LIVE-3D and LIVE-2D Experimental Results on Melt Pool Heat Transfer With Top Cooling Conditions

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1 6 th European Revew Meetng on Severe Accdent Research (ERMSAR-2013) Avgnon (France), Palas des Papes, 2-4 October, 2013 LIVE-3D and LIVE-2D Expermental Results on Melt Pool Heat Transfer Wth Top Coolng Condtons ABSTRACT X. GAUS-LIU, A. MIASSOEDOV T. CRON, B. FLUHRER Karlsruhe Insttute of Technology, Germany (KIT) LIVE programme nvestgates the late n-vessel debrs and melt pool behavour n severe accdents n lght water reactors. The LIVE test programme ncludes LIVE-3D and LIVE-2D facltes. The LIVE-3D test vessel s hemspherc and the LIVE-2D test vessel s semcrcular. Both test vessels have the same dameter. A seres of test wth coolng the melt pool from the top haven been performed both n LIVE-3D and LIVE-2D facltes. Smulant materals of 20 mol % NaNO 3-80 mol % KNO 3 and water have been used for the top coolng tests. Three top coolng tests were performed n LIVE 3D faclty. The test condtons dffered n smulant materals and external coolng condton. Each test had four power plateaus. Three top coolng tests were performed n LIVE-2D faclty wth dfferent power generaton rates. The ward and downward heat transfer behavour of the melt pool are compared between LIVE-3D tests and LIVE-2D tests. Although smlar heat flux dstrbuton along the vessel wall s observed for LIVE-3D and LIVE-2D tests, LIVE-2D test results have shown hgher heat transfer coeffcent to the top of the melt pool as compared to the LIVE-3D tests and results from the prevous studes. Water as smulant materal has shown lower heat transfer both to the per surface and to the curved vessel wall. The outcomes of the LIVE top-coolng tests provde a new nsght for the evaluaton of the establshed -Ra correlatons. 1 INTRODUCTION The n-vessel melt retenton (IVR) by floodng the reactor vessel wall externally s regarded as an effectve severe accdent management strategy [1]. The effectveness of ths method depends on whether local heat flux from the melt pool through the wall s lower than the crtcal heat flux (CHF) removable by the external coolng water. Top coolng by coolng the per surface of a molten pool n the lower head, f coolng water can be managed to be nduced to the the reactor pressurzed vessel, could be an addtonal mgtaton strategy to reduce thermal loads at the vessel wall. Certanly other responces such as steam and hygrogen producton, the possblty of pressure ncrease shoud be evaluated. On the other hand a two-layer melt pool can be formed at certan melt composton wth a metallcal layer atop of an oxde layer [2]. A hgh heat transfer coeffcent from the oxde layer wards to the metallc layer can tapferng the heat flux at the metallc layer, thus transfer the crtcal thermal load to the metallc layer. Tll now a numerous expermental and analytcal studes have been undertaken to chararaterze the ward and downward heat transfer behavour of the oxde melt pool. The expermental studes are dfferent n geometry (3D or 2D), smulant materals (water, molten salts or prototypcal corum), boundary coolng condtons (sothermal or not) and smulaton of the nternal heat sources (drect electrcal heatng, nductve heatng, mcrowave, transent coolng and so on) [3] [4] [5] [6] [7] [8]. The queston s how predctve are the results obtaned from dfferent expermental geometres, boundary condtons or smulant materals? The objectve of the study at KIT s to perform a seres of top-coolng tests n LIVE-3D and LIVE-2D facltes to nvestgate the comparablty of the results frstly from hermspherc and sem-crcle geometry and secondly from dfferent smulant melts. LIVE-3D and LIVE-2D test vessels have the same dameter of 1 m. In the tests the same smulant materal (a non-eutectc mxture of 20 mol % NaNO 3-80 mol % KNO 3 ), the same heatng method Sesson 2, paper 2.9 1/14 pages

2 6 th European Revew Meetng on Severe Accdent Research (ERMSAR-2013) Avgnon (France), Palas des Papes, 2-4 October, 2013 (electrcal resstance heatng cable) and the same coolng condton are used [9] [10] [11]. Besdes the characterzaton of heat flux dstrbuton, the /down heat flux splttng n the melt pool s the man nterest of the study. Nomenclature Arabc c p thermal capacty (J/g/ C) g gravtatonal acceleraton (m/s 2 ) H pool heght (m) ΔH tr enthalpy of phase transton (J/g) ΔH fus enthalpy of fuson (J/g) L characterstc length n and Ra (m) ql sselt number ( T max Tnt) q heat flux (W/m 2 ) 5 Ra nternal Raylegh number g. q L ( ) power source densty (kw/m³) q Pr Prandtl number (ν/α) T temperature ( C or K) Q rate of heat nput or heat transfer (W) volume of melt pool (m³) V pool Greek α thermal dffusvty (m 2 /s) C ) ( p β thermal expanson coeffcent (1/K) θ polar angle of the vessel wall lower head ( ) λ thermal conductvty (W/(mK)) ν knematc vscosty (m 2 /s) ρ densty (kg/m³) Subscrpt n mean nt lq max mean p tr w 2 EXPERIMENTS nput global mean value of the vessel wall downward heat transfer nterface lqudus maxmum mean value of the whole vessel wall below melt surface or the whole pool at the poston of the pool surface phase transton ward heat transfer heat transfer through the vessel wall 2.1 Test faclty descrpton The LIVE-3D test vessel smulates the hemsphercal lower plenum of reactor pressurzed vessel of a PWR n 1:5 scale [12] [13]. The melt surface can be ether free surface by coverng the test vessel wth an nsulaton ld [14] [15] or be cooled wth a water-coolng ld. The test vessel wth top coolng ld s shown n Fgure 1. The test vessel and the top coolng ld are made of stanless steel SS316T. The nner dameter of the test vessel s 1 m and the wall thckness s ~25 mm. The test vessel s enclosed n a coolng vessel to enable external coolng wth ether water or ar. The coolng water flows n from the bottom and Sesson 2, paper 2.9 2/14 pages

3 6 th European Revew Meetng on Severe Accdent Research (ERMSAR-2013) Avgnon (France), Palas des Papes, 2-4 October, 2013 flows out va a sde outlet at top of the coolng vessel. For the top coolng there are 4 perpheral water nlets and 1 central outlet at the coolng ld. The coolng ld s mounted at 41.3 cm of vessel heght. The radus of the coolng ld s 46 cm. There s a gap of about 3.6 cm between the coolng ld and the vessel wall. The water flow rate of both external coolng and top coolng can be regulated. The decay power of the melt s smulated by 8 planes of electrcal resstance heatng cols, whch can be controlled ndvdually to realze homogenous power generaton n the melt pool. The dstance between heatng planes and between the wndngs s about 45 mm. The maxmum possble homogenous heat generaton s 29 kw. The lqud smulant melt s prepared n an external heatng furnace. The lqud melt at a gven temperature can be then poured nto the test vessel ether centrally or near the vessel wall. Top-coolng ld Test vessel Coolng vessel Fgure 1. LIVE-3D test vessel wth the top coolng ld. The LIVE-3D test vessel s extensvely nstrumented. Melt pool temperatures are measured by 57 thermocoles dstrbuted n n the melt. 17 pars of thermocoles are located at the vessel nner and outer surface at polar angles of 0, 30, 51, 65 and 76.5 and at four azmuthal orentatons. The wall temperatures enable the determnaