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Thermo-hydraulics for LMFBR's components
Nuclear E n g m e e n n g and Design 124 (1990) 379-389 North-Holland
379
Thermo-hydraulics for LMFBR's components J.L. Carbonnier
CEA /IRDI/DEDR /DRP, CEN/Cadarache, France F. Forestier
NOVA TOME, Lyon, France D. Grand
CEA /IRDI/DEDR /DTE, CEN/Grenoble, France C. Lacro~x
EDF/DER /LNH, Chatou, France P. P 6 t u r a u d
EDF/DER /TTA, Chatou, France
Experimental and theorltlCal studies have been performed for several years for hehcal steam generators, s o d i u m - s o d i u m exchangers and p~pmg stratification. For hehcal steam generators, two sodium heated mock-ups, wath 1:1 scaled exchange tube, and accurate thermal instrumentation in the tube walls, were budt: Catalina at Cadarache and H616na at les Renard16res. Results and interpretation gave reformation on dry-out m e c h a m s m s and thermal loading. For s o d m m - s o d l u m exchangers, mock-ups have been budt at Grenoble and Chatou to investigate the primary flow. A s o d m m - s o d i u m 4 M W exchanger mock-up is operated at Cadarache for thermo-hydrauhcs of edge channels, plugged tubes and strong buoyancy effects. For p~pmg stratlficaUon, experiments have been performed m water at Chatou, and m s o d m m at Grenoble. In the frame of studies for SPX2 a n d / o r EFR, new concepts have been studied once through straxght tube steam generators in modified 9% Cr ferrltlC steel. - "drum-type" s o d m m - a a r exchanger The speclfc tbermo-hydrauhcs of these components, and the R & D work undertaken m these f e l d s are described -
Des 6tudes th~,onques et exp6rlmentales sont effectu6es depuls plusleurs anu6es sur les g6ngrateurs de vapeur en hghce, sur les ~changeurs s o d m m - s o d l u m et sur les stratifications dans les tuyautenes. Pour les Ggngrateurs de Vapeur en h6hce, on a constrmt deux maquettes chauff6es au sodmm, avec des tubes h l'6chelle 1 et une instrumentation thermique dans l%'palsseur des tubes Catalina h Cadarache et Hglgna aux Renardl6res Les rgsultats et leur mterprgtaUon donnent des reformations sur les m6camsmes d'assSchement et les chargements therrmques Pour les 6changeurs s o d m m - s o d m m , des maquettes ont 6t6 constru~tes h Grenoble et Chatou pour &udler l'6coulement pnmatre. U n 6changeur maquette s o d i u m - s o d i u m de 4 M W est en essm/~ Cadarache pour 6tudler la thermohydrauhque des canaux de bords, l'mfluence de tubes bouchgs et la convection maxte Pour la straUficauon darts les tuyautenes, des expgnences ont 6t6 fmtes en eau h Chatou et en s o d m m h Grenoble Darts le cadre des 6tudes pour SPX2 e t / o u EFR, de nouveaux concepts ont 6t6 6tud16s des g6n6rateurs de vapeur h tubes drolts en acler 9% Cr modlfi6 des 6changeurs sodaum-aar de " t y p e tambour". On analyse les sp~clficltgs de ces composants sur le plan thermohydrauhque et on pr6sente la R & D correspondante -
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0029-54937907503.50
© 1990 - Elsevier Science Publishers
B.V. (North-Holland)
380
J L Carbonmer et al / Thermo-hydrauhcs for LMFBRs
1. I n t r o d u c t i o n
ator mock-ups, m order to study the behaviour of Super-Ph6mx steam generators (750 M W t h hehcal steam generator unit). One-dimensional calculation codes were developed at the same time Thermal fatigue cracks were found in tube welds on some mock-ups Therefore three other mock-ups were built. - The "3 Tubes" mock-up was budt and operated by the E D F to demonstrate, xn reahstlc operating conditions, the proper behavlour of Super-Ph6nlx units It reached this goal, but strong thermal fluctuations were observed in the sodium flow. - The two others: H616na ( E D F / L e s Renardl6res) and Catalina ( C E A / C a d a r a c h e ) were analyt,cal mockups They were under operation respectively unUl the end of 1987 and the rmddle of 1988. H616na's goal was to study specifically thermo-hydraullcs, whde the studies of Catahna included both thermo-hydrauhcs and mechanical behaviour by way of duration tests
The French program for thermo-hydraulics of Fast Breeder Reactor components may be dwlded into three parts. - hehcal steam generators - s o d i u m - s o d m m heat exchangers - others components: piping and new components for future projects (straight tube steam generators and verucal tube air coolers) We shall discuss these three parts (whxch differ from each other according to the relevant phenomena and their present status) in §§ 2, 3 and 4 of this paper In the conclusion (§ 5) we shall try to point out s~rmlanties in these programs and to relate them to the general trends of F B R components thermo-hydraullcs.
2. H e l i c a l s t e a m g e n e r a t o r s
[1] 2 1 Presentatton
A joint action, launched in 1986 between the CEA and the E D F , defined some c o m m o n tests on H~16na and Catahna to get more m f o r m a n o n from differences and complementant~es extsting between the two mock-
In the 1970s, an important experimental program had been performed on several hehcal tube steam gener-
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F~g. 1 H616na and Catahna mare charactenstlcs
J.L Carbonmer et al. / Thermo-hydrauhcsfor LMFBRs
381
way we tried to achieve the same conditions on the two mock-ups: hydraulic conditions on the w a t e r - s t e a m side - hydraulic conditmns on the s o d m m s~de heat flux calculated by the same one-dimensional code. Unfortunately, due to the loops charactenstms, some distorsions were unavoidable. The actual parameters of the c o m m o n tests are gtven m Table 1.
ups in order to better understand physical phenomena. The following subsections describe the two mock-ups, the test programs, the analysis method and the mare data acquired today. Some information is also given about other actions undertaken to improve the understanding of different behaviours noted between the 2 mock-ups and to explain thermal fluctuations observed on the sodium s~de.
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2.2. Descrtptton of the mock-ups These mock-ups are made of helical tubes in Alloy 800 of the same size as the Super-Ph6nix ones. The water-steam flows upwards inside the tubes and the sodium flows downwards in an annulus, nearly perpendicular to the tubes. One of the tubes on each mock-up is heavily instrumented with thermocouples, some of them are brazed inside the tube wall near the inner surface, others on, or just under the outer surface. The main differences between the mock-ups are: tube length and number (H616na: 5 tubes of 60 m, Catalina: 4 tubes of 85 m), hehx diameter, axaal pitch and instrumentation (see Fig. 1).
