LOFT Experiment LP-02-6 Analysis by RELAP5/ MOD2 Code with Improved Minimum Film Boiling Temperature

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1 Journal of Nuclear Science and Technology ISSN: (Print) (Online) Journal homepage: LOFT Experiment LP-2-6 Analysis by RELAP5/ MOD2 Code with Improved Minimum Film Boiling Temperature Yasuo KOIZUMI, Yoshinari ANODA, Kanji TASAKA, Yuichi MIMURA & Akio MAEDA To cite this article: Yasuo KOIZUMI, Yoshinari ANODA, Kanji TASAKA, Yuichi MIMURA & Akio MAEDA (1988) LOFT Experiment LP-2-6 Analysis by RELAP5/MOD2 Code with Improved Minimum Film Boiling Temperature, Journal of Nuclear Science and Technology, 25:4, , DOI: 1.18/ To link to this article: Published online: 15 Mar 212. Submit your article to this journal Article views: 177 Citing articles: 1 View citing articles Full Terms & Conditions of access and use can be found at

2 Journal of NUCLEAR SCIENCE and TECHNOLOGY, 25[4), pp (April 1988). 395 TECHNICAL REPORT LOFT Experiment LP-2-6 Analysis by RELAP5/MOD2 Code with Improved Minimum Film Boiling Temperature Yasuo KOIZUMI, Yoshinari ANODA, Kanji TASAKA, japan Atomic Energy Research Institute* Yuichi MIMURA and Akio MAEDA JSL Co.** Received September 7, 1987 Groeneveld-Stewart's minimum film boiling temperature correlation was incorporated into the RELAP5/MOD2 code in order to explicitly define the minimum film boiling temperature. The transition boiling curve in the code was also modified. The Loss-of-Fluid Test (LOFT) experiment, Experiment LP-2-6 which was a cold-leg double-ended break LOCA experiment with minimum emergency core coolant injection, was analyzed with the modified RELAP5/ MOD2 code. The modified RELAP5/MOD2 code well calculated system transients including the rod surface temperature transient. The temporary rewetting of rods in the early phase of blowdown, which had not been predicted by the original RELAP5/MOD2 and other codes, was predicted by the modified RELAP5/MOD2 code. KEYWORDS: LOFT, double-ended break loss of coolant, browdown, ECCS, minimum film boiling temperature, rewet, quench, PWR, PCT, heat transfer, computer codes I. INTRODUCTION Experiment LP-2-6 was conducted on October 3, 1983 in the Loss-of-Fluid Test (LOFT) facility<'l at the Idaho National Engineering Laboratory (INEL). The experiment simulated a pressurized water reactor (PWR) loss-ofcoolant accident (LOCA) caused by a doubleended break of a cold leg. In the experiment, minimum injection from the emergency core coolant system (ECCS) was employed. The experiment was initially planned in the United States Nuclear Regulatory Commission (USNRC) LOFT Program< 2 l_ It was brought over to the Organization-for-Economic-Cooperationand-Development (OECD) LOFT Project and conducted in that project, partially as an experiment in the NRC LOFT Program. The double-ended break LOCA is the most important pipe break considered when licencing a nuclear reactor. Although it is hypothetical, it is a design basis accident. In view of the importance, extraordinary efforts have been made to understand the phenomena associated with a double-ended LOCA. World wide interest has spawned Semiscale experiment<s) and ROSA- IT experiments< 4 l as well as the LOFT experiments. The LOFT facility was a volumetrically scaled (1/44) PWR system with a nuclear core and was designed for integral LOCA/ECCS experiments. Four double-ended cold leg break LOCA experiments were conducted at the LOFT facility, Experiments L2-2, -3,-5 and -6< l. As described in Ref. (5) and (6), a fuel rod surface temperature excursion occurred immediately after break initiation in these experiments, however temporary fuel rod surface rewetting was observed throughout the core, except for Experiment. L2-5 in which the reactor coolant pumps coasted down quickly. * Tokai-mura, Jbaraki-ken ** Funaishikawa, Tokai-mura, Ibaraki-ken

3 396 TECHNICAL REPORT (Y. Koizumi et a/.) ]. Nucl. Sci. Technol., It is postulated that the temporary rewetting was caused by quality fluid insurge into the core. The rewetting could not be calculated by analytical codes as discussed in Refs. (5) and (6). This temporary rewetting is important since it acts to suppress the peak cladding temperature (PCT) during the blowdown or refill/reflood period. This report presents the analytical results of LOFT Experiment LP-2-6 using the RELAP5/MOD2/CY36.2 code(7) focusing on the temporary rewetting. In the analyses, the RELAP5/MOD2 code was improved to explicitly define the minimum film boiling temperature by incorporating Groeneveld-Stewart's minimum film boiling temperature correlation< 8 l. The transition boiling curve was also modified. H. FIRST CALCULATION RESULTS The nodalization is the same as used in Ref. (9) for LOFT Experiment L2-5. The LOFT facility is represented with 128 volumes, 146 junctions and 89 heat slabs including 6 peak power channel volumes and 6 average power channel volumes in the core. The calculated peak power rod surface temperature at the middle of the core is compared with measured ones in Fig. 1. The data show a temperature excursion immediately after the break initiation, temporary rewetting around 7 s at about 7 MPa and a temperature excursion again around 11 s. However, the calculated result does not have the temporary rewetting and the rod surface temperature remains at a high value after the first tern- Time Fig. 1 Comparison of cladding temperatures, measured at mid part of core and calculated with original RELAP5/MOD2/CY36.2 s II perature excursion until the final quenching at about.3 MPa due to core reflood caused by ECCS actuation, as discussed in Refs. (5), (6) and (9). The calculated and measured mass flows in the intact loop hot and cold legs, and broken loop hot and cold legs are compared in Figs. 2(a), (b) and 3(a), (b). The agreement between calculated and measured flows is good, especially until 15 s. Although there was no direct measurement of core flow rate in the. LOFT facility, core flow rate can be estimated from the loop flows. It may be assumed that the core flow rate is properly calculated, especially during temporary rewetting period since the calculated loop flow rates are in good agreement with the measured results. Thus, it may be concluded that the failure of the codes to predict the temporary rewetting in the calculation is not caused by improper calculation of the core flow rate. If that is correct, the reason might be due to the method Jf 2 1 :: LL: -1 Jf :: LL: -1-2 Fig. 2 (a), (b) -- RELAP5 --- Data (a) (b) Time Intact loop hot leg Time s Intact loop cold leg Comparison of intact loop hot and cold legs mass flows, measured and calculated with original RELAP5/MOD2/CY

4 Vol. 25, No. 4 (Apr. 1988) TECHNICAL REPORT (Y, Koizumi et al.) 397 'jl :: 3 ;:;::.>< "" c; :: 3: ;:;:: BOO 6-2 " -- RELAP (a) Time 5 Broken loop hot leg -- RELAP Time 5 (b) Fig, 3(a),(b) Broken loop cold leg Comparison of broken loop hot and cold legs mass flows, meas. ured and calculated with original RELAP5/MOD2/CY36.2 of heat transfer calculation. m. DISCUSSION OF FIRST CALCULATION It is reported in Ref. (5) that the RELAP4 /MOD6 code<'ol could not calculate the temporary rewetting in Experiment L2-3 and the FRAP-T5<"l code could do so. The FRAP-T5 code was used for the rod heatup calculation but the thermal hydraulic boundary conditions for it were taken from the RELAP4/MOD6 calculation results. The main difference between the fuel rod models used in the RELAP4 /MOD6 and FRAP-T5 codes was the fuel and gap conductance models. The fuel relocation model used in the FRAP-T5 code produced a smaller gap width than the calculation with the RELAP4/MOD6 code, and the smaller gap width resulted in lower initial stored energy. During the heatup period of the blowdown, the heatup rate calculated with the FRAP-T5 code was smaller than that calculated with the RELAP4/MOD6 because the stored energy calculated with the FRAP-T5 was lower than that calculated with the RELAP4/MOD6 code. Therefore, the cladding surface temperature calculated with the FRAP-T5 code for Experiment L2-3 was lower than that calculated with the RELAP4/MOD6 code. As a result, the FRAP-T5 code calculated the temporary rewetting. Sensitivity calculations were performed in the present study to check the effect of the gap width with halved and doubled gap widths, respectively. The RELAP5/MOD2 code calculations had no fundamental change. The calculations failed to calculate the temporary rewetting. It is also reported in Ref. (9) that the RELAP5/MOD1 code<' 2 l could calculate the temporary rewetting in Experiment L2-3. In this calculation, Biasi's critical heat flux (CHF) correlation<' 3 l was incorporated into the code. The use of Biasi's CHF correlation is equivalent to increasing the CHF, which results in an increase in the minimum film boiling temperature. This will be discussed in the next Chap. IV. The minimum film boiling temperature is defined as the temperature where the heat transfer mode turns from film boiling heat transfer to transition boiling heat transfer during the rewetting or quenching phase. A sensitivity calculation was performed in the present study to check the effect of the CHF (and the minimum film boiling temperature) on the rewetting. In the calculation the RELAP5/MOD2 code was still used and the CHF was doubled. However, the code could not calculate the temporary rewetting. In the RELAP5/MOD2 code, Biasi's CHF correlation is used to calculate the CHF. The maximum linear heat generation rate during steady state conditions in Experiments L2-3 and LP-2-6 was 39.4 and 49.2 kw /m, respectively. In Experiment LP-2-6, the rod surface temperature after the initiation of the temperature excursion was higher than in Experiment L2-3. The sensitivity calculation results suggest that an increase in the minimum film boiling temperature in the modification was -75-

5 398 TECHNICAL REPORT (Y. Koizumi et al.) ]. Nucl. Sci. Technol., not enough in the. Experiment LP-2-6 calculation and to increase the CHF was not a correct direction to solve this problem. The rod surface temperature was measured with thermocouples welded on the external surface of the rod in the LOFT experiments. It was once a concern whether the external surface thermocouples might perturb temperature reading by providing nucleation sites or fin cooling which could then result in atypical rewetting. This effect was investigated in the Power Burst Facility and it was confirmed that the external surface thermocouple reduces the temperature response of the cladding to the initial boiling transition up to as much as 185 K, however the existence of the external surface thermocouples was not the cause of the temporary rewetting<">. It is concluded that the RELAP5/MOD2 code failed to calculate the temporary rewetting because of its poor ability to calculate the minimum film boiling temperature. IV. DISCUSSION OF MINIMUM FILM BOILING TEMPERATURE A great deal of research has been conducted on the minimum film boiling temperature, experimentally and analytically. However, most of all research is limitted to low pressure conditions and investigations for elevated pressure conditions, such as 7 MPa where the temporary rewetting was observed in LOFT Experiment LP-2-6, are scarce. Groeneveld & Stewart< > conducted experiments for measurement of the minimum film boiling temperature of water by using a sophisticated test section composed of a hot patch and a thin wall tube. The experiments covered pressures.1rv9 MPa, qualities -.12 rv.12 and flow rates 5rv2,7 kg/m 2 S. They proposed a correlation for the minimum film boiling temperature which is correlated with quality and the pressure for the subcooled condition and pressure for the saturated condition. Sakurai et al. 5 ' proposed correlations for the minimum film boiling temperature based upon their pool boiling experimental data below pressures of 2 MPa. In the experiments, they used 2 and 3 mm diameter rods and developed a correlation for each rod. Recently, the Japan Atomic Energy Research Institute conducted experiments for measurement of the minimum film boiling temperature for water< 1 by using a 5x5 multi-rod bundle made of Inconel 6 of the Two-Phase Flow Test Facility (TPTF)<m. The experimental conditions covered pressures 3rv 12 MPa and flow rates of water saturated at the inlet of the test section 3rv1,2 kg/m 2 s. Minimum film boiling temperature measured in the experiments are presented in Fig. 4 with values calculated with Groeneveld-Stewart's correlation and Sakurai's correlation for the rod of 3 mm diameter. In the figure, are also shown minimum film boiling temperature calculated with Berenson's correlation< 1 '' derived semi-analytically based upon the hydrodynamic instability theory and Berlin's correlation 9 ' derived empirically for cryogenic liquids, maximum water superheat temperatures calculated with Lienhard's correlation< 2 ' and saturation temperatures of water, for comparison. lqoq,...,"-t ;-== ,.,.,...,--,.---; TPTF DATA ; _.. / Groeneveld-Siewort.. / Sakurai 1151 /... e... enson 1111 I - - Berlin 1111 BOO / - lienoorcl'". --; L/ l---- Soluroflon L e /.{'.::.. IP- l 6 f! r -< v !/- 5 1 Pressure MPa Fig. 4 Minimum film boiling temperature me3.sured in TPTFO > The figure indicates that the measured minimum film boiling temperatures are nearly constant in the wide range of pressures investigated. The data are much higher than the maximum liquid superheat temperatures and considerably lower than values calculated with Berenson's correlation. The data compare well with values calculated with Groeneveld Stewart's correlation although the calculated

6 Vol. 25, No. 4 (Apr. 1988) TECHNICAL REPORT (Y. Koizumi et al.) 399 values are not smooth for pressure change and a little lower at 12 MPa. The values calculated with Sakurai's correlation compare well with data at 3 MPa, however considerably higher than data at 7 and 12 MPa which are far outside their experimental pressures. The values calculated with Berlin's correlation agree well with data at 3, 7 and 12 MPa, however they show quite different tendency from values with other correlations at low pressures ; decrease with increase in pressure. In conclusion, Groeneveld-Stewart's correlation provides the best fit curve for TPTF minimum film boiling temperature data even though there is minor peculiar tendency for pressure variation. That correlation may be reliable to predict the minimum film boiling temperature for a wide range of pressure since it is based upon experimental data.1 9MPa. One thing should be noted is lloeje et al.'s results<" 1 J of the measurement of the minimum film boiling temperature. They measured the minimum film boiling temperature of 96 1,17 K for water at a pressure of 6.9 MPa in the range of mass fluxes 6814kg/m 2 s and qualities.31. using a test piece with an inner diameter of 12.5 mm. Their data are considerably higher than the data in the TPTF experiments and Groeneveld-Stewart's data. They pointed out that axial conduction, surface roughness and increased wettability due to oxide film were primarily responsible for the elevated minimum film boiling temperatures. The same problem probably exists in the TPTF, Groeneveld-Stewart and also LOFT experiments. However, there is no firm basis to discuss it at present. V. MODIFICATION OF RELAP5 /MOD2 CODE ON MINIMUM FILM BOILING TEMPERA TURE AND TRANSITION BOILING HEAT TRANSFER RATE DURING REWETTING AND QUENCHING In the RELAP5/MOD2 code, the minimum film boiling temperature is not defined explicitly. It is defined as the intersection of the film boiling heat transfer rate line and the transition boiling heat transfer rate line on the heat flux vs. wall superheat surface as shown in Fig. 5(a). It was decided to use Groeneveld-Stewart's correlation to give the minimum film boiling temperature as discussed in Chap. N. (a) Transition Boiling Nucleate Bailin Wall Superheat, log LO.Ts I Original boiling