press. Kg/cm 3 10 Backing Device Poss Port. SUS 304
No. ot Posses per Shell Tub* SUS 304 Tube Sh't SUS 304
Velocity m/sec Boffle SUS 304 Impingem't
Press. Drop. Kg/cm Tie Rod SUS 304 Bofl Spocer SUS 304Design Temp. •c 300 100 Saddle SUS 304 Gosket
Kg/cm'-GDesign Press. 16 10 No22le Shell Chann. METAL
Press. Test. Hydro Kg/cm' - G 10 10 Shell side SUS 304 Flooting METAL
Pneu. Kg/cm2 - G 10 10 Chonn. side SUS 304 Shell nozz. METAL
Rodiogroph Flonge Chonn. nozz. PTFECon*. Allow. Shell nozz. SUS 304 Bolting
LMTD Corrdcted 145 X Chonn. side SUS 304 Shell Chonn. FC25C
Uo. Colc./Service 500 Kcol/W HrT Chann. end SUS 304 Flooting FC25C
CONNECTIONS Chonn. nozz. SUS 304 Shell nozz. FC25CMork Size Roting/Focing Service Chonn. nozz.N-1 11/2B 16K/RF VAPOR INLETN - 2 1/2B 16K/BWC COND. OUTLET
Tie Rood SUS 304
N - 3 IB 5K/SOC C.W INLETNOTE: BAFFLE WITH V-NOTCHING
N-4 IB SK/SOC C.W OUTLETN - 5 1/2B 16K/BWC VENTN-6 1/2B 16K/BWC DRAINN - 7 1/2B 5K/SOC DRAIN ENG. DW5. NO. EQD-4102
SKFI.TON DRAWING
<S3>
SSFM-713 App'd by
Date
Chk'd by
Dote
Prep'd by
Date
- 62 -
SHINSUNG CAM PLANT CO., LTD. Sheet No. EDS-4001
TANK & VESSEL DATA SHEETRevision
DoteCheeked by
Plant SONATA-IV /CHFC
Client KAERI
Item No.R-101
Project No. 61217 Service REACTOR
Location TAEJON. KOREA No. Required ONERegulation Code. Type/Norm. Cop. VIR. / 906.
OPERATING CONDITIONS
Process fluid WATERSpecific gravity •c Viscosity C.P. @ •cHeat Transfer N o D Heating, Cooling.D Ht. Trans. Device
Agitation Yes O Not Agitofn Device Mech.p Uq. Circ. Q
Op. Temp.. Trim 180 'C Op. Press.. Trim 10 Kg/cm' —G. mmHg—A
Jkt/Coil "C Jkt/Coil Kg/em1 —G. mmHg—A
DESIGN CONDITIONS
Design Temp. 300 *CDesign Press.. Trim 16 Kg/cm' - C
Jkt/Coil Kg/cm' -G
Press. Test.Hydro./Pneum.
Radiograph
Wind Load
10/10 Kg/cm' -G
Stress Relief
Seismic Coeff.
Corr. Allow.
CONSTRUCTION
Shell ID/Length * 600 mm/ 620Head type 10%-DishedD 2 : 1 Elip. D
Support Saddle D LugQ Leg D
Insulation: (fig). Cold 100
Ladder Yes D No Plotform Yes D No fa*
Insulation Ring Yes D No (2
Pointing SANDING
Weight: Empty Kg, Op Kg
MATERIAL
Shell SUS 304 Head
Support SUS 304
Flange SUS 304
SUS 304
Nozzle SUS 304
Gasket METAL
Lining Spec.
CONNECTIONS
MarkN - 1
N-2N-3N - 4
N-5
N-6N-7
Size1/2B11/2B1/2B1/2B1/2B1/2B1/2B
Roting/Facing16K/BWC16K/RF
16K/BWC16K/BWC16K/BWC
16K/BWC16K/BWC
Service
DEMI WATER INLET
VAPOR OUTLET
COND. INLET
FT CONN.
PSV CONN.
LT CONN.
LT CONN.
SKELTON DRAWING
iwmt
SSFM-710
ENG. DWG. NO.
NOTE:
App'd by
Date
EQO-4101
Chk'd by
Date
Prep'd by
Date
- 63 -
SWNSUNO CAM PLANT CO..LTD. EOO-410IB
R-1O1 REACTOR / SHELL DETAILsoHAU-iv / oro
Preset H»
I
24B FLANGE24-J9* HOLES
«fiO7 5SHril /DISH
S-1/1O
E0D4101B97.01.04 09:46
24-390 HOLES
«S39 SHFII / DISH nFTAII
HW0 3JI
Dol« IM6.08.M Dolt
5
I
ii
091 Oil 091
. 08f
\
©
1
I
c
UJ
o
o
to
to
oT
- 65 -
SHINSUNG CAM PLANT CO..LTD. SmlK*. EQ0-4101DnzR-101 REACTOR / MOLD HEATER DETAIL
SOHtTA-IV/OfO
20kw x 2EA HEATER
557°° x 357" x 2001 SHEa PLATECOVER FUWOE
SUS 304
enO)
•557
20t COPPER (SEE OET.)
' A ' 0ETAH
20kw HEATER440V x it
MOLD HEATFR DETAIL
S.1/10
EOD4I01D97.0t.04 09:57
M< 1M&01M CW.
o55*
8
o
UJ
oUJ
Q.
CtLO
UJ
o
toz6 E S
*
I
- 67 -
SHINSUNG CAM PLANT CO..LTD. !Mlk IOT-J001HZEQUIPMENT LAYOUT S-t/50
SCHATA-IV/CHfO
Cllwt KAEBI
*50 350 I 500
1500
200
LOT-300197.01.04 09:44
CL+1580
TOP VIEWS-1/ftO
FRONT VIEW
( X
• M i l ,
SIDE VIEW..5-1/20.