2.4. Types of analysts First, sodium temperature measurements are fitted with results of a one-dimensional code so that mean steam quality is known at the instrumented cross-sections. The statistical analysis includes the calculation of the mean values and the fluctuations. These are calculated from 1250 samples on 350 channels for H616na and from 2048 samples on 12 channels for Catahna. The dry-out mechamsm is denved from the analysis of three parameters on several azimuths on the tube: - The first parameter is the amplitude of thermal fluctuations near the inner surface of the tube: these thermal fluctuations reach a maxtmum at the dry out level. The second is the mean temperature near the inner surface: there is a sudden increase at the dry out level, corresponding to the transition between nucleate boihng and film boding regimes. - The third is the value of heat flux which sharply decreases at the dry out level; the steady state heat flux is calculated on the basts of mean values of measured temperatures in the tube wall. In order to make direct compansons between H616na and Catalina, we calculated (using the Radms code) the values of Catahna's temperatures at the location of
2.3. Test program Three categories of thermo-hydraulic tests have been performed to determine the temperature distnbutions m the tube wall and in the sodium flow: Steady state tests are the most numerous. They simulate operating conditions of Super-Ph6nix or they are c o m m o n tests. Some deal with the influence of water pressure or sodium velocity. Slow transients at startup and shutdown. Suspected hysteresis effects have been sought on H~16na. - Dynamic mstabihty tests. In this paper we shall focus on c o m m o n tests which have been operated with three loading levels. In this
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Table 1 Cohmon test's parameters Mass velocity water side (kg/m2s)
Low load Middle load High load
Pressure (bar)
Reynolds number on Na side
Number of working tubes
H61.
Cat.
H~I.
Cat.
H61
Cat.
H61
Cat.
568 1137 2273
568 1137 2273
173 174 178
172 171 174
5400 6100 6300
5300 6100 19800
5/5 2/5 1/5
2/4 2/4 2/4
J L Carbonmer et al / Thermo-hydrauhcs for LMFBRs
382
Hdldna's thermocouples. The R a d m s code is a linear transient thermal conducuon code used to reconstitute the complete temperature maps of the tube cross sections from the data filesfor the 12 synchronously strobed tube wall thcrrnocouplcs of Catahna mock-up [2]. A spectral analysis was also performed for long periods of temperature s~gnal (10-100 nun). W e checked that the s~gnal remained staUonary at both it's average value and varlancc. Spectral power, lustogram and correlations were computed 2 5 Ftrst conclustons, other acnons m progress
Typical results from statistical and spectral analys~s are presented m Figs. 2 and 3 (see also [3]). They show that temperature fluctuanons in the tube wall come from superimpositions of two separate phenomena: The dry-out phenomenon ms,de the tube. - A periodical phenomenon, outside the tube, related to the sodium flow.
2 5 1 The dry-out phenomenon
Consequences of dry-out are ~mportant only at low load. The energy of fluctuaUons ~s mcluded m a broad scale up to 2 Hz w~thout any characterisuc frequency, it decreases from the ms,de to the outside of tube. On the basis of the 3 parameters above, the dry-out scenario appears very clearly at low load and ~s different m Catahna and m Hdldna In Hdldna, the convenuonal stranficaUon due to mechanical effects (grawty and centrifugal forces) ~s observed- the dry-out occurs first on the upper azimuth (steam quality around 0 4) and ends on the lower one (steam quahty around 1) But m Catahna an lnversed straUfication IS observed with first dry-out on the lower azimuth (steam quahty < 0.6) and the last dry out on the upper azimuth (steam quahty around 1). The low value of heat flux on the upper azimuth (which ~s wet) may be explained by cold sodmm m the hydrauhc drag of the former tube (see § 2.5.4 ).
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A t the p r e s e n t time, there is n o clear e x p l a n a t i o n for t h e s e differences, b u t s o m e actions, in p r o g r e s s at the C E A a n d the E D F , are e x p e c t e d to p r o v i d e s o m e answers.
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Fig 3. Typmal results of spectral analysis (spectral power) at low load.
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J 1-, Carbonmer et al / Thermo-hydrauhcs for L M F B R s
first results are expected to be gamed by the beginning of 1990.
Table 3 Temperature differences in the sodium flow A, B, C, D defined on Fig. 4
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T B - TA
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Due to the exastence of a first and a last dry out, there is a strong overheating of steam by way of heat flux across the dried part of the cross section This leads to a thermodynarmc mls-balance in the double phase, and explains the very tugh values (even greater than one) of last dry out quality, calculated from measurements on mock-ups: the calculated thermodynamic quahty is greater than mass~c quality. Use of new correlations [4], including first and last dry-out qualities, in the one-dimensional code, allows for a more accurate prediction of wall temperatures in the post dry-out zone m accordance with experimental values. 2 5 3 P e n o d w a l p h e n o m e n o n on the s o d t u m stde
Temperature fluctuations in sodium appear with a very well defined characteristic frequency. These fluctuations are transrmtted to the tube wall with energy decreasing from the outside to the inside. The characteristlc frequency (around 1 Hz) is visible in the tube wall (particularly on the inner and outer azimuths) except when the dry-out fluctuations are too great at low load. This phenomenon from the sodium side preponderates over the dry-out fluctuations at middle load but chiefly at high load. The characteristic frequency seemed to be related to Strouhal number, so the E D F carried out actions [5] to ~mprove the understanding of hydraulics and thermodydrauhcs of sodium flow perpendicular to a row of tubes. These actions associate a refined numerical modelling with the Ulysse code (flmte differences, turbulence models mixing length and K - c ) and very detailed
Table 2 Computed and measured STROUHAL numbers
Ulyse code calculations Vulcam Water Mock-up HrMna and Catahna
Hrlrna axial pitch
Catahna axial pitch
0.37
0 33
0.36
0 33 to 0 36
0.37 to 0.40
0.23 to 0 28
20% 100%
experiments in water, air and sodium (Vulcam, Ath6na and H6pha3stos mock-ups). The first step of the hydrauhc phase, aamed at modelhng periodical flows, showed a good agreement between calculations, Vulcmn mock-up and the results measured o~ H616na and Catalina (see Table 2). It appears that only the mixing length model is able to represent this periodical behavlour; the unexpected inablhty of the standard K - c model might be found m its basic assumptions, lsotropy and spectrum equlhbrium of the turbulence Through the thermo-hydraulical phase (sodium tests on H6phaistos mock-up and new developments on thermal turbulence), the E D F intends to calculate thermal fluctuations. 2 5 4. Calculattons wtth the Trto code
The heat transfer is dependent from both the sodium side and w a t e r - s t e a m side. The effect of the sodium cross-flow has been assessed separately by means of the C E A T n o - V F code Due to symmetnes taken into account and to the turbulence model K - c used, the calculations are limited to the representation of a steady flow (no periodic fluctuations). The constant temperature of water and umform global heat exchange coefficient are considered Calculations with &fferent sodium velocities,
Table 4 Claudma mock-up characteristics Tube number: 60 (12 rows of 5) Tube &ameters 12-14mm Tube length. 4m Rectangular pitch 21 × 22mm Inlet/oulet windows height 0 3 m Variable inner edge gap: 17 9-27 3 mm Grids number. 4 Maximum thermal power 4 MW Instrumentation: 300 tbermocouples
J.L Carbonmeret al. / Thermo-hydrauhcsfor LMFBRs
385
3. Sodium-sodium heat exchangers
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characterised by the Reynolds number, and with different axial pitches, like the different mock-ups, permitted us to evaluate the influence of these parameters on the sodium temperature distribution. Results of these calculations are presented in Table 3 and an example of sodium flow for Catalina is shown in Fig. 4. It appears that, according to a large axial pitch (H616na), the upper half of the tube is uniformly heated. But, for a smaller pitch (as with Catalina), the upper surface of the tube is less heated than the inner and outer ones (therefore the heat flux is weak though the inner surface is wet). It can be supposed that, under a uniform heat flux, dry-out m the tube is mainly governed by mechanical forces, but when the upper surface heat flux is lower, the dry-out mechanism may be different. This is only a slight explanation and has to be confirmed with more sophisticated calculations. The influence of a plugged tube must also be taken into account. The sodium temperature spatial differences are greater as the axaal pitch and the sodium velocity become smaller.