curve (b) Fig. 5(a), (b) Transition Boiling I Film Boiling TMFB- Ts Wall Superheat, log IAT 5 1 TMFB 'Groeneveld-Steworl's Minimum Film Boiling Temperature Modified boiling curve for rewetting and quenching Boiling curve in RELAP5 /MOD2/CY36.2 Osakabe<""J presented the boiling curve during quenching process of heater rods as shown in Fig. 6. The results suggest that the heat flux during transition boiling increases to a high value at first, then it is nearly constant and close to the critical heat flux value of Kutateladze's CHF correlation< 23 J and finally moves to nucleate boiling heat flux. Inoue & Tanaka< J reported the same results as Osakabe's. Their results indicated that the heat flux during the transition boiling is slightly higher than the CHF with Kutateladze's correlation in low quality or subcooled conditions. Taking these facts into consideration, the simplified boiling curve shown in Fig. 5(b) is proposed. Since the period of transition boiling is very short, as shown in Fig. 6, the -77-

7 4 TECHNICAL REPORT (Y. Koizumi et al.) ]. Nucl. Sci. Techno/., 1 7 NE 1' : H G: " :X: Wall Superheol Fig. 6 Boiling curve during quenching process measured by Osakabe< 22 > simplification of the transition boiling curve has little effect on the results. This simplified boiling curve with Groeneveld-Stewart's minimum film boiling temperature correlation was incorporated into the RELAP5/MOD2 code. In the modification, the original CHF correlation of the RELAP5/MOD2 code is still used. The modified boiling curve is only used for the rewetting or quenching process in the code. VI. CALCULATED RESULTS WITH MODIFIED RELAP5/MOD2 CODE Peak power rod surface temperatures calculated with the RELAP5/MOD2 code modified as discussed in the Chap. V are compared with measured ones in Fig. 7(a)"-'(f). The modified RELAP5/MOD2 code shows some improvement in calculating the temporary rewetting in the early phase of blowdown. The first temperature excursion is well predicted in Fig. 7(a), however it occurs a little earlier in Fig. 7(b)"-'(d), and is not predicted in Fig. 7(e), (f) which are for the upper part of the core. Since the flow rate and void fraction changes calculated with the RELAP5 /MOD2 code during this period are quite similar among these core volumes, other factors might cause the miscalculation of the temperature excursion in the upper part of the core. It is considered that the heat flux in the upper part of the core did not exceed the CHF calculated with the code since the linear heat generation rate in the upper part of the core is much lower than that in the other parts of the core. Since nuclear fuel K rods were used in the LOFT experiments, it is hard to get exact heat flux distribution in the core. Thus, the code input data uncertainty for the heat flux might be the reason why the temperature excursion was not predicted in the upper part of the core although skepticism about the CHF calculation can't be rejected. As for the temporary rewetting in the early phase of blowdown, the modified RELAP5 code shows good improvement in predicting it in the lower part of the core, however the improvement is not sufficient in the middle of the core. In Fig. 7(a), (b), it is predicted to occur at almost the same timing as in the experiment. In Fig. 7(c), the code fails to predict it. In Fig. 7(d), the predicted temporary rewetting is later than in the experiment and the second temperature excursion starts before the cladding temperature returns to the saturation temperature. In Fig. 7(d), cladding temperature decreases slowly until the temporary rewetting in the calculation and the same tendency is observed in Fig. 7(c). In the experiment, the cladding temperatures drop sharply. The heat transfer mode during this period is film boiling heat transfer. It is supposed that the difference between the calculated and measured results may be caused by the effect of thermocouples mounted on the outer surface of the cladding in the experiment