ML20062H261

A Criterion for the Onset of Quench for LOW Flow Reflood

ML20062H261
Person / Time
Issue date:	07/31/1982
From:	Hsu Y, Matt Young NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES)
To:
References
NUREG-0915, NUREG-915, NUDOCS 8208130477
Download: ML20062H261 (31)

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{{#Wiki_filter:- l NUREG-0915 A Criterion for the Onset of Quench for Low Flow Reflood U.S. Nuclear Regulatory Commission Office of Nuclear Regulatory Research Y. Y. Hsu, M. W. Young r anc, o ,o fx L .i RERSASRef 2 7 0915 R PDR

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NUREG-0915 I A Criterion for the Onset of ' Quench for Low Flow Reflood Manuscript Completed: July 1981 Date Published: July 1982 Y. Y. Hsu, M. W. Young 1 Division of Accident Evaluation Office of Nuclear Regulatory Research U.S. Nuclear Regulatory Commission Washington, D.C. 20555 f, / 's l

ABSTRACT i This study provides a criterion for the onset of quench for low flow reflood. The criterion is a combination of two conditions: Tclad < Tlimiting quench, and (T= Temperature) i a < 0.95 (a = Void Fraction) This criterion was obtained by examining temperature data from tests simulating PWR reflood, such as FLECHT, THTF, P8F, CCTF, and FEBA tests, with void fraction data from CCTF, FEBA, and FLECHT low flood tests. The data show that quenching 4 initiated at a = 0.95 and that the majority of quench occurred at void fractions near 0.85. The results show that rods can be completely quenched by entrained droplets even if the collapsed liquid level does not advance. A thorough dis-cussion of the analysis which support this quench criterion is given in the text of this report. l l l l l l I f iii i 6--t-y.ww-rgwp--- -,y---,n, f -w--.., ,----.------.-,---.--e mwm r -e t-q, m-, m o.<.ww,

1 l l l TABLE OF CONTENTS P_agg ABSTRACT.................. jjj 1 LIST OF FIGURES.......................................................... vi LIST OF TABLES.......................... yjj

1. 0 BACKGROUND.....................................................

1 2.0 ANALYSIS AND DISCUSSION.................. 6

3.0 CONCLUSION

S... 18

4.0 REFERENCES

19 APPENDIX.... A-1 A.1 PROCEDURE FOR DETERMINING QUENCH V0ID........................... A-2 i V

i LIST OF FIGURES Figure Page 1. Comparison of Modified Berenson and Henry Correlations with Data... 2 Recommendation Modification of Iloeje's Correlation for T. 2a. HighMassFlow...........................................?2".at 4 RecommendedModificationofIloeje'sCorrelationforT}.LowTemperature............... 4 2b. at 3. Effect of Mass Flux on Boiling Curves of Distilled Water, Short Block Series for ATSUB = 0 C....................................... 5 4. LocalCoolantandCladTemperature(Run0183FL(illi)During Reflood............................................................ 7 Sa. Statistical Distribution of Quench Void for FLECHT Skew Series, o =.15............................................................ 8 Sb. Statistical Distribution of Quench Void for FLECHT Skew Series, j o =.21............................................................ 9 6. Residence Time of Water at High Frequency Probes................... 10 7. Typical Bubble Plot from Liquid Level Detector Data................ 12 8. Quenching Elevation Profile and Iso-Void Profiles.................. 13 9a. Function B as Function of Vapor Velocity in Covering Typical Range of Conditions................................................ 14 9b. Void Fraction in Froth Layer as Function of B&K from Yeh's Eq...... 15 vi I