H0MO3JL
Dol. ltW.03iOt
SHINSUNG CAM PLANT CO..LTD. LOT-30021 /
SUPPORT FRAME S-1/20Wont SOWU-IV / CWO HtvWcri
IOO1IPro»ct H t 81217
IOT-300296.12.27 10:33
1500
4-CHWNEL /(100x50x5)
c-100x50x5
TOP VIEWC-75x40x5
OL+1280
4.5t CHECKED PLATE
a+soo
OH-0.00
500
C-100x50x5
200
1500
600 . 1 . 400 ,
•"T~1
61 REINFORCINO PLATE
(200x200)
20t BASE PUTE(200x200)
AC-I00x50x5
1000
FRONT VIEW SIDE VIEW
MOW8J,
Ool. IM&DUK
SHINSUNO CAM PLANT CO..LTD. EQO-4102A
E-111 CONDENSER / T U B E SHEET DETAILSOWAU-IV / O f 0
KAOtl81217
8B FLANGE (16KO)35tf»x XS^x 261SO/ftF TYPE
FOR 3/4B TUBE WELOINOA PITCH - 25.4
EQD41O2A97.01.03 11:50
TtlRF SHFFT DETAII
• 5 - 1 / 2 .
M l
* * * * *
34-3/4B TUBEA P1TCH-25.4
50 400
(53)
100too 100 100
JL uA.
T
SO 50
4¥ ¥*Spj.70
100 500
5050 50
100
ASSEMBLY
NOTE
• TUBE CONNECTION TO TUBE SHEET
TO BE SEAL WELDEO WITH EXPENDING
• BAFFLE CUT 40X (VERTICAL)
• BAFFEL WITH V-NOTCHINO
• BHA: : BUTT WELD CONNECTOR(HOKE : 8C8W8)
EOO-410297.01.04 10:00
HEAT EXCHANGER DATA SHEET
NOZZLE TABLE
M.K.
N-1
N-2N-3
N-5
N-6
N-7
SIZE
IViB
1/2BIB
IB
1/2B
V2B
SERVICE
VAPOR INLETCOND. OUTLET
C.W INLET
C.W OUTLET
VENT
DRAIN
DRAIN
TYPE
FLO
BVI/C
SOC.
SOC.
8W/J
BW/C
SOC
MAT'L RATING
SUS304
SUS304SGP
SOP
SUS304
SUSJ04
SOP
16kg
16kg5kg
5kg
16kg
16kg
5kg
NO77I F ORIFNTAT1ON
COOE : KS B623O
FLUIO ALLOCATION
FLUID
OISIGN PRESSURE
OPERATION PRESSURE
DESIGN TEMPERATURE
INLET TEMP.
OUTLET TEMP.
SHELL SIDE
VAPOR
18 kg/cm'
10 kg/cm'
300
180
TUBE SIDE
aw.10
3 kg/cm'
100
32
37
FLUID ALLOCATION
TEST PRESSHYDRO.
PNEU.
NUMBER OF PASSES
CORROSION ALLOWANCE
STRESS RELIEVED
SHEU SIDE TUBE SIDE
10
10 kg/cm!
1
1.0 ni/tn
10
10 kg/cm9
0.5
NO D Y E S ^ N O
REMARKS
RADIOGRAPHED
D FULL D SPOT [ NO
JOINT EFFICIENCY
INSULATION
SIZE
LENGTH
85X
500 NO. 34METAL
DESIGN CONDITIONS
<T U BE) PRESSURE 16 kq/cm3
TEMPERATURE: 300
OPERATION CONDITIONS(TUBE) PRESSURE 10 kg/cm
TEMPERATURE: 200COPE COPE STAMP
SHELL SUS3048B (200») x 5C0L
JOINT EFF
TUBE S P E C .
85%SUS304, SEAMLESS
3/48 x BWS14 (2TU)JOINT EFF.
CLAOO1N0 OR LINING S P E t _
ssx
GASKET SPEC.
SUPPORT SPEC.
EXTERNAL PIPE SPEC. .
INTERNAL PIPE SPEC._
RANGE SPEC
SUS METAL2-SAODLES
SUS304
RATINO-
FACINO-
16ko/fcm»SO/ttF
PAINT
INSULATION
FIREPROOFINO.
SHIPPING WT._
SUS SANDINO
_OPERAT1NO TFST WT
ELEVATION MEASURED FROM BASELINE.
ORIENTATION MEASURED CLOCKWISE FROM 0 ' SUREO
PROJECTION MEASURED FROM t OF VESSEL TO
EXTREME FACE OF FLANGE. PROOF
STEEL SADDLE
NOZZLE STANDARD
TITLE
STO-1021
STO-1003
0RAWINO NO.
REFERENCE DRAWING
S I * CAM PLANT CO, LIB.SCALE
AAAA
P R O ^ C T N O .
DESCRIPTION DATE 0RAWN; CHK'O APP'D
APP'O BY CHK'D BY DGN'D BY 0RAWN BY
LEE Y. S.
TITLE
E-111CONDENSER
DWG NO.
EQD-4102
REV.
bd 2. CFX-F3D
- 73 -
/* CHFG Heater Configuration Simulation */
/* CASE 2 : Heater is in contact with 2/3 of the inner surface
/* PURE CONDUCTION PROBLEM V
»CFXF3D
»OPTIONS
TWO DIMENSIONS
HEAT TRANSFER
USE DATABASE
END
»MODEL TOPOLOGY
»CREATE PATCH
PATCH NAME 'SHELL'
PATCH TYPE 'CONDUCTING SOLID'
BLOCK NAME 'BLOCK-NUMBER-1'
PATCH LOCATION 130 110 11
PATCH GROUP NUMBER 1
END
»CREATE PATCH
PATCH NAME'Centerline'
PATCH TYPE 'SYMMETRY PLANE'
BLOCK NAME 'BLOCK-NUMBER-1'
PATCH LOCATION 30 30 1 10 1 1
HIGH I
END
»CREATE PATCH
PATCH NAME 'Outer Wall'
PATCH TYPE 'CONDUCTING BOUNDARY1
BLOCK NAME 'BLOCK-NUMBER-1'
PATCH LOCATION 1 30 10 10 11
- 75 -
HIGHJ
END
»CREATE PATCH
PATCH NAME 'Heated Inner Wall1
PATCH TYPE 'CONDUCTING BOUNDARY'
BLOCK NAME 'BLOCK-NUMBER-11
PATCH LOCATION 1130 11 11
LOWJ
END
»CREATE PATCH
PATCH NAME 'Naked Inner Wall'
PATCH TYPE 'CONDUCTING BOUNDARY'
BLOCK NAME 'BLOCK-NUMBER-1'
PATCH LOCATION 110 11 11
LOWJ
END
»MODEL DATA
»MATERIALS DATABASE
»SOURCE OF DATA
PCP
END
»FLUID DATA
FLUID 'AIR'
MATERIAL TEMPERATURE 293.0
MATERIAL PHASE 'GAS'
END
»TITLE
PROBLEM TITLE 'CHFG COPPER SHELL CONDUCTION PROBLEM'
END
»PHYSICAL PROPERTIES
»SOLID HEAT TRANSFER PARAMETERS
PATCH GROUP NUMBER 1
DENSITY 8890.0
SPECIFIC HEAT 385.4
- 76 -
SCALAR CONDUCTIVITY 379.9
END
»SOLVER DATA
»PROGRAM CONTROL
MAXIMUM NUMBER OF ITERATIONS 25
OUTPUT MONITOR POINT 25 5 1
MASS SOURCE TOLERANCE 1.0E-6
ITERATIONS OF HYDRODYNAMIC EQUATIONS 0
END
»MODEL BOUNDARY CONDITIONS
»CONDUCTING BOUNDARY CONDITIONS
PATCH NAME 'Outer Wall1
TEMPERATURE 373.4
END
»CONDUCTING BOUNDARY CONDITIONS
PATCH NAME 'Heated Inner Wall1
HEAT FLUX 105000.
END
»CONDUCTING BOUNDARY CONDITIONS
PATCH NAME 'Naked Inner Wall'
HEAT FLUX 0.
END
»OUTPUT OPTIONS
»DUMP FILE FORMAT
FORMATTED
NUMBER OF SIGNIFICANT FIGURES 8
END
»STOP
- 77 -
1/3°1 dryout
/* CHFG Effect of Dryout Patch Simulation */
/* CASE 2:1/3 Outer Surface is Dried Off */
/* PURE CONDUCTION PROBLEM */
»CFXF3D
»OPTIONS
TWO DIMENSIONS
HEAT TRANSFER
USE DATABASE
END
»MODEL TOPOLOGY
»CREATE PATCH
PATCH NAME 'SHELL'
PATCH TYPE 'CONDUCTING SOLID'
BLOCK NAME 'BLOCK-NUMBER-1'
PATCH LOCATION 1 30 1 10 1 1
PATCH GROUP NUMBER 1
END
»CREATE PATCH
PATCH NAME 'Centerline'
PATCH TYPE 'SYMMETRY PLANE'
BLOCK NAME 'BLOCK-NUMBER-11
PATCH LOCATION 30 30 1 10 1 1
HIGH I
END
»CREATE PATCH
PATCH NAME 'Heated Inner Wall'
PATCH TYPE 'CONDUCTING BOUNDARY'
BLOCK NAME 'BLOCK-NUMBER-1'
PATCH LOCATION 1 30 11 11
- 78 -
LOWJ
END
»CREATE PATCH
PATCH NAME 'Dry Outer Wall'
PATCH TYPE 'CONDUCTING BOUNDARY'
BLOCK NAME 'BLOCK-NUMBER-1'
PATCH LOCATION 1 10 10 10 11
HIGHJ
END
»CREATE PATCH
PATCH NAME Wet Outer Wall1
PATCH TYPE 'CONDUCTING BOUNDARY'
BLOCK NAME 'BLOCK-NUMBER-1'
PATCH LOCATION 11 30 10 10 11
HIGHJ
END
»MODEL DATA
»MATERIALS DATABASE
»SOURCE OF DATA
PCP
END
»FLUID DATA
FLUID 'AIR'
MATERIAL TEMPERATURE 293.0
MATERIAL PHASE 'GAS'
END
»TITLE
PROBLEM TITLE 'CHFG COPPER SHELL CONDUCTION PROBLEM'
END
»PHYSICAL PROPERTIES
»SOLID HEAT TRANSFER PARAMETERS
PATCH GROUP NUMBER 1
DENSITY 8890.0
SPECIFIC HEAT 385.4
- 79 -
SCALAR CONDUCTIVITY 379.9
END
»SOLVER DATA
»PROGRAM CONTROL
MAXIMUM NUMBER OF ITERATIONS 25
OUTPUT MONITOR POINT 25 5 1
MASS SOURCE TOLERANCE 1.0E-6
ITERATIONS OF HYDRODYNAMIC EQUATIONS 0
END
»MODEL BOUNDARY CONDITIONS
»CONDUCTING BOUNDARY CONDITIONS
PATCH NAME 'Heated Inner Wall'
HEAT FLUX 70000.
END
»CONDUCTING BOUNDARY CONDITIONS
PATCH NAME 'Dry Outer Wall'
HEAT FLUX 0.
END
»CONDUCTING BOUNDARY CONDITIONS
PATCH NAME 'Wet Outer Wall'
TEMPERATURE 373.4
END
»OUTPUT OPTIONS
»DUMP FILE FORMAT
FORMATTED
NUMBER OF SIGNIFICANT FIGURES 8
END
»STOP
- 80 -
- 81 - PA6ECS)left BLANK
Heat and Mass Transfer 34 (1998) 321-328 © Springer-Verlag 1998
Thermal-hydraulic Phenomena Relevant to Global Dryoutin a Hemispherical Narrow Gap
J. H. Jeong, R. J. Park, S. B. Kim
Abstract A series of experimental investigations on thecooling mechanism in hemispherical narrow gaps has beencarried out A visualization experiment, VISU-II, was doneas the first step to get a visual observation of the flowbehaviour inside a hemispherical gap and to understandthe mechanism inducing global dryout. It was observedthat the counter-current flow limitation (CCFL) phenom-enon prevented water from wetting the heater surface andinduced dryout The CHFG test was performed to measurethe critical power corresponding to global dryout and toinvestigate the inherent cooling mechanism in hemi-spherical narrow gaps. Temperature measurements overthe heater surface show that the two-phase flow behaviourinside the gaps could be quite different from the otherusual CHF experiments. The measured values of criticalpower are lower than the predictions by existing empiricalCHF correlations based on the data measured with small-scale horizontal plates and vertical annulus.
1IntroductionDuring the TMI-2 accident, the reactor pressure vessel(RPV) received no damage and molten corium was keptinside the pressure vessel and cooled down, despite thefact that all severe accident analysis codes predicted itwould fail. It means that there might be inherent coolingmechanisms that are not known. In order to explain thesafe cool-down of the relocated corium, three coolingmechanisms have been suggested and a gap-coolingmechanism is considered to be the most plausible one thatplayed the major role in corium cooling [1, 2]. Such amechanism works like this: When molten corium relocatesto the bottom of a pressure vessel filled with water, itshapes like a hemispherical pool and its surface formscrust As the corium is solidified it shrinks and the pres-sure vessel experiences creep due to high temperature andpressure, causing a gap to develop between the crust andthe pressure vessel. The water penetrates the gap and thecorium is cooled. In order for gap cooling to be effective,
Received on 14 April 1998
J. H. Jeong, R. J. Park, S. B. KimSevere Accident Research LabKorea Atomic Energy Research InstituteYusong P.O. Box 105, Taejon, 305-600, Korea
Correspondence to: J. H. Jeong
the gap size should be large enough and water shouldcontinue to be supplied through the gap so that the boilingheat transfer is maintained. The maximum power of a heatsource removable through boiling is the critical power. Atthe critical power, the whole of heated surface will be driedoff. Therefore, a study on a critical power in hemisphericalnarrow gaps is needed to assess the gap cooling mecha-nism.
If it is realistically possible to retain the molten coriuminside the lower plenum of the RPV, it is very beneficial tothe nuclear power plant designer. It is because they do notneed to consider the problems that may occur if themolten corium penetrates the RPV, like a direct contain-ment heating, an explosive interaction between molten fueland water and a concrete-melt interaction in the cavity.Such a situation is also desirable in terms of public ac-ceptance. Therefore, the gap-cooling concept became a hotissue in the field of severe accident research to achieveinvessel retention of molten corium. As the gap-coolingconcept was considered to be of importance recently, therehas not been many researches related to the concept. Someof them have focused on gap formation [3, 4, 5] and someupon the heat transfer through the gap [6, 7].
Some CHF studies have been carried out in various gapgeometries. Sudo and Kaminaga [8] and Katto and Kosho[9] performed CHF experiments in gaps of rectangularchannels and horizontal plates, respectively. Chang & Yao[10] carried out CHF experiments with test sections ofvertical annulus at atmospheric pressure and developedthe following correlations:
0.38(1)
where, <JCHF> g> D> Pi» Pg» hg> L and s are the critical heatflux, gravitational acceleration, diameter, liquid density,gas density, latent heat of evaporation, heated length andgap size, respectively. Monde et aL [11] carried out anexperimental study of the CHF at atmospheric pressure invertical rectangular channels. Three different heatingsurfaces (20, 35, 50 mm in length and 10 mm in width)were used and the gap size varied from 0.45 to 7.0 mm.They reported the following empirical correlation:
ICHF
Pgh?s
0.16
+ 6.7xlO-*(Pl/pg)°-6(L/s)(2)
where, a is the steam-water surface tension. Henry andHammersley [4] used Eq. (2) to assess the heat removal
- 83 -
capacity through gaps and this equation is currently usedin the MAAP4 code [12].
Up to now, however, there has been no experimentconcerning critical power and few studies on the two-phase flow behaviour in hemispherical gaps. An experi-mental investigation of which geometry is similar with ahemisphere was done by Kohler et al. [7]. The test sectionof their experimental facility is a scaled RPV and solidifiedcorium of the TMI-2 plant That is, the curvature of thelower plenum surface is shaped such that the angle ofinclination of the heating surface at the outer edge is thesame as the angle of inclination exhibited by the RPVlower head of TMI-2 at the edge of the solidified debriscrust. With the measurements, they reported that a gapsize of 1 mm is capable of transferring the decay heatproduced during the TMI-2 accident. In the TMI-2 acci-dent, around 19 tons of material relocated to the lowerhead, which is around 20% of the core materials (the corecontained 93.1 tons of fuel). So, in order to assess thecooling capacity through the gap for a more general situ-ation, it is necessary to do more experimental and ana-lytical investigations in addition to Kohler et al.'s [7] workwhich is case-specific to the TMI-2 accident.
A series of experimental investigations of the coolingmechanism in hemispherical narrow gaps, focusing on acritical power, have been carried out. The visualizationexperiment, VISU-II, and the first stage of the CHFG testshave been completed. The later one has been conductedwith water. The VISU-II test aims to get a visual obser-vation of the two-phase flow behaviour inside a hemi-spherical gap and to understand the mechanism inducingglobal dryout. The purpose of the CHFG experiments is toinvestigate the inherent cooling mechanism in a hemi-spherical narrow gap and find out critical power. Thename of the tests, CHFG, implies that the phenomena weare interested in are related to the critical heat flux.However, the term of critical power will be used instead ofCHF in the present work and the reason will be given laterin this paper.
Visualization Experiment: VISU-IIHydrodynamic instability was proposed by Kutateladze[13] as a CHF mechanism and his theory is generally ac-cepted. Therefore, understanding the hydrodynamic phe-nomena of boiling water in hemispherical narrow gaps isimportant in the study of critical power. Concerning thephysical phenomena associated with two-phase flow insidea gap, Kohler et al. [7] thought that an oscillating water/stream flow performs the necessary heat removal functionbetween the debris crust and the RPV wall. However thetwo-phase flow behaviour is not still well understood. Wecarried out experiments aiming to visualize boiling waterinside a hemispherical gap and see the hydrodynamicphenomena triggering dryout. In order to provide visualobservations, water and a hemispherical heater wereplaced in a transparent pyrex-glass vessel.
The VISU-II experimental facility consists of a hemi-spherical heater, power controller, a current/volt meter, abell-jar shaped transparent vessel and a PC for data ac-quisition. There is also a mirror, lighting and a Hi-8 home
video camera to visualize the flow inside the gap. We in-tended to make a 1 mm gap between the heater and pyrex-glass vessel itself. However, there exists some non-uni-formity due to the difficulty in machining the pyrex-glassvessel. The top of the pyrex-glass vessel is open to theatmosphere. Figure 1 shows a cross-section detailing thetest section, including the heater. An electric heater wireis located inside a hemispherical copper shell and the shellis filled with Wood's metal of melting point 70 °C. Thethickness and outer diameter of the copper shell are20 mm and 238 mm, respectively. The maximum heaterpower is 6 kW. Below the test section, a mirror slanting at45° is installed to provide a visual observation of the testsection bottom area.
The steam bubbles generated go upward alongside thehemispherical heater walL At the same time, water goesdown in the counter direction with the bubbles. The twophases flow violently in the gap and this flow patternprevails from the bottom to the top end of the gap. In thevicinity of the top end, steam tries to penetrate into thewater pool above the heater while water flows into the gap.They flow in counter directions through separated flowpaths. These flow paths are randomly established anddisappear quickly. Figure 2a shows the multiple flowpaths, the steam flow path is about 2 cm wide. At a certainelevated heater power, the mass velocity of steam reaches acritical value corresponding to the counter-current flowlimitation (CCFL). Jeong & No [14] named this type ofCCFL as entrance flooding because the CCFL is initiateddue to flow instability at the liquid entrance. That type ofCCFL occurs when the liquid entrance geometry is sharpand the liquid flow rate is large enough. In this case,hydrodynamic and geometric conditions around the topend of the gap influence the CCFL significantly but thoseconditions of the gap below the top end do not. The CCFLis also affected by the gap size. In our facility, CCFL firstoccurs at some part of the top end where the gap size issmall compared with the other part. According to obser-vations, steam and water still flow actively through mul-tiple paths in regions of larger gap sizes while CCFL occursin regions of smaller gap sizes. The heater surface just
Pyrexglass
Power line
/ ^ f / C lead wire
Water
Heater-
Copper-
Low melting alloy
Fig. 1. Cross-section of the test section
T/C
- 84 -
Top area
b Bottom area
Fig. 2a,b. Images of flow in the gap. a Top area; b bottom area
below the region where CCFL occurs is locally dried outbecause CCFL prevents water from penetrating the gap.With the heater power that initiated CCFL, the local dryoutregion was small and often re-wetted by the water comingup from the bottom. Since the test section was not so bigand the boiling two-phase flow fluctuated dynamically,water was able to reach the dryout region. With the furtherincrease in heater power, however, the dryout region wasenlarged and water could not reach it any more.Figure 2b shows the dryout region when the heater poweris 5.5 kW. The left-hand-side is filled with water while theright-hand-side is dried out.
CHFG Experimental FacilityThe VISU-II test gave us some phenomenological under-standings. However, it was not possible to perform boilingexperiments with the facility at elevated pressures sincethe vessel is made of fragile glass and the heater does notprovide uniform heat flux. So we designed a CHFG facilitytaking advantage of lessons from the VISU-II test. Figure 3shows the CHFG experimental facility, which consists of
1500
100
200_ T _
20
250 +Gap
Drainj - X —
;—T
Level guage
jlnsulatiorjP : pressureT : temperatureUnit: mm
copper shellgap
pressure vessel
Fig. 3. Schematic Diagram of CHFG facility
an electric heater, a pressure vessel, a heat exchanger and acoolant control system. An electric heater is put inside ahemispherical copper shell, which provides the maximumaverage heat flux of 90 kW/m2 at the outer surface. Thethickness and outer diameter of the copper shell are 25 and498 mm, respectively. Four units of stainless steel pressurevessel were manufactured to provide gap sizes of 0.5, 1.0,2.0 and 5.0 mm between the copper shell and the pressurevessel itself. The experiments were performed usingde-mineralized water. The measurements of critical powerwere made in the range of 1 to 10 atm. The heat generatedby the electric heater is removed in a heat exchangerinstalled 150 cm above the top of the pressure vessel tomaintain a near-saturated condition of the working fluid.The heat exchanger takes a role in system pressure regu-lation as well. A level gauge is installed in the pressurevessel to confirm that the heater is always covered withwater during the experiments. The occurrence of dryout isnoticed by 66 K-type thermocouple readings. The ther-mocouples are embedded in the copper shell, as shown inFig. 4. From each pair of T/Cs, local heat flux is calculatedand found to be within a ±20% variation of average in anucleate boiling regime. The temperatures and mass flowrates are processed by a Hewlett Packard data acquisitionsystem and HP-VEE program.
As the experimental facility constitutes a closed loop,the first step necessary to carry out experiments is to purgethe air accumulated in the loop. If the air remains in theloop, it obstructs the heat transfer in the heat exchanger sothat the working fluid might not circulate. Initially theheater power is maintained at a low level and the set-valueof the pressure control system is set at a pre-determinedvalue. All the temperature readings are displayed graphi-cally on a computer monitor and carefully observed. If the
- 85 -
45
outside (5-8,21-24) outside Fig. 4. Thermocouple locations
temperature readings are believed to reach a quasi-steadystate, the heater power is increased step-wisely. When allthe temperature readings increase monotonically without alimit, the heater power is cut off. Usually it took 15 to 30minutes to reach a quasi-steady state in a low power rangeand more than 60 minutes near the critical power.