or poor estimation of the film boiling heat transfer in the calculation. In Fig. 7(a), (b) the sharp drop before the rewetting is calculated as in the experiment. Thus, the suspicion to the effect of the thermocouples mounted on the outer surface of the cladding is to be cleared. If the sharp drop of the cladding temperature during the film boiling period were calculated in Fig. 7(c), (d) as in Fig. 7(a), (b), the temporary rewetting could be calculated. Thus, it suggests that the film boiling heat transfer correlation used in the code needs to be refined. After temporary rewetting, the second temperature excursion starts at the lower and middle parts of the core, Fig. 7(a), (b) and (d). In Fig. 7(e), the temperature ceases to decrease and remains at the nearly constant value. The -78-

8 Vol. 25, No. 4 (Apr. 1988) TECHNICAL REPORT (Y. Koizumi et al.) 41 1 BOO - RELAP 5 ==)Dolo E <D! 1!. 8. l RELAP 5 =!Dolo \ 2 6 BO \ Time s Time s (a) (b) \ \ - RELAP 5 - RELAP5 e E Dolo Range <D )Data BOO -., 8.. :; 5! " Q ji \ BO \ Time Time s (c) (d) RELAP5 - RELAP5 e e Dolo <X> :::::::Joo1o <X> "" 8 8 /\ I I u (A is " u i { l./: - 8. : l e f (\ - e I Time s Time s (e) Fig. 7 (a)-(f) Comparison of cladding temperatures measured and calculated with modified RELAP5/MOD2/CY36.2 (f) distinct heatup is not again calculated at the upper part of the core. The void fraction during this period is large, rather close to one. The input data uncertainty and/or the CHF calculation may be the reason why the distinct heat up was not calculated at the upper part of the core again. The calculated rod surface temperatures are within the range of data during the second temperature excursion and quenching period in Fig. 7(a), (b) and (d). After the second temperature excursion, the data are oscillatory and different from rod to rod, even at positions of the same elevation. The calculated results are also oscillatory. It should be noted that the quencing phenomena is excellently calculated without the reflooding option of the code. In Fig. 7(c), since the cladding does not experience the temporary rewetting, the temperature remains at the higher value than in the experiment, and then begins to decrease -79-

9 42 TECHNICAL REPORT (Y. Koizumi et a/.) ]. Nucl. Sci. Technol., slowly to quite a low value. This result may suggest that Groeneveld-Stewart's minimum film boiling temperature correlation gives a little lower value late in the transient, i.e. at low pressure. For confirmation, the rod surface temperature calculated for Experiment L2-5 with the modified RELAP5/MOD2 code is presented in Fig. 8. In Experiment L2-5, the entire corewide temporary rewetting in the early phase of blowdown was not observed because of quick flow coast-down in the primary coolant system. The modified code also did not show the temporary rewetting and the result is consistent with the experimental results. >< u :> E! t >- T1me Fig. 8 Comparison of cladding temperatures, measured in Experiment L2-5 and calculated with modified RELAP5/MOD2/CY36.2 Although the RELAP5/MOD2 code modified with Groeneveld-Stewart's correlation provided good results, further investigation is necessary to give the entire credit to the RELAP5/MOD2 boiling curve with Groeneveld-Stewart's correlation. As for the CHF calculation, the timing of the first temperature excursion initiation calculated with the modified RELAP5/MOD2 code is generally a little earlier than the data. The core flow coast-down was well calculated as shown in Figs. 2 and 3. Thus, the CHF correlation or the initial stored energy in the fuel rods as pointed out in Ref. (5), might be a cause for the premature excursion. Further investigation is necessary. Film boiling heat transfer calculation also needs to be investigated as already mentioned. E!!! VH. CONCLUSION It is proposed that the minimum film boiling temperature be included explicitly in the RELAP5/MOD2 code and the transition boiling heat flux be increased. The modification from