LIST OF TABLES Table P_ag 1. B as Function of Vapor Veloci ty and Pressure....................... 16 l 2. Void Fraction as Function of B and K from Yeh's Equation........... 17 l I i ( Vii

i

1. 0 BACKGROUND 4

Existing quench criteria specify a critical temperature, below which quenching is supposed to occur. This temperature has been referred to as: rewet tempera-ture, Leidenfrost temperature, minimum delta-T, etc. In this paper, the quench temperature refers to the " knee" of the clad temperature history when the clad temperature takes its precipitous drop. Strictly speaking, rapid cooling of a rod means that heat dissipation is much faster than heat generation. Since heat generation during reflood is low, the increase of heat dissipation is more responsible for increased cooling. Increased heat dissipation could arise from initiation of transition boiling corresponding to a decrease of the temperature difference (T -Tsat) r surface caused by the arrival of more liquid, (i.e., decrease of quality or void), or both. Whenthereissufficientliquid,,(h)controlscla,dtemperature. When there is a scarcity of liquid, horhiscontrolling. The former case is for high flow bottom reflood, whereas the latter case is for low flow bottom reflood; or for quench due to spray. A general approach to describing the heat transfer surface is to construct a multidimensional surface of q (X, G, P, AT,... ). A rapid drop of clad temperature would occur if heat dissipa-tion increases rapidly along an operating path. Most studies until recently addressed the problem of q(AT), with an attempt to determine the lower limit of film boiling or the upper limit of temperature at which liquid can still physically be in contact with solid. Many models have been proposed. These models are based upon heat conduction (e.g., Thompson's Model Ref. 1), upon the hydrodynamic instability limit (e.g., Berenson's Model Ref. 2), upon the thermodynamic instability limitation (e.g., Spiegler Model Ref. 3), or upon combinations (e.g., Henry Model Ref. 4). The review of the various models can be found in Ref. 5. Figure 1 shows the comparison of the various models with quench data from tests in simulated fuel rod bundles. The data shown are the upper limit of quench temperatures (Ref. 6-10, 14, 17). It should be noted that all these data are from thermocouple readings. No corrections were made for.the radial or axial gradient of heat transfer near the solid-liquid interface. For transient conduction of heat to the surface and a rapid change of heat transfer coefficient, the radial gradient near the solid-liquid interface (" skin") can be particularly significant. Upon instan-taneous contact between the liquid and the solid, the skin temperature may drop to the limiting liquid temperature momentarily while the solid interior temperature may be much higher than the limiting liquid temperature. Henry obtained the empirical Equation 1 to predict the liquid limiting temperature, T L L = (T )* + [(T )* - T ] (0.42) [ C T L g b p L )B AT 1 i i

1800 iiii i i i ig i i ,,i, J / / /g l O FLECHT DATA (WCAP 7435) o THTF 1600 I O FLECHT DATA (WCAP 8651) + p3p 4 D i o G.E. NEDO-20975 4Y,b O ~ x FEBA O 1400 l / h 0I genay W'2 o 3 c,- 1200 / o' o s /' e e g iOOO - - - - e 3 g- - gn, tssA / - e-e-C / h U f Oa o / j @9/ ,g tas0" - f 6 9 g8 f#,/.o / + 900 F 0 600 ,e 400 / 6 200 0 10 10 0 1000 PRESSURE, psi Figure 1. Comparison of Modified Berenson and Henry Correlations with Data l l 2

InHenry'sequation,T{istheBerensen'sminimum-aTtemperaturebasedupon hydrodynamic instability considerations. T{iscontrollinginthelowpressure rangewhere[I is large. Forhighpressures,T{shouldbesetasalimitation of the liquid state based upon thermodynamic considerations with the classical form being T. The upper limit of quench temperatures shown in Figure 1 are C higher than either the thermodynamic limit or the hydrodynamic limit. It is even higher than Henry's limiting temperature, possibly because of the additional temperature drop across the gap around the sheath of the thermocouple. Since gap resistence is difficult to define when the rod is undergoing a temperature change and since the dependence of the limiting quench temperature or flow condition is unknown, one tentative solution is to set T = 1000 F, pending limit formulation of a complete quench model. It is very interesting to note that no quench criteria except Iloje's Eq., have considered the effect of flow on quench. This oversight might be due to the fact that earlier models were formulated for pool boiling. To account for the flow condition, Iloje's equation for quench (Equation 2 subject to modifi-cation in Fig. 2) (Ref. 11) was selected by the Rewet Workshop (Reference 12). = 0.29 [1 - 0.295 X 2.45] [1 + (G x 10 4)0 M ] Eq. 2 88 (L -Tsat)Berenson Iloeje's equation shows that quench temperature is a function of flow rate, inlet subcooling, and pressure. The positive dependence of quench on pressure is not surprising. However, the parametric dependency of quench on flow rate G has not been very clear (see Figure 3 for flat profile, Ref. 13). As to subcooling effects, it is difficult to visualize that a quenching process, which is a local phenoniena, would depend upon inlet subcooling, which loses its meaning as liquid progresses into the bundle. 3