The intermediate heat exchangers are made of straight tubes and are very sensitive to radial thermal differences. Such asymmetries were the main reason for the leakages observed on the Ph6nlx intermediate heat exchangers in 1976. In order to solve these problems, an important theorical and experimental program has been carried out by the CEA and the EDF. For bundles, the following parameters have to be correctly taken into account: - T r a n s v e r s e and obhque flows in inlet and outlet windows. - Hydraulic and geometric dlscontmuitxes: round or sharp margin, antivibratmg devices, deflectors or edge-gap along tuner or outer shells. - 2D and 3D codes have been developed m the CEA (Bacara, Trio) and m the EDF (M61odie), which solve Navier-Stokes and energy equations in a porous medium. The Fennec m water mock-up operated by the EDF in Chatou was one of the main validations of these programs for the hydraulics [6,7]. The Clara mock-up operated by the CEA m Grenoble with hot and cold water brings a vahdaUon of these codes for application to the decay heat removal sodmm-sodium coolers worlong in natural convection [8]. Today, the available codes m the CEA and the EDF allow a good prediction of thermo-dydraulic phenomena, nevertheless some uncertainties stdl remain. R & D actions are in progress to remove them. 3.2. Problems related to ctrcular pltch and mlet / outlet of bundle In France, the circular pattern has been chosen for the heat exchanger bundle. This pattern allows for a satisfactory knowledge of the edge gap effects with cylindrical shells, but such bundles have alternately aligned and staggered arrangements of tubes. These arrangements may have (according to Reynolds number and Pich/Diameter ratio) different head loss coefficients. The Clarisse m water mock-up models a 60 o sector of a circular pattern tube bundle. There are accurate velocity and pressure measurements in the aligned and staggered areas (see Fig. 5). The main characteristics are: circumferential pitch 20 mm, tube diameter 10 mm,
386
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This experiment also allows for measurements on head loss of the first rows of the bundle whose behavlour is known to be different from the average.
Usual modelling for mixed or natural convection uses the same correlations as forced convection (head loss and thermal exchange coefficients, temperature and velocity averaged by sub-channel). Thas modelling adds buoyancy terms, of course averaged by each sub-channel It proves to be correct if the local phenomenon of mixed convection does not appear (theoretically, they appear only at very low velocities). Such local imxed convection distorts velocity and temperature profiles near the tube's surface, and usual correlations do not remain valid The GR16 mock-up, operated m the CEA center of Grenoble, aims at an exploration of different regimes of mixed convection and especially at estabhshlng criteria for the emergence of local effects It is a sodium mock-up with electrical rods, and its mmn charactenstlcs are described in Fig. 6. Mobile devices allow very accurate measurements of the spatial variation of temperatures and velocities. First results were gained in 1989, and are presently under analysis.
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J.L. Carbonmer et al / Thermo-hydrauhcs for LMFBRs
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3.4. Thermal behavtour of bundles Figure 7 represents two types of discretlsation of tube bundles. In the first one (A), the more common, each row of tubes (with secondary fluid in it) exchanges heat with a single channel of primary fluid. Molecular and turbulent diffusmns are taken into account between two channels of primary fluid. In the second one (B), each row of tubes exchanges heat with two adjacent primary channels and each primary channel exchanges heat with two adjacent rows of tubes. Given the radial asymmetry of temperature, other things being equal, the B discretisation showed more important diffusion due to the coupling effect through the secondary fluid than the A one. This problem may occur in bundles with strong edge gap effects or plugged tubes. The Mortimer-Claudina program is expected to answer this kind of problem. It consists of two mock-ups with identical geometries. Mortimer is a water mock-up operated by the EDF at Chatou and provides accurate velocity measurements at the inlet and inside the bundle especially near the variable inner edge-gap. Claudina is a sodium mock-up operated by the CEA on the SET loop at Cadarache. The main characteristics of these mock-ups are listed in Table 4. In addition to the thermal effects of edge-gap at full power, the Claudina mock-up has been designed to study buoyancy effects at low load, valved off condiUons and the thermal effects of a plugged tube. The Mortimer and Claudina tests are presently in progress
4. O t h e r c o m p o n e n t s
4.1. Pipes The mam thermo-hydraulic problem for pipes is stratification.
387
Several experiments were performed in water by the EDF which showed the maan influence of parameters such as Richardson Number and the slope of temperature versus time at the inlet. These experiments also showed the influence of geometrical boundaries such as ascending or descending elbows, and the influence of mixing effects In elbows. Sodium experiments [9], performed by the CEA in Grenoble, confirmed the results acquired in water and showed the influence of the thermal inertia of the tube wall. They also showed that the stratified flow duration may be longer than the lmtial transient. Codes have been developed and qualified on the basis of these experiments [10,11,12]. They solve Navaer-Stokes and energy equations, with a K-c model for turbulence and 2 or 3D curvihnear meshes. The present status is a good understanding of stratification phenomena and availability of quahfied codes with Dven boundary conditions. One problem for apphcatlon to DHR loops working in natural convection is that stratification strongly modifies the global behavlour of the loop. So the operating codes, generally one-dimensional, are not able to predict correct boundary condiuons if they do not take into account the stratification. Hence, the next step in this field is couphng stratification codes to operating codes in order to correctly predict the behaviour of such loops during transients
4 2 Straight tube steam generators The Novatome company has worked for several years on the design of a straight tube steam generator made of 9% Cr 1 Mo VNb ferntic steel. This design is now the reference one for the European Fast Reactor project (EFR) As far as thermo-hydraulics is concerned, the main characteristics of this unit are: - A large unit size up to 600 MWt which leads to a large tube bundle diameter up to 1.5 m. - Use of entirely straight tubes without any flexlbihty device. - Once through concept with a single tube from subcooled water to superheated steam. Such characteristics need a very good knowledge of radial temperature differences during steady states, transients and working with plugged tubes. So, development and qualification of thermo-hydraulic multidimensional codes have to reach a very high level of accuracy and rehabllity.