which this proposal was obtained was implemented by introducing Groeneveld-Stewart's minimum film boiling temperature correlation into the code and simplifying the transition boiling curve. The modified RELAP5/MOD2 code well predicted the rod surface temperature transient during the PWR cold-leg doubleended break LOCA experiment in the LOFT test facility, Experiment LP-2-6, including the temporary rewetting in the early phase of blowdown. This had not been calculated by RELAP5/MOD2 and other codes. ACKOWLEDGEMENT The authors wish to express their sincere thanks to Mr. R. R. Rohrdanz of EG & G Idaho, Inc. for reviewing the manuscript. ---REFERENCEE--- (1) REEDER, D. L. : LOFT system and test description (5.5 ft nuclear core LOCES), NUREG!CR- 247, TREE-128, (1978). (2) CoPLEN, H. L., YBARRONDO, L. J.: Loss-of-fluid test integral test facility and program, Nucl. Safety, 15, (1974). (3) BALL, L.]., et at.: Semiscale program description, TREE-NUREG-121, (1978). (4) ADACHI, H., et at.: ROSA- n experimental program for PWR LOCA/ECCS integral tests, ]AERI-1277, (1982). (5) NALEZNY, C. L.: Summary of Nuclear Regulatory Commission's LOFT program experiments, NUREG!CR-3214, EGG-2248, (1983). (6) ALoNso, A., et at.: Validation of TRAC-PD2 against Experiment LP-2-6 of the LOFT-OECD experiment, Trans. 14th Water Reactor Safety Information Mtg., NUREG!CP-81, (1986). (7) RANSOM, V. H., et at.: RELAP5/MOD2 code manual, NUREG/CR-4312, (1985). (8) GROENEVELD, D. C., STEWART, J. C.: The minimum film boiling temperature for water during film boiling collapse, Proc. 7th Int. Heat Transfer Conf., Miinchen, Vol. 4, FB37, (1982). (9) DEMMIE, P. N., et al.: Best estimate prediction for LOFT nuclear experiment L2-5, EGG-LOFT. 5869, (1982). -8-

10 Vol. 25, No. 4 (Apr. 1988) TECHNICAL REPORT (Y. Koizumi et a/.) 43 M EG & G Idaho Inc. : RELAP4/MOD6 a computer program for transient thermal-hydraulic analysis of nuclear reactors and related system user's manual, CDAP-TR-3, (1978). (11) SIEFKEN, L. J. : FRAP-T5; a computer code for the transient analyses of oxide fuel rods, NUREG!CR-84, TREE-1281, (1979). M RANSOM, V. H., et a/.: RELAP5/MOD1 code manual, NUREG/CR-1826, (1982). M BIASI, L., et a/.: Studies on burnout-part 3, Energ. Nucl., 14, (1967). M GARNER, R. W., MacDoNALD, P. E.: Power burst facility thermocouple effects test results report, Test series TC-1, TC-3 and TC-4, NUREG!CR- 2665, EGG-219, (198). M SAKURAI, A., et a/.: Effect of system pressure on film boiling heat transfer, minimum heat flux and minimum temperature, "Thermal Hydraulics of Nuclear Reactors", V. 1, ANS, 279 (1983). M ANODA, Y., et al.: Minimum film boiling temperature in high pressure quenching process for simulated fuel rod bundle, Preprint 1987 Fall Mtg. of At. Energy Soc. jpn., B25, (1987). (m NAKAMURA, H., et al.: System description for ROSA-IV Two-Phase Flow Test Facility (TPTF), ]AERI-M 83-42, (1983). M BERENSON, P. ]. : Film boiling heat transfer from a horizontal surface, Trans. ASME,! Heat Transfer, 83, (1961). (1 BERLIN, I. I., et al. : Study of critical film boiling under natural convection, lnzh. Fiz. Zh., 24[2], (1973). <) LIENHARD, ]. H.: Correlation for the limiting liquid superheat, Chem. Eng. Sci., 31 [9], (1976). I) ILOEJE,. C., et a/. : An investigation of the collapse and surface rewet in film boiling in forced vertical flow, Trans. ASME, ]. Heat Transfer, 97, (1975). OsAKABE, M. : Heat transfer of simulated fuel rods during reflood phase, Ph. D. Thesis, Univ. of Tokyo, 35 (1985). KuTATELADZE, S. S.: Zh. Thekh. Fiz., 2, (195). INOUE, M., TAN AKA, H. : A study on surface rewet caused by uniform collapse of flow film boiling, 65 Fall Annu. Mtg. of jpn. Soc. Mech. Eng., 911A, (1987). $ KUTATELADZE, S. S. : "Heat Transfer in Condensation and Boiling", (2nd ed.), Mashgiz, Moscow, AEC Trans!. 377, U.S. AEC Tech. Info. Service, (1952). $ NISHIKAWA, K., YAMAGATA, K.: On the correlation of nucleate boiling heat transfer, Int. f. Heat Mass Transfer, 1, (196). -81-