- - - Rscommanded fix g el'60 cog gioch", min j / / s / / / / e t e m 100,000 2 C (1b/ft -hr) Figure 2a. Recommendation Modification of Iloeje's correlation for T at high mass flow (Ref. 12) min _ _ Recorr:: ended Fix / Q*s\\' / / / / /

nin

/ s' r-- Te / N enry's recom:nendation H o c / / / P Figure 2b. Recommended modification of Iloeje's Correlation for T at low pressure (Ref. 12) min 4

I i i i i i I i i a i 1 I TRANSIENT RUNS INITIAL TEST SECTION AT MEAN TEMP. : 4 2 6.6' C PLANE 8 2 o RUN 514 G = 6 8 k g/m s o 2 o RUN 506 G = 136 kg/m 3 2 0 RUN 515 G:203 kg/m s 10 7 o r o n 7 N / o O E N o o u ( } b g s '^ " O o o o y G G v s a y b a' ti h) LJ I 5 10 r k i I i i I i 1 I i I I i 11 0 15 0 19 0 230 270 310 350 WALL TEl!.PERATURE (*C) Figure 3. Effect of Mass Flux on Boiling Curves of Distilled Water, Short Block Series for ATSUB = 0 C @ef. 12) 5

2.0 ANALYSIS AND DISCUSSION To reexamine the problem of quenching, it is important to remember that for quenching to occur, two conditions must be satisfied simultaneously; namely, that the clad temperature must be low enough for liquid to make the momentary contacts and that liquid must be present. Clad temperature can simply decrease to any low temperature by precursory cooling before its precipitous drop upon arrival of liquid (see Figure 4). Thus, correlations such as Iloje's equation, which do not consider the effect of void, could predict quench temperatures in i error by several hundred degrees. The conservative approach of setting the lower bound of the data as a criterion for quench temperature is not realistic since the lower bound refers to the temperature when water arrives and can be arbitrarily set to a lower level by holding back the water. The above argument shows the absurdity of using quench temperature as the sole criterion without consideration of the need of liquid for cooling. On the other hand, it is important to understand that with the quench temperature criterion met, quench-ing is possible even though the " solid" water reflood front has not reached the quench elevation, i.e., 100% carryover. Entrained droplets which travel from the reflood elevation up through the voided channel serve to decrease void fraction and satisfy the void fraction criterion for quenching. The presence of water can be represented by the water fraction, at, which is 1-a, with a being the void fraction. The local void fraction can be determined from local impedance probes at quench elevations, or to a lesser degree of accuracy, from local dp measurements of collapsed static liquid level of each cell. The void fractions at the quench elevation obtained from interpolation of dp-data of FLECHT tests are shown in Figure 5. As shown, for the data from tests with a low flooding rate, 70 percent of the quenching takes place at void fractions between 0.70 and 0.95 (.70<a<.95). The quenching criteria of 0.70<a<0.95 is verified by FEBA data (Ref. 14), as shown in Figure 6. As shown below, six data points were available for the quench void, a, measured from the time-fraction of dry conditions as measured q by local impedance probes. The void fraction at quenching is obtained from the relationship; a=t dry /(tdry + twet), averaged over 10 sec intervals, i where t is the time at the dry or wet condition. l Run No. 177 182 Elevation HF1 HF2 HF3 HF1 HF2 HF3 a 0.92 0.93 0.96 0.88 0.75 0.93 q For present PWR designs, quench is due to bottom reflood alone and the quench front was observed to be coincident with the advance of the froth front (which is much higher than the collapsed liquid level) as shown in FLECHT tests (Ref. 15). Then, the quench void fraction is nothing more than the void fraction at the froth front. In some reflood tests, however, the rod is quenched from both top and bottom by cooling from spray or entrained liquid. I I i 6 l l