388
J L Carbonmer et a l / Thermo-hydrauhcs for LMFBRs
This problem is more difficult to solve than the problem of sodium-sodium exchangers for two main reasons: - The water-steam double phase flow is more complex than the simple phase sodium flow. - When, in a sodmm-sodium exchanger, a local mcrease of primary sodium flow occurs, an increase of secondary flow (due to buoyancy effets) partially balances thermal effects. In a steam generator, a local increase of primary flow involves a decrease of water flow (due to higher head loss of the steam phase) which enhances thermal effects. Therefore, the water-steam side acts hke an amphfier of thermal asymmetries from the sodium side, and this aspect is sharper with once through umts. So, an important theoretical work on steam generator codes is underway in France, in collaboration with groups working on PWR steam generators (CEA codes Bacara-GV and Trio, EDF code: Cafca-Sicle). For a qualification of such codes, a sodium heated mock-up is now being designed for installation on the SET loop at Cadarache (where the Catalina mock-up was tested). This mock-up consists of one monotubular mock-up and one multltubular mock-up (seven tubes) installed in parallel. The tube diameter is full scale and its length is about 25 m. The monotubular mock-up may be instrumented with thermocouples inside the wall thickness and is devoted to checlang dry-out, heat exchange and head loss correlations. The multitubular mock-up will allow the study of dynarmc instabilities and thermo-hydrauhc behawour in asymmetrical thermal conditions (including plugged tube).
4 3 "'Drum-type" sodmm-atr coolers
Such sodium-air coolers studied by Novatome (first for SPX2 and now for EFR) are made of 3 or 4 rows of vertical finned tubes welded on 2 annular headers (Fig. 8). This conception makes important units up to 30 MWt possible and workang in natural convection on the sodium side feasible. The head loss on sodium side is very low. So, the following head losses which usually are considered neghg~ble have a notable influence on the thermo-hydraulics of this component: head loss at the inlet and outlet of each finned tube. This pressure loss is strongly influenced by the velocities of sodium in the annular headers. The hydraulic behavlour of headers due to single nozzle of sodium pipe.
s0dtum mlet II
l
l
sodium 1/ outlet i, Fig. 8. Scheme of "drum type" sodmm-alr cooler.
Buoyancy effects in the tubes, and in the lower header. During steady state working, these effects are involved at the result of the colder temperature of the inner row of tubes. The three above items have to be taken simultaneously into account for a thermo-hydraulic study of the lower header The Ana~l code, which models every tube, has been developed in the CEA; Anal1 models the header as one-dimensional pipes. In order to check 2 or 3D aspects, general purpose thermo-hydraulic codes (Trio) have been used. Work is still in progress to get codes fully adapted to the problems of this component. Of course, the experimental program is performed at the same time: - An analytical mock-up in order to check exchange and pressure loss coefficients with obhque air flow (EDF Chatou). - A hydraulic (360 °) mock-up to study the global behaviour on the air side (EDF Chatou). A water mock-up to study hydrauhcs of headers (CEA Grenoble). -A sodium mock-up on the SET loop at CEA Cadarache: 3 rows of 19 finned tubes to study thermo-hydrauhc behavaour ( operated in 1989). -
5.
C o n c l u s i o n
We have dealt with a number of components which differ from each other according to the status of their R & D programs. Thus, the paper lacks homogeneity. Nevertheless, a very strong trend does appear: the use
J L. Carbonnwr et al. / Thermo-hydrauhcs for LMFBRs
of more detailed models to obtain a better understandm g of the physical phenomena and more accurate predictions of temperature and velocity fields. This detailed modelling has been obtained by two means: - Increasing capabihties of globally specific 2D or 3D codes which model bundles as porous media. - The use of general thermo-hydraulic codes developed for cavities, to approach the local behaviour. The design and intrumentation of a large variety of mock-ups take into account these two aspects. This R & D work is used not only to improve the safety and rehability of components but also to improve and simplify their design. In this respect, a typical example is the design of a steam-generator with entirely straight tubes. This advanced design allows simplification in construction and cost reductaon but needs the complete understanding of thermo-hydrauhcs.
Acknowledgment The authors wish to thank MM.F. Baque, Y. Blanchet, G.M. Cicero, J. Dumesnil, B. Menant, Y. Severi and D. Tenchine who participated in writing this paper.
References [1] G.M. Cicero and Ph. Martin, "Thermohydrauhque de l'6coulement dans un tube euroul6 en h6lice: les programmes exp6rimentaux Catalina et H616na", Rev. Frangatse de Mdcamque 3, 133 (1985). [2] Ph. Martin, J.C. Dumas and J.Ph. Girard, "Thermomechanical stresses in the dryout zone of slightly reclined helically coded heat exchange tubes", BNRD Conference, Harrogate, October 1985.
389
[3] G.M. Cicero and P. Beaupied, "The H616na test program, description and analysis of the steady state operation", L I M E T Conf., Awgnon 17-21 October 1988. paper No. 119. [4] G. Berthoud, S. Jayanti, "Charactensatlon of dry out in hehcal coils", Int. J. Heat Mass Transfer (to be published). [5] V Czop, R. Lahrech and M. Robert, "Thermal hydraulic behaxaour of the local turbulent sodium cross-flow m a tube bundle applied to a LMFBR behcally coded tube steam generator", The Third Int Syrup. of Refined Flow Modelhng and Turbulence, Tokyo, July 1988. [6] F. Baron and E. Lana, "On the modelling of steady flows reside tube bundles of variable porosity", Proc. Third Int. Conf. on Reactor Thermo-hydrauhcs, Newport, October 1985. [7] D. Grand, B. Menant, P. Mercier and M. Vdland, "Numerical moddlmg of thermal hydraulics in heat exchangers", Natwnal Heat Transfer Conf., Pittsburg, 9-12 August 1987. [8] D. Grand, B. Menant and M. Vdland, "Natural convecuon m an immersion heat exchanger. Numerical simulauon apphed to water experiment and to LMFBR'S situataons", A I R H Second Int. Speclahst Meeting on Thermohydrauhcs tn LMFBR Rod Bundle, Roma 15-17 September 1982. [9] D. Tenchine, R. Martm, "Thermal strauflcadon in a horizontal sodium pipe", Int. Seminar of ICHMT, Dubrovnik, September 1980. [10] J.A. Toly and J. Legoft, "Thermal straUficatton in pipes: Najet sodium tests and Reycur calculations", A S M E Annual Meeting, New Orleans, 1984. [11] P.L. Viollet, J.P. Benque and J. Goussebafle, "Two chmenslonnal numerical modelling of non isothermal flows for unsteady thermal hydrauhc analysis", Nucl. Sc~. and Engrg 84, 350-372(1983). [12] M. Gabdlard and P.L. Viollet, "The three dmaensionnal computation of secondary flow and densRy currents in a curved pipe", 3rd Int. Syrup. Refined Flow ModeUmg and Turbulence Measurements, Tokyo, July 1988.