Results and discussionsFigures 5 and 6 show the temperature measurements madeat a gap size of 2 mm and atmospheric pressure. Those areprojections of the hemispherical surface of the coppershell. The boundary and the center of the circular arearefer to top end of the gap and the lowest bottom of thecopper shell, respectively. Small circles shown in radialdirections represent thermocouple locations. The readingsfrom those thermocouples are interpolated to give iso-thermal lines. Figures 5a-d show temperature variationmeasured at heat fluxes of 32, 42, 52 and 60 kW/m2, re-spectively. Through the present paper, heat flux refers tothe average heat flux over the whole outer surface of thecopper shell. Temperatures of the heater and copper shellreached a quasi-steady state after 15 ~ 30 minutes sincethe heater power changed. Quasi-steady state values wereused to make these plots. The surface temperature wasquite uniform up to a heat flux of 32 kW/m . At a heat fluxof 42 kW/m2, heat-up started from around the upper leftedge. This high temperature region expands toward both
the azimuthal and downward directions with an increasein heat flux. Considering the visual observations of VISU-II experiments, this indicates that a local dryout regiondevelops and expands with an increase in heat flux. At aquasi-steady state corresponding to each heat flux, thelocal dryout region continues to exist with just a littlemovement of its boundary. In the VISU-II experiment, itwas observed that the interface between wet and dryoutregion fluctuated in a distance of several centimeters whilethe majority area of dryout region remained out of contactwith water. A similar situation was observed in the CHFGtest The temperature readings started to fluctuate in arange of 5 °C just before they jumped up from nearlysaturated values to much higher values. The fluctuationlasted for a while but no more fluctuation was observedafter the temperature reached a high value. During atransient period caused by an increase in heater power, thedryout region expands and its front passes the locationswhere thermocouples are embedded. When the frontpasses a thermocouple, it is believed, the dryout frontfluctuation causes the temperature fluctuation. The dis-tinguishably higher temperature region, than the saturatedvalue, is regarded as a dryout region in the CHFG test eventhough the temperature does not exceed the minimum filmboiling temperature for a pool boiling condition. Whalley[15] said the minimum film boiling temperature of waterat 1 bar is around 290 °C. It can be seen from Fig. 5 thatthe temperature of the isotherm line-crowded region is
- 86 -
Fig. 5a-d. Temperature variation. Gapsize: 2 mm; Avg. q" (kW/m2); a 32. b 42;c 52; d 60
Fig. 6a-d. Self-expansion of dryout Gapsize: 2 mm; Elapsed time at q" = 68 kW/m2.a 0; b 500; c 1400; d 1600
- 87 -
below 290 °C. The temperature of the surface remainedbelow 290 °C until the whole surface dried off as can beseen in Fig. 6. The conduction through the copper shelland the heater itself of the CHFG rig seems to cause thetemperature of such a stable dryout region to remain be-low 290 °C. That is, the remaining heat that was not re-moved in the local dryout region, moves to the wettedregion by conduction to be removed. Another noticeablepoint is the non-contact of water with the dryout region.The temperature of the isotherm line-crowded region(dryout region) corresponds to a transient boiling regimeof a pool boiling curve. It is believed however that water isnever in contact with the surface of the dryout region whileit is in a quasi-steady state because there was no sign ofwater contact like a sudden temperature decrease orfluctuation. It seems that the hydrodynamic characteristicsin a hemispherical narrow gap, which are different fromthose of a pool boiling case, caused the non-contact at thetemperature corresponding to transient boiling regime ofa pool boiling case.
The high temperature region always started from theupper left edge. The reason for this is speculated to bebecause the gap size around this area is smaller comparedwith the other region. Although the curved components ofthe facility were machined using a CNC machine, the gapsize can be slightly non-uniform because of miss-align-ment or thermal expansion. The measurements of actualgap sizes by the ultra-sonic technique (UT) under thesame condition as the experiments showed that the devi-ation in gap sizes from the design value was within theinstrument's inherent error. It can therefore be said thatthe gap size was reasonably uniform.
Figure 6 shows the temperature variation with time inseconds when the heat flux was fixed at 68 kW/m2. Tem-peratures over the whole surface increase by itself, eventhough the heater power is maintained at a fixed level. Thismeans there is no steady state at this heat flux, which is adifferent situation from that shown in Fig. 5. In the lowerpart of Fig. 6a, there is a large area without isotherm lines.The temperature of this region remains slightly higherthan 100 °C and the area keeps shrinking with time. Thatis, the wetted region shrinks and the dryout region ex-pands with time. The velocity of the dryout expansion andtemperature increase rate of the dryout region get largerwith time. This is because the local heat flux at the wettedregion increases due to extra heat transferred from thedryout region by conduction. When the dryout regionexpands to the bottom of the copper shell, the temperatureincrease of that location is so fast that the heater powershould cut off immediately for higher protection. We de-fined this heat flux with which the dryout region under-goes self-expansion as the critical power in the geometry ofhemispherical narrow gaps.
The present definition of critical power is different fromthe usual definition of CHF used in other experiments. Ifexperiments are carried out with a specimen like a thinplate, pipe and wire, the temperature jumps quickly assoon as the boiling regime turns into a stable film boilingbecause the heat capacity of the specimen is small. Theheat flux at this situation is usually defined as the CHF.However, if the heat capacity of the heated section is large
enough, such as the present facility (copper 200 kg), thetemperature increases slowly because it needs a lot of heatto be heated up. Even in the local dryout region, thetemperature increases slowly and it is limited. This is be-cause the remaining heat which was not removed in thelocal dryout region, moves to the wetted region to be re-moved. Some experimental results related to such a heatermass (thickness) effect on the maximum pool boiling heatflux are available in the literature. Peyayopanakul andWestwater [16] reported that for test sections of coppercylinders >25 mm in thickness, maximum heat flux wasindependent of wall thickness and the pool boiling curveswere all quasi-steady state and equivalent to those ob-tained in steady-state tests. Depending on the thickness,the quenching time varied from 7 hr to 2 min in theirexperiments. El-Genk and Glebov [17] employed down-ward-facing curved copper sections to test the effect of testsection thickness. Their results showed that the maximumboiling heat fluxes were independent of wall thickness>19 mm. In the present facility, the thickness of coppershell only is 25 mm. Considering the fact that a heaterblock is situated inside the copper shell, the present heatedsection is believed to be thick enough. The reason that theoccurrence of local dryout is not chosen as a critical valuelike a usual CHF in the present experiments is as follows:(i) The present experimental facility does not allow thevisual observation of the flow pattern, and it is thereforehard to tell whether the flow is in a stable film boilingregime only with temperature readings, (ii) The occur-rence of local dryout is induced by CCFL phenomena,which is highly dependent on the geometry of the testsection. Therefore global parameters rather than local onesseem to be better to characterize the boiling behaviour,(iii) Even though local dryout occurs, all the generatedheat finally cools down due to conduction, as mentionedbefore. Therefore the temperature does not increase mo-notonously but is limited by a certain value. However,above a certain heat flux, temperature increases continue.It is therefore reasonable in the present geometry thatcritical power should be defined as the heat flux whichexceeds the maximum cooling capacity through a hemi-spherical gap so the dryout region undergoes self-expan-sion and leads to a global dryout
Figure 7 shows the temperature variation at criticalpower under atmospheric pressure and the gap size is1 mm. The global dryout occurred at the heat flux of60.3 kW/m2, which is lower than that measured with a gapsize of 2 mm. The local dryout started to develop at thesame location as the case where the gap size is 2 mm.When the gap size was 1 mm, the dryout region expandsfaster in the azimuthal than downward direction. As canbe seen in Fig. 7c, the bottom surface is still wet althoughthe top end of the gap is dried off. In Fig. 7d, the dryoutregion finally expands to the bottom and the temperatureover the whole surface increases to over 200 °C.
The predictions by Chang & Yao [10] and Monde et al.[ll]'s CHF correlations, Eqs. (1) and (2), are comparedwith the present measurements in Fig. 8. For comparison,we put the parameters of the present experiments into theabove correlations and the gap size was assumed to be1 mm. Koizumi et al. [18]'s CCFL measurements are also
- 88 -
Fig. 7a-d. Self-expansion of dryout. Gapsize: 1 mm; Elapsed time at q" = 60.3 kW/m2. a 0. b 1000. c 1500. d 2500
compared. They carried out CCFL experiments in narrow-gap annular passages and presented their experimentaldata. The inner diameter of the outer pipe of the facilitywas 100 mm. Various sizes of the inner pipe were used tomake the gaps of 0.5, 1.0, 2.0 and 5.0 mm. Since they didnot suggest any CCFL correlation, we did some regressionanalysis to develop the following CCFL correlations:
; ' 1 / 2 + 0.23;*1/2 = 0.32 for 2 mm gap
jl1/2 + 0.35;f1/2 = 0.35 for 1 mm gap
where, jl = •
(3)
(4)
250,
200 \
" I 150
X 100
o
50
2 mm1 mm0.5 mmChang & YaoMonde et al.Koizumi(1 mm)Koizumi(2 mm)
20 40 60 80Pressure(psia)
100 120
Fig. 8. Comparison of measurements with existing correlations
In order to present them in Fig. 8, superficial velocitiesare changed into corresponding heat flux that can producethe same mass flow of steam. Koizumi et al.'s CCFL cor-relation seems to be close to the present measurements interms of value and pressure trend, while Chang & Yao andMonde et al.'s correlations predict much higher figures.The reason is thought to be that, in the present experi-ments, CCFL prevents water from penetrating into the topend of the gap and global dryout occurred at lower heatfluxes. Compared with those two empirical CHF correla-tions, the pressure effect of the present results seems to bequite small. As those two CHF correlations were developedbased on the data measured under atmospheric pressure,the pressure trend predicted by them might not be correctEspecially, Monde et al. [ll]'s correlation shows monot-onous and rapid increase in CHF with system pressure. Itdoes not seem to be appropriate to use Eq. (2) at an ele-vated pressure. The gap size effect on critical power inhemispherical narrow gaps is also shown in Fig. 8. Theincrease in gap size from 0.5 mm to 1 mm almost doublesthe critical power but that from 1 mm to 2 mm affectscritical power just a little. The measurements with the gapsize of 2 mm were only made at atmospheric pressurebecause of the lack of heater capacity. Further works areneeded to quantify the effect of gap size on the criticalpower.
Concluding remarksStudies on boiling heat transfer experiments in hemi-spherical narrow gaps and visualization experiments in the
- 89 -
same geometrical shape have been done, respectively.According to visual observations, CCFL occurs at the topend of the gap and prevents water from penetrating thegap. That is, it can be said that a CCFL brings about localdryout and finally, global dryout in hemispherical narrowgaps. Even if local dryout occurs, there exists a quasi-steady state and the temperature of the dryout region islimited with a certain value. When the heater power islarge enough, however, there is no quasi-steady state. Thedryout region expands by itself without an increase inheater power, finally leads to a global dryout, and thetemperature of the heater surface monotonically increases.The heat flux bringing about that situation is defined asthe critical power in the present experiments. The exper-iments using water were completed. Measured values ofcritical power are much lower than the predictions madeby empirical CHF correlations applicable to flat plate gapsand annuli. The pressure effect on the critical power wasfound to be much milder than predictions by those CHFcorrelations. The values and the pressure trend of thecritical powers measured in the present experiments areclose to the values converted from the CCFL data. Thisconfirms the claim that a CCFL brings about local dryoutand finally, global dryout in hemispherical narrow gaps.