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=

+ +_- w Void Fig 5-B: Statistical Distribution of Quench Void for FLECHT Skew Series i 9

M .i W 9 100 1 n ~ / <3 / integration time 10 s steDS 3 h / run no.177 (206) w 80 - / 2 v = 2 cm/s [ [/ v p = 4.5 ba r i:- h 60 - /

{

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t u-M IRB Figure 6.

Residence Time of Water at High Frequency Probes (Ref. 14)

In such a case the quench front movement is different from the water front movement. For example, in some large multibundle tests, the water level did not advance beyond 1/3 of the core until after the core was completely quenched. Consequently, there is a need to define a quench void as a quench criterion. Fig. 7 shows the typical " bubble plots" of liquid level indicators in a proprietary test. If one takes 10 sec intervals and equates the time fraction of the " dry" condition to the void fraction, the bubble plots at various elevations can be converted into " Iso-void" profiles as shown in Fig. 8 (in the form of elevation vs. time). Also shown in the same figure are the profiles of quench fronts. Note that, the liquid level (a = 0.1) hardly advanced for most of the reflood period, while the quench front is enveloped by profiles of 0.75 < a < 0.95. A further confirmation of the proposed void-fraction criterion is from the FLECHT Data Analysis Report (Ref. 16), in which it was shown that the quench front is very close to the froth front. The void fraction of the froth front can be calculated to be in the range of 0.70 to 0.99 as shown in Figure 9 and the Appendix. Figure 9 was based on Yeh's equation, using the parameter K in that equation in the range of 0.'01 to 0.001, whicli is the predominant range for low-flooding rate data. The parameter B in the same equation is a function of pressure and velocity. Figure 9a covers the range of B expected from FLECHT low-flooding tests. Figure 9b shows that for the range of B covered, the void fraction of the froth is 0.70 to 0.99 (Table 1, 2). However, since the void fraction of the froth changed rapidly with elevation and a = 0.99 requires an accurate prediction of void fraction, the upper rewet void fraction is set to be 0.95 as a more reliably predicted value.

Thus, quench < 0.95.

Eq. 2 0.70 < a 11

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I+ ( e-Figure 9b. Void Fraction in Froth Layer as function of B + K From Yeh's Eq. 15

Table 1 B as function of Vapor Velocity and Pressure Ppsi Vgi, 20 40 60 ft/sec. 6 0.667 0.79 0.87 9 0.806 0.955 1.05 12 0.920 1.09 1.20 15 1.025 1.21 1.34 18 1.12 1.32 1.46 0.239 V a=0.925([p) [1+k] 0.6 = B [1+k] 0.6 U y 1 bcr K= f = f" (1-ajj g i i l V B = 0.925 ( ) 0.239 (y oi ) 0.47 bcr bcr 9 "bcr [ 4' 9 ]2 yo R = g 999 From Yeh's Equation in Ref. 16 16

Table 2 Void fraction as function of B and K from Yeh's equation (Ref. 16) B= 0.34 0.79 0.81 0.87 0.92 0.96 1.0 1.1 1.2 1.3

1. 5 K=0.01 a=

0.34 0.77 0.79 0.839 0.88 0.904 0.926 0.9606 0.976 0.983 0.990 K=0.003 a= 0.84 0.78 0.859 0.965 0.959 0.985 0.992 0.9946 0.997 K=0.001 a= 0.34 0.788 0.866 0.949 0.976 0.995 0.9972 0.9982 0.999 C

-=

3.0 CONCLUSION

From THTF, FLECHT, PBF, FEBA, GE, CCTF data, the limiting quench temperature is found to be 1000*F. From FLECHT, CCTF, and FEBA, the quenching void i criterion is found to be: l a < 0.95 The above two conditions for limiting quench temperature and quenching void l fraction must be satisfied simultaneously for quenching to occur. A procedure for application of the above criteria is given in the Appendix. l The implications of a quench void criterion are twofold: 1. Quench temperature alone is not sufficient to determine whether the rod is going to be quenched. j 2. Even for the case of 95-100% carryover, i.e., when the collapsed water level does not advance or only advances very ' slowly, the entrained droplets, with flow void less than 0.95, can quench the rods, provided the rod temperature is below the limiting quench value (say 1000 F). l 4 i I i i l 1 18

- = _. - - _ - ~ = i

4.0 REFERENCES

1. Thompson, T. S., "An Analysis of the West-Side Heat Transfer Coefficient During Rewetting of a Hot Dry Patch," Nucl. Eng. & Design 22, pp. 212-224 (1972). 2. Berenson, P. J., " Film Boiling Heat Transfer from a Horizontal Surface," Journal of Heat Transfer 83, pp. 351-358 (1961). 3. Spiegler, P., Hopenfeld, J., Silberberg, M., Bumpus, C. F., and Norman, A., " Onset of Stable Film Boiling and Foam Limit," Int. Journel Heat Mass Transfer 9, pp. 1219-1226 (1966). 4. Yao, S. and Henry, R. E., "An Investigation of the Minimum Film Boiling Temperature on Horizontal Surface," Journel of Heat Transfer 100, (2), pp. 260-267 (1378). 5. Chen, W. L., "A Study of Rewet Phenomenon," ANL-RAS-LWR-80-4, Argonne National Laboratory, October 1980. 6. Rosal, E. R., et al., "FLECHT Low Flooding Rate Cosine Test Series Data Report," WCAP-8651, NRC-Westinghouse Cocperative Research and Development Report, December 1975. 7. Rosal, E. R., et al., "FLECHT Low Flooding Rate Skewed Test Series Data Report," WCAP-1908, NRC-Westinghouse-Electric Power Research Institute Cooperative Research and Development Report, May 1977. 8. E. Janssen and J. A. Kervinen, " Film Boiling and Rewetting," NEDO-20975 (1975). t 9. Thomas, D. G., Progress Report on Return to Nuclear Boiling, " Electrically Heated Rod Bundles Under Simulated PWR Elevation Conditions," ORNL, Presented in NRC Denver Workshop on Rewet, Denver, CO., April 1977. 10. Yackle, T. R., "An Assessment of the Influence of Surface Thermocouples on the behavior of Nuclear Fuel Rods during a large Break LOCA," EG&G, Inc. presentation at 8th WRSR Information Meeting, Gaithersburg, Md. Oct. 1980. i 11. Iloeje, O. C., Plummer, D. N., Rohsenow, W. M., Grif fith P., "An Investiga-tion of the Collapse and Surface Rewet in Film Boiling in Forced Verticle Flow," Journal of Heat Transfer, 97, pp.166-172 (1975). 12. Hsu, Y. Y. and Loren Thompson, " Meeting minutes of Denver workshop on Rewet," NRC Memo, May 15, 1971. 13. Cheng, S. C., N.G., W.W.L., Heng, K. T., and Groenveld, D. C., " Measurements of Transition Boiling Data for Water Under Forced Convective Conditions," Journal of Heat Transfer, 100, pp. 382-384 (1978). 19

l 14. Hirano, K., et al. " Quick-Look Report on largo Scale Reflood Test 9 CCTF Test Cl-9 (Run 018)," Japanese Atomic Energy Research Instotite-memo 9125, Sept. 1980. 15. G. P. Lilly, et al., "PWR FLECHT Cosine Low Flooding Rate Test Series Evaluation Report," WCAP-8838, NRC-Westinghouse-Electric Power Research Institute Cooperative Research and Development Report, March 1977. 16. J. O. Cermak, et al., "PWR Full-length Energency Cooling Heat Transfer (FLECHT) Group 1 Test Report," WCAP-7435. Westinghouse Electric Corporation, January 1970. l l I t' l 20 l l l

9 6 APPENDIX QUENCH VOID DETERMINATION A-1

A.1 PROCEDURE FOR DETERMINING QUENCH VOID l 1. Check to see if T -< 1000*F. If T > 1000 F, no quench is allowed. If T,< 1000* F, proEeed to determine

• void.