379
Thermo-hydraulics for LMFBR's components J.L. Carbonnier
CEA /IRDI/DEDR /DRP, CEN/Cadarache, France F. Forestier
NOVA TOME, Lyon, France D. Grand
CEA /IRDI/DEDR /DTE, CEN/Grenoble, France C. Lacro~x
EDF/DER /LNH, Chatou, France P. P 6 t u r a u d
EDF/DER /TTA, Chatou, France
Experimental and theorltlCal studies have been performed for several years for hehcal steam generators, s o d i u m - s o d i u m exchangers and p~pmg stratification. For hehcal steam generators, two sodium heated mock-ups, wath 1:1 scaled exchange tube, and accurate thermal instrumentation in the tube walls, were budt: Catalina at Cadarache and H616na at les Renard16res. Results and interpretation gave reformation on dry-out m e c h a m s m s and thermal loading. For s o d m m - s o d l u m exchangers, mock-ups have been budt at Grenoble and Chatou to investigate the primary flow. A s o d m m - s o d i u m 4 M W exchanger mock-up is operated at Cadarache for thermo-hydrauhcs of edge channels, plugged tubes and strong buoyancy effects. For p~pmg stratlficaUon, experiments have been performed m water at Chatou, and m s o d m m at Grenoble. In the frame of studies for SPX2 a n d / o r EFR, new concepts have been studied once through straxght tube steam generators in modified 9% Cr ferrltlC steel. - "drum-type" s o d m m - a a r exchanger The speclfc tbermo-hydrauhcs of these components, and the R & D work undertaken m these f e l d s are described -
Des 6tudes th~,onques et exp6rlmentales sont effectu6es depuls plusleurs anu6es sur les g6ngrateurs de vapeur en hghce, sur les ~changeurs s o d m m - s o d l u m et sur les stratifications dans les tuyautenes. Pour les Ggngrateurs de Vapeur en h6hce, on a constrmt deux maquettes chauff6es au sodmm, avec des tubes h l'6chelle 1 et une instrumentation thermique dans l%'palsseur des tubes Catalina h Cadarache et Hglgna aux Renardl6res Les rgsultats et leur mterprgtaUon donnent des reformations sur les m6camsmes d'assSchement et les chargements therrmques Pour les 6changeurs s o d m m - s o d m m , des maquettes ont 6t6 constru~tes h Grenoble et Chatou pour &udler l'6coulement pnmatre. U n 6changeur maquette s o d i u m - s o d i u m de 4 M W est en essm/~ Cadarache pour 6tudler la thermohydrauhque des canaux de bords, l'mfluence de tubes bouchgs et la convection maxte Pour la straUficauon darts les tuyautenes, des expgnences ont 6t6 fmtes en eau h Chatou et en s o d m m h Grenoble Darts le cadre des 6tudes pour SPX2 e t / o u EFR, de nouveaux concepts ont 6t6 6tud16s des g6n6rateurs de vapeur h tubes drolts en acler 9% Cr modlfi6 des 6changeurs sodaum-aar de " t y p e tambour". On analyse les sp~clficltgs de ces composants sur le plan thermohydrauhque et on pr6sente la R & D correspondante -
-
0029-54937907503.50
© 1990 - Elsevier Science Publishers
B.V. (North-Holland)
380
J L Carbonmer et al / Thermo-hydrauhcs for LMFBRs
1. I n t r o d u c t i o n
ator mock-ups, m order to study the behaviour of Super-Ph6mx steam generators (750 M W t h hehcal steam generator unit). One-dimensional calculation codes were developed at the same time Thermal fatigue cracks were found in tube welds on some mock-ups Therefore three other mock-ups were built. - The "3 Tubes" mock-up was budt and operated by the E D F to demonstrate, xn reahstlc operating conditions, the proper behavlour of Super-Ph6nlx units It reached this goal, but strong thermal fluctuations were observed in the sodium flow. - The two others: H616na ( E D F / L e s Renardl6res) and Catalina ( C E A / C a d a r a c h e ) were analyt,cal mockups They were under operation respectively unUl the end of 1987 and the rmddle of 1988. H616na's goal was to study specifically thermo-hydraullcs, whde the studies of Catahna included both thermo-hydrauhcs and mechanical behaviour by way of duration tests
The French program for thermo-hydraulics of Fast Breeder Reactor components may be dwlded into three parts. - hehcal steam generators - s o d i u m - s o d m m heat exchangers - others components: piping and new components for future projects (straight tube steam generators and verucal tube air coolers) We shall discuss these three parts (whxch differ from each other according to the relevant phenomena and their present status) in §§ 2, 3 and 4 of this paper In the conclusion (§ 5) we shall try to point out s~rmlanties in these programs and to relate them to the general trends of F B R components thermo-hydraullcs.
2. H e l i c a l s t e a m g e n e r a t o r s
[1] 2 1 Presentatton
A joint action, launched in 1986 between the CEA and the E D F , defined some c o m m o n tests on H~16na and Catahna to get more m f o r m a n o n from differences and complementant~es extsting between the two mock-
In the 1970s, an important experimental program had been performed on several hehcal tube steam gener-
630
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4 Thermal measurement points in s e v e r a l c r o s s s e c t i o n s .
l r l £I CFOSS s e c t l o D .
F~g. 1 H616na and Catahna mare charactenstlcs
J.L Carbonmer et al. / Thermo-hydrauhcsfor LMFBRs
381
way we tried to achieve the same conditions on the two mock-ups: hydraulic conditions on the w a t e r - s t e a m side - hydraulic conditmns on the s o d m m s~de heat flux calculated by the same one-dimensional code. Unfortunately, due to the loops charactenstms, some distorsions were unavoidable. The actual parameters of the c o m m o n tests are gtven m Table 1.
ups in order to better understand physical phenomena. The following subsections describe the two mock-ups, the test programs, the analysis method and the mare data acquired today. Some information is also given about other actions undertaken to improve the understanding of different behaviours noted between the 2 mock-ups and to explain thermal fluctuations observed on the sodium s~de.
-
-
2.2. Descrtptton of the mock-ups These mock-ups are made of helical tubes in Alloy 800 of the same size as the Super-Ph6nix ones. The water-steam flows upwards inside the tubes and the sodium flows downwards in an annulus, nearly perpendicular to the tubes. One of the tubes on each mock-up is heavily instrumented with thermocouples, some of them are brazed inside the tube wall near the inner surface, others on, or just under the outer surface. The main differences between the mock-ups are: tube length and number (H616na: 5 tubes of 60 m, Catalina: 4 tubes of 85 m), hehx diameter, axaal pitch and instrumentation (see Fig. 1).
2.4. Types of analysts First, sodium temperature measurements are fitted with results of a one-dimensional code so that mean steam quality is known at the instrumented cross-sections. The statistical analysis includes the calculation of the mean values and the fluctuations. These are calculated from 1250 samples on 350 channels for H616na and from 2048 samples on 12 channels for Catahna. The dry-out mechamsm is denved from the analysis of three parameters on several azimuths on the tube: - The first parameter is the amplitude of thermal fluctuations near the inner surface of the tube: these thermal fluctuations reach a maxtmum at the dry out level. The second is the mean temperature near the inner surface: there is a sudden increase at the dry out level, corresponding to the transition between nucleate boihng and film boding regimes. - The third is the value of heat flux which sharply decreases at the dry out level; the steady state heat flux is calculated on the basts of mean values of measured temperatures in the tube wall. In order to make direct compansons between H616na and Catalina, we calculated (using the Radms code) the values of Catahna's temperatures at the location of
2.3. Test program Three categories of thermo-hydraulic tests have been performed to determine the temperature distnbutions m the tube wall and in the sodium flow: Steady state tests are the most numerous. They simulate operating conditions of Super-Ph6nix or they are c o m m o n tests. Some deal with the influence of water pressure or sodium velocity. Slow transients at startup and shutdown. Suspected hysteresis effects have been sought on H~16na. - Dynamic mstabihty tests. In this paper we shall focus on c o m m o n tests which have been operated with three loading levels. In this
-
-
-
Table 1 Cohmon test's parameters Mass velocity water side (kg/m2s)
Low load Middle load High load
Pressure (bar)
Reynolds number on Na side
Number of working tubes
H61.
Cat.
H~I.
Cat.
H61
Cat.
H61
Cat.
568 1137 2273
568 1137 2273
173 174 178
172 171 174
5400 6100 6300
5300 6100 19800
5/5 2/5 1/5
2/4 2/4 2/4
J L Carbonmer et al / Thermo-hydrauhcs for LMFBRs
382
Hdldna's thermocouples. The R a d m s code is a linear transient thermal conducuon code used to reconstitute the complete temperature maps of the tube cross sections from the data filesfor the 12 synchronously strobed tube wall thcrrnocouplcs of Catahna mock-up [2]. A spectral analysis was also performed for long periods of temperature s~gnal (10-100 nun). W e checked that the s~gnal remained staUonary at both it's average value and varlancc. Spectral power, lustogram and correlations were computed 2 5 Ftrst conclustons, other acnons m progress
Typical results from statistical and spectral analys~s are presented m Figs. 2 and 3 (see also [3]). They show that temperature fluctuanons in the tube wall come from superimpositions of two separate phenomena: The dry-out phenomenon ms,de the tube. - A periodical phenomenon, outside the tube, related to the sodium flow.
2 5 1 The dry-out phenomenon
Consequences of dry-out are ~mportant only at low load. The energy of fluctuaUons ~s mcluded m a broad scale up to 2 Hz w~thout any characterisuc frequency, it decreases from the ms,de to the outside of tube. On the basis of the 3 parameters above, the dry-out scenario appears very clearly at low load and ~s different m Catahna and m Hdldna In Hdldna, the convenuonal stranficaUon due to mechanical effects (grawty and centrifugal forces) ~s observed- the dry-out occurs first on the upper azimuth (steam quality around 0 4) and ends on the lower one (steam quahty around 1) But m Catahna an lnversed straUfication IS observed with first dry-out on the lower azimuth (steam quahty < 0.6) and the last dry out on the upper azimuth (steam quahty around 1). The low value of heat flux on the upper azimuth (which ~s wet) may be explained by cold sodmm m the hydrauhc drag of the former tube (see § 2.5.4 ).
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/ Thermo-hydrauhcsfor
A t the p r e s e n t time, there is n o clear e x p l a n a t i o n for t h e s e differences, b u t s o m e actions, in p r o g r e s s at the C E A a n d the E D F , are e x p e c t e d to p r o v i d e s o m e answers.
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LMFBRs
383
T h e D a h l i a e x p e r i m e n t in p r o g r e s s at the E D F a i m s at the d e t e r m i n a t i o n of s t r u c t u r e of d i p h a s i c flow In an h e h c a l tube; it u s e s w a t e r - s u l f u r h e x a f l u o r l d e a n d m e a s u r e m e n t s o f void r a t i o a n d t h i c k n e s s of liquid film. the
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Fig 3. Typmal results of spectral analysis (spectral power) at low load.
384
J 1-, Carbonmer et al / Thermo-hydrauhcs for L M F B R s
first results are expected to be gamed by the beginning of 1990.
Table 3 Temperature differences in the sodium flow A, B, C, D defined on Fig. 4
2 5 20verheatmg
Axial pitch (mm)
Corresponding mock-up
Reynolds Number
T B - TA
T D - T¢
56
Catahne
96
Hrl~na
4400 18000 5400
13 5 58 40
8.6 43 07
o f s t e a m tn double p h a s e area
Due to the exastence of a first and a last dry out, there is a strong overheating of steam by way of heat flux across the dried part of the cross section This leads to a thermodynarmc mls-balance in the double phase, and explains the very tugh values (even greater than one) of last dry out quality, calculated from measurements on mock-ups: the calculated thermodynamic quahty is greater than mass~c quality. Use of new correlations [4], including first and last dry-out qualities, in the one-dimensional code, allows for a more accurate prediction of wall temperatures in the post dry-out zone m accordance with experimental values. 2 5 3 P e n o d w a l p h e n o m e n o n on the s o d t u m stde
Temperature fluctuations in sodium appear with a very well defined characteristic frequency. These fluctuations are transrmtted to the tube wall with energy decreasing from the outside to the inside. The characteristlc frequency (around 1 Hz) is visible in the tube wall (particularly on the inner and outer azimuths) except when the dry-out fluctuations are too great at low load. This phenomenon from the sodium side preponderates over the dry-out fluctuations at middle load but chiefly at high load. The characteristic frequency seemed to be related to Strouhal number, so the E D F carried out actions [5] to ~mprove the understanding of hydraulics and thermodydrauhcs of sodium flow perpendicular to a row of tubes. These actions associate a refined numerical modelling with the Ulysse code (flmte differences, turbulence models mixing length and K - c ) and very detailed
Table 2 Computed and measured STROUHAL numbers
Ulyse code calculations Vulcam Water Mock-up HrMna and Catahna
Hrlrna axial pitch
Catahna axial pitch
0.37
0 33
0.36
0 33 to 0 36
0.37 to 0.40
0.23 to 0 28
20% 100%
experiments in water, air and sodium (Vulcam, Ath6na and H6pha3stos mock-ups). The first step of the hydrauhc phase, aamed at modelhng periodical flows, showed a good agreement between calculations, Vulcmn mock-up and the results measured o~ H616na and Catalina (see Table 2). It appears that only the mixing length model is able to represent this periodical behavlour; the unexpected inablhty of the standard K - c model might be found m its basic assumptions, lsotropy and spectrum equlhbrium of the turbulence Through the thermo-hydraulical phase (sodium tests on H6phaistos mock-up and new developments on thermal turbulence), the E D F intends to calculate thermal fluctuations. 2 5 4. Calculattons wtth the Trto code
The heat transfer is dependent from both the sodium side and w a t e r - s t e a m side. The effect of the sodium cross-flow has been assessed separately by means of the C E A T n o - V F code Due to symmetnes taken into account and to the turbulence model K - c used, the calculations are limited to the representation of a steady flow (no periodic fluctuations). The constant temperature of water and umform global heat exchange coefficient are considered Calculations with &fferent sodium velocities,
Table 4 Claudma mock-up characteristics Tube number: 60 (12 rows of 5) Tube &ameters 12-14mm Tube length. 4m Rectangular pitch 21 × 22mm Inlet/oulet windows height 0 3 m Variable inner edge gap: 17 9-27 3 mm Grids number. 4 Maximum thermal power 4 MW Instrumentation: 300 tbermocouples
J.L Carbonmeret al. / Thermo-hydrauhcsfor LMFBRs
385
3. Sodium-sodium heat exchangers
,tII: ,iiI
3.1. Presentatton
t t A
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characterised by the Reynolds number, and with different axial pitches, like the different mock-ups, permitted us to evaluate the influence of these parameters on the sodium temperature distribution. Results of these calculations are presented in Table 3 and an example of sodium flow for Catalina is shown in Fig. 4. It appears that, according to a large axial pitch (H616na), the upper half of the tube is uniformly heated. But, for a smaller pitch (as with Catalina), the upper surface of the tube is less heated than the inner and outer ones (therefore the heat flux is weak though the inner surface is wet). It can be supposed that, under a uniform heat flux, dry-out m the tube is mainly governed by mechanical forces, but when the upper surface heat flux is lower, the dry-out mechanism may be different. This is only a slight explanation and has to be confirmed with more sophisticated calculations. The influence of a plugged tube must also be taken into account. The sodium temperature spatial differences are greater as the axaal pitch and the sodium velocity become smaller.
The intermediate heat exchangers are made of straight tubes and are very sensitive to radial thermal differences. Such asymmetries were the main reason for the leakages observed on the Ph6nlx intermediate heat exchangers in 1976. In order to solve these problems, an important theorical and experimental program has been carried out by the CEA and the EDF. For bundles, the following parameters have to be correctly taken into account: - T r a n s v e r s e and obhque flows in inlet and outlet windows. - Hydraulic and geometric dlscontmuitxes: round or sharp margin, antivibratmg devices, deflectors or edge-gap along tuner or outer shells. - 2D and 3D codes have been developed m the CEA (Bacara, Trio) and m the EDF (M61odie), which solve Navier-Stokes and energy equations in a porous medium. The Fennec m water mock-up operated by the EDF in Chatou was one of the main validations of these programs for the hydraulics [6,7]. The Clara mock-up operated by the CEA m Grenoble with hot and cold water brings a vahdaUon of these codes for application to the decay heat removal sodmm-sodium coolers worlong in natural convection [8]. Today, the available codes m the CEA and the EDF allow a good prediction of thermo-dydraulic phenomena, nevertheless some uncertainties stdl remain. R & D actions are in progress to remove them. 3.2. Problems related to ctrcular pltch and mlet / outlet of bundle In France, the circular pattern has been chosen for the heat exchanger bundle. This pattern allows for a satisfactory knowledge of the edge gap effects with cylindrical shells, but such bundles have alternately aligned and staggered arrangements of tubes. These arrangements may have (according to Reynolds number and Pich/Diameter ratio) different head loss coefficients. The Clarisse m water mock-up models a 60 o sector of a circular pattern tube bundle. There are accurate velocity and pressure measurements in the aligned and staggered areas (see Fig. 5). The main characteristics are: circumferential pitch 20 mm, tube diameter 10 mm,
386
J L Carbonmer et al / Thermo-hydrauhcs for LMFBRs
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This experiment also allows for measurements on head loss of the first rows of the bundle whose behavlour is known to be different from the average.
Usual modelling for mixed or natural convection uses the same correlations as forced convection (head loss and thermal exchange coefficients, temperature and velocity averaged by sub-channel). Thas modelling adds buoyancy terms, of course averaged by each sub-channel It proves to be correct if the local phenomenon of mixed convection does not appear (theoretically, they appear only at very low velocities). Such local imxed convection distorts velocity and temperature profiles near the tube's surface, and usual correlations do not remain valid The GR16 mock-up, operated m the CEA center of Grenoble, aims at an exploration of different regimes of mixed convection and especially at estabhshlng criteria for the emergence of local effects It is a sodium mock-up with electrical rods, and its mmn charactenstlcs are described in Fig. 6. Mobile devices allow very accurate measurements of the spatial variation of temperatures and velocities. First results were gained in 1989, and are presently under analysis.
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tube length 1.871 m and height of inlet window 541 mm. Results m Fig. 5 show an appreciable difference between aligned and staggered areas, and prediction with 2D code using average head loss coefficient values. The full interpretation of this experiment is in progress: Measurement and evaluation by 3D calculations of propagauon along the bundle of hydraulic asymmetries. -Evaluation by 3D calculation of thermal consequences and hence uncertainties involved m the 2D model.
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J.L. Carbonmer et al / Thermo-hydrauhcs for LMFBRs
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3.4. Thermal behavtour of bundles Figure 7 represents two types of discretlsation of tube bundles. In the first one (A), the more common, each row of tubes (with secondary fluid in it) exchanges heat with a single channel of primary fluid. Molecular and turbulent diffusmns are taken into account between two channels of primary fluid. In the second one (B), each row of tubes exchanges heat with two adjacent primary channels and each primary channel exchanges heat with two adjacent rows of tubes. Given the radial asymmetry of temperature, other things being equal, the B discretisation showed more important diffusion due to the coupling effect through the secondary fluid than the A one. This problem may occur in bundles with strong edge gap effects or plugged tubes. The Mortimer-Claudina program is expected to answer this kind of problem. It consists of two mock-ups with identical geometries. Mortimer is a water mock-up operated by the EDF at Chatou and provides accurate velocity measurements at the inlet and inside the bundle especially near the variable inner edge-gap. Claudina is a sodium mock-up operated by the CEA on the SET loop at Cadarache. The main characteristics of these mock-ups are listed in Table 4. In addition to the thermal effects of edge-gap at full power, the Claudina mock-up has been designed to study buoyancy effects at low load, valved off condiUons and the thermal effects of a plugged tube. The Mortimer and Claudina tests are presently in progress
4. O t h e r c o m p o n e n t s
4.1. Pipes The mam thermo-hydraulic problem for pipes is stratification.
387
Several experiments were performed in water by the EDF which showed the maan influence of parameters such as Richardson Number and the slope of temperature versus time at the inlet. These experiments also showed the influence of geometrical boundaries such as ascending or descending elbows, and the influence of mixing effects In elbows. Sodium experiments [9], performed by the CEA in Grenoble, confirmed the results acquired in water and showed the influence of the thermal inertia of the tube wall. They also showed that the stratified flow duration may be longer than the lmtial transient. Codes have been developed and qualified on the basis of these experiments [10,11,12]. They solve Navaer-Stokes and energy equations, with a K-c model for turbulence and 2 or 3D curvihnear meshes. The present status is a good understanding of stratification phenomena and availability of quahfied codes with Dven boundary conditions. One problem for apphcatlon to DHR loops working in natural convection is that stratification strongly modifies the global behavlour of the loop. So the operating codes, generally one-dimensional, are not able to predict correct boundary condiuons if they do not take into account the stratification. Hence, the next step in this field is couphng stratification codes to operating codes in order to correctly predict the behaviour of such loops during transients
4 2 Straight tube steam generators The Novatome company has worked for several years on the design of a straight tube steam generator made of 9% Cr 1 Mo VNb ferntic steel. This design is now the reference one for the European Fast Reactor project (EFR) As far as thermo-hydraulics is concerned, the main characteristics of this unit are: - A large unit size up to 600 MWt which leads to a large tube bundle diameter up to 1.5 m. - Use of entirely straight tubes without any flexlbihty device. - Once through concept with a single tube from subcooled water to superheated steam. Such characteristics need a very good knowledge of radial temperature differences during steady states, transients and working with plugged tubes. So, development and qualification of thermo-hydraulic multidimensional codes have to reach a very high level of accuracy and rehabllity.