References1. Rempe JL; Wolf JR; Chavez SA; Condie KG; Hagrman DL;
Carmack WJ Investigation of the coolability of a continuousmass of relocated debris to a water-filled lower plenum.EG&G Idaho Report, EGG-RAAM-11145, 1994
2. Henry RE, Dube DA Water in the RPV: a mechanism forcooling debris in the RPV lower head, OECD-CSNI specialistsmeeting on accident management. Sweden, 1994
3. Maruyama Y; Yamano Nj Sugimoto J In-vessel debris cool-ability experiments in ALPHA Program. Proc Int Top Mtg onPSA'96, Park City, Utah, 1996
4. Henry RE; Hammersley RJ An Experimental Investigation ofPossible In-Vessel Cooling Mechanisms. CSARP Meeting,Bethesda, Maryland, 1997
5. Rang KH; Kim JH; Kim SB; Hong JH; Kim HD Experimentalinvestigations on in-vessel debris coolability through inher-
ent cooling mechanisms, OECD/CSNI WS on in-vessel coredebris retention and coolability. Garching, Germany, 1998
6. Mayinger F; Homer P; Zeisberger A Information about ac-tual research activities on: Debris/Reactor pressure vesselinteractions after partial core melting. CSNI special meetingon on-vessel debris coolability and lower head integrity, 1996
7. Kohler W; Schmidt H; Herbst O; Kratzer W Experiments onheat removal in a gap between debris crust and RPV wall,OECD/CSNI WS on in-vessel core debris retention andcoolability. Garching, Germany, 1998
8. Sudo Y; Kaminaga M (1989) A CHF characteristic fordownward flow in a narrow vertical rectangular channelheated from both sides. Int J Multiphase Flow 15: 755-766
9. Katto Y; Kosho Y (1979) Critical heat flux of saturated nat-ural convection boiling in a space bounded by two horizontalco-axial disks and heated from below. Int J Multiphase Flow5: 219-224
10. Chang Y; Yao S (1983) Critical heat flux of narrow verticalannuli with closed bottoms. J Heat Transfer 105: 192-195
11. Monde M; Kusuda H; Uehara H (1982) Critical heat transferduring natural convective boiling in vertical rectangularchannels submerged in saturated liquid. J Heat Transfer 104:300-303
12. Suh KY; Henry RE (1996) Debris interactions in reactorvessel lower plena during a severe accident I. Predictivemodel. Nuclear Eng & Des 166: 147-163
13. Kutateladze SS Heat transfer in condensation and boiling.USAEC Rep-tr 3770, 1952
14. Jeong JH; No HC (1996) Experimental study of the effect ofpipe length and pipe-end geometry on flooding. Int J Mul-tiphase Flow 22: 499-514
15. Whalley PB Boiling, Condensation and Gas-Liquid Flow.Oxford, U.K., Oxford University Press, 1987
16. Peyayopanakul W; Westwater JW (1978) Evaluation of theunsteady-state quenching method for determining boilingcurves. Int J Heat Mass Transfer 21: 1437-1445
17. El-Genk MS; Glebov AG (1995) Transient pool boiling fromdownward-facing curved surfaces. Int. J. Heat Mass Transfer38: 2209-2224
18. Koizumi Y; Nishida H; Ohtake H; Miyashita T (1997)Gravitational water penetration into narrow-gap annularflow passages with upward gas flow. Proc NURETH-8 1:48-52
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KAERI/TR-1321/99
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BIBLIOGRAPHIC INFORMATION SHEET
Performing Org.Report No.
Sponsoring Org.Report No.
Standard Report No. INIS Subject Code
KAERI/TR- 1321/99
Title/Subtitle
A Study on Critical Heat Flux in Gap
Project Manager (or mainauthor)
And Department
Rae-Joon Park(Thermal Hydraulic Safety Research Team)
Researcher andDepartment
Ji-Whan Jeong(Chunan Foreign College),
Young-Ro Cho, Young-Cho Chang, Kyung-Ho Kang, Jong-Whan Kim, Sang-Baik Kim,
and Hee-Dong Kim (Thermal Hydraulic Safety Research Team)
PublicationPlace
Taejon Publisher KAERI PublicationDate
1999. 4
Page p. 102 Fig. & Tab Yes( O ), No( Size A4
Note '98 Nuclear Mid-Long Term Project
Classified Open(O ), Restricted(Class Document Report Type Technical Report
Sponsoring Org. Contract No.
Abstract( 15-20 Lines)
The scope and content of this study is to perform the test on critical heat flux in hemispherical narrow gaps
using distilled water and Freon R-113 as experimental parameters, such as system pressure from 1 to 10 atm and
gap thickness of 0.5,1.0, 2.0, and 5.0 mm. The CHFG test results have shown that the measured values of critical
power are much lower than the predictions made by empirical CHF correlations applicable to flat plate gaps and
annuli. The pressure effect on the critical power was found to be much milder than predictions by those CHF
correlations. The values and the pressure trend of the critical powers measured in the present experiments are
close to the values converted from the CCFL data. This confirms the claim that a CCFL brings about local
dryout and finally, global dryout in hemispherical narrow gaps. Increases in the gap thickness lead to increase in
critical power. The measured critical power using R-113 in hemispherical narrow gaps are 60 % lower than that
using water due to the lower boiling point, which is different from the pool boiling condition. The CCFL(Counter
Counter Flow Limit) test facility was constructed and the test is being performed to estimate the CCFL
phenomena and to evaluate the CHFG test results on critical power in hemispherical narrow gaps.
Subject Keywords(About 10 words)
Gap, Critical Heat Flux, Critical Power, Counter Current Flow Limit, Boiling Heat
Transfer, Two-Phase Flow, Dryout Region