2. To determine void: a. For quench at the froth front, use a modified Yeh's equation for void fraction: a = B(1 + K) 0.6 B = 0.925 ( ) 0239( )a 1 bcr K = jg/(1-a)j 9

• 2
• E.53 2 1

o 3 bcr 3 9 ^ bc' bc 2/3 gpy a = 0.47 U = j /a g g zquenchq z dz j = g g H pA 7 g zquenchq z dt U =[U A P ~ H 1 g ]/P A E flood c E g Note: The a-equation is implicit since (1 a) appears in K on the right-hand ~ side. It takes iteration to obtain a. When a is close to unity, care must be exercised to avoid numerical oscillation since a has multiple roots and only one is correct. The one root with a>l is not a correct solution. Some of the a curves in terms of B & K are shown in Fig. 9. i A-2

b. For quench by entrained liquid droplets: (Ud+3 + I ) - 4(Ud*dl+d) - 4d U E g g gd 2Ud with jelevatlo&jn. 9IfthereisfallbackfromE8pIhj is a ccmbination of liquid same as before, except Z refers to the bottom quench 9 j from bottom and top. "9(Pb~P)

• (4 We*) E 3

g Ud 3C 2 d pg We* is critical weber number, usually about 10-20, but it may vary with grid space geometry. C is drag coefficient, usually 0.45 d o is surface tension, p and p are densities. j 3. Check to see if a is less than 0.95, If so, quench is initiated. i A-3

U.S. NUCLE AR REGULATORY COMMISSION 87 77) BIBLIOGRAPHIC DATA SHEET NUREG-0915 4 TITLE AN D SUBTsT LE LAdd Voturne No. of warerosent

2. fleeve bleshi A Criterion for the Onset of Quench for Low Flow Reflood

7. AUTHOR (St 5 OATE REPORT COMPLETED M ON T H l YEAR Y. Y. Hsu, M. W. Young July 1981 9 PE RF ORMING ORGANIZATION N AME Af tD M AILING ADDRESS (include I,a Codel DATE REPORT ISSUED U.S. Nuclear Requlatory Commission "oNT" Ivtaa Division of Accident Evaluation July 1982 Office of Nuclear Regulatory Research 6 (L '* * *'*a * >

Washington, DC 20555 8 (Leave Disnk)

12. SPONSORING ORG ANIZ ATION N AME AND M AILING ADDRE SS (Inclu* I,p Code) p U.S. Nuclear Regulatory Commission Division of Accident Evaluation

11. CONTRACT NO.

Office of Nuclear Regulatory Research Washington, DC 20555 13 TYPE OF REPORT PE RIOD COVE RE D (Inclustre dams) Technical

15. SUPPLER /ENT ARY NOTES

14. (Leave craik/

16 ABSTR ACT 000 woras or lessi This study provides a criterion for the onset of quench for low flow reflood. The criterion is a combinat' ion of two conditions: Tclad < Tlimiting quench, and (T= Temperature) a < 0.95 (a= Void Fraction) This criterion was obtained by examining temperature data from tests simulating PWR reflood, such as FLECHT, THTF, PBF, CCTF, and FEBA tests, with void fraction data from CCTF, FEBA, and FLECHT low flood tests. The data show that quenching initiated at a = 0.95 and that the majority of quench occurred at void fractions near 0.85. The results show that rods can be completely quenched by entrained droplets even if the collapsed liquid level does not advance. A thorough dis-cussion of the analysis which supports this quench criterion is given in the text of this report.

17. KEY WORDS AND DOCUMENT ANALYSIS 17a DESCRIPTORS Void Fraction I

Guench Reflood 17b. IDENTIFIERS /OPEN-ENDED TERMS

18. AVAILABILITY STATEMENT

19. SE CURITY CLASS (Tths report)

21. NO. OF P AGE S Uncl assi fied Unlimited

20. SECURITY CplSS (This papel

22. PRICE Unclassified s

hf C FORM 335 (7 77)

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