388
J L Carbonmer et a l / Thermo-hydrauhcs for LMFBRs
This problem is more difficult to solve than the problem of sodium-sodium exchangers for two main reasons: - The water-steam double phase flow is more complex than the simple phase sodium flow. - When, in a sodmm-sodium exchanger, a local mcrease of primary sodium flow occurs, an increase of secondary flow (due to buoyancy effets) partially balances thermal effects. In a steam generator, a local increase of primary flow involves a decrease of water flow (due to higher head loss of the steam phase) which enhances thermal effects. Therefore, the water-steam side acts hke an amphfier of thermal asymmetries from the sodium side, and this aspect is sharper with once through umts. So, an important theoretical work on steam generator codes is underway in France, in collaboration with groups working on PWR steam generators (CEA codes Bacara-GV and Trio, EDF code: Cafca-Sicle). For a qualification of such codes, a sodium heated mock-up is now being designed for installation on the SET loop at Cadarache (where the Catalina mock-up was tested). This mock-up consists of one monotubular mock-up and one multltubular mock-up (seven tubes) installed in parallel. The tube diameter is full scale and its length is about 25 m. The monotubular mock-up may be instrumented with thermocouples inside the wall thickness and is devoted to checlang dry-out, heat exchange and head loss correlations. The multitubular mock-up will allow the study of dynarmc instabilities and thermo-hydrauhc behawour in asymmetrical thermal conditions (including plugged tube).
4 3 "'Drum-type" sodmm-atr coolers
Such sodium-air coolers studied by Novatome (first for SPX2 and now for EFR) are made of 3 or 4 rows of vertical finned tubes welded on 2 annular headers (Fig. 8). This conception makes important units up to 30 MWt possible and workang in natural convection on the sodium side feasible. The head loss on sodium side is very low. So, the following head losses which usually are considered neghg~ble have a notable influence on the thermo-hydraulics of this component: head loss at the inlet and outlet of each finned tube. This pressure loss is strongly influenced by the velocities of sodium in the annular headers. The hydraulic behavlour of headers due to single nozzle of sodium pipe.
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Buoyancy effects in the tubes, and in the lower header. During steady state working, these effects are involved at the result of the colder temperature of the inner row of tubes. The three above items have to be taken simultaneously into account for a thermo-hydraulic study of the lower header The Ana~l code, which models every tube, has been developed in the CEA; Anal1 models the header as one-dimensional pipes. In order to check 2 or 3D aspects, general purpose thermo-hydraulic codes (Trio) have been used. Work is still in progress to get codes fully adapted to the problems of this component. Of course, the experimental program is performed at the same time: - An analytical mock-up in order to check exchange and pressure loss coefficients with obhque air flow (EDF Chatou). - A hydraulic (360 °) mock-up to study the global behaviour on the air side (EDF Chatou). A water mock-up to study hydrauhcs of headers (CEA Grenoble). -A sodium mock-up on the SET loop at CEA Cadarache: 3 rows of 19 finned tubes to study thermo-hydrauhc behavaour ( operated in 1989). -
5.
C o n c l u s i o n
We have dealt with a number of components which differ from each other according to the status of their R & D programs. Thus, the paper lacks homogeneity. Nevertheless, a very strong trend does appear: the use
J L. Carbonnwr et al. / Thermo-hydrauhcs for LMFBRs
of more detailed models to obtain a better understandm g of the physical phenomena and more accurate predictions of temperature and velocity fields. This detailed modelling has been obtained by two means: - Increasing capabihties of globally specific 2D or 3D codes which model bundles as porous media. - The use of general thermo-hydraulic codes developed for cavities, to approach the local behaviour. The design and intrumentation of a large variety of mock-ups take into account these two aspects. This R & D work is used not only to improve the safety and rehability of components but also to improve and simplify their design. In this respect, a typical example is the design of a steam-generator with entirely straight tubes. This advanced design allows simplification in construction and cost reductaon but needs the complete understanding of thermo-hydrauhcs.
Acknowledgment The authors wish to thank MM.F. Baque, Y. Blanchet, G.M. Cicero, J. Dumesnil, B. Menant, Y. Severi and D. Tenchine who participated in writing this paper.
References [1] G.M. Cicero and Ph. Martin, "Thermohydrauhque de l'6coulement dans un tube euroul6 en h6lice: les programmes exp6rimentaux Catalina et H616na", Rev. Frangatse de Mdcamque 3, 133 (1985). [2] Ph. Martin, J.C. Dumas and J.Ph. Girard, "Thermomechanical stresses in the dryout zone of slightly reclined helically coded heat exchange tubes", BNRD Conference, Harrogate, October 1985.
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[3] G.M. Cicero and P. Beaupied, "The H616na test program, description and analysis of the steady state operation", L I M E T Conf., Awgnon 17-21 October 1988. paper No. 119. [4] G. Berthoud, S. Jayanti, "Charactensatlon of dry out in hehcal coils", Int. J. Heat Mass Transfer (to be published). [5] V Czop, R. Lahrech and M. Robert, "Thermal hydraulic behaxaour of the local turbulent sodium cross-flow m a tube bundle applied to a LMFBR behcally coded tube steam generator", The Third Int Syrup. of Refined Flow Modelhng and Turbulence, Tokyo, July 1988. [6] F. Baron and E. Lana, "On the modelling of steady flows reside tube bundles of variable porosity", Proc. Third Int. Conf. on Reactor Thermo-hydrauhcs, Newport, October 1985. [7] D. Grand, B. Menant, P. Mercier and M. Vdland, "Numerical moddlmg of thermal hydraulics in heat exchangers", Natwnal Heat Transfer Conf., Pittsburg, 9-12 August 1987. [8] D. Grand, B. Menant and M. Vdland, "Natural convecuon m an immersion heat exchanger. Numerical simulauon apphed to water experiment and to LMFBR'S situataons", A I R H Second Int. Speclahst Meeting on Thermohydrauhcs tn LMFBR Rod Bundle, Roma 15-17 September 1982. [9] D. Tenchine, R. Martm, "Thermal strauflcadon in a horizontal sodium pipe", Int. Seminar of ICHMT, Dubrovnik, September 1980. [10] J.A. Toly and J. Legoft, "Thermal straUficatton in pipes: Najet sodium tests and Reycur calculations", A S M E Annual Meeting, New Orleans, 1984. [11] P.L. Viollet, J.P. Benque and J. Goussebafle, "Two chmenslonnal numerical modelling of non isothermal flows for unsteady thermal hydrauhc analysis", Nucl. Sc~. and Engrg 84, 350-372(1983). [12] M. Gabdlard and P.L. Viollet, "The three dmaensionnal computation of secondary flow and densRy currents in a curved pipe", 3rd Int. Syrup. Refined Flow ModeUmg and Turbulence Measurements, Tokyo, July 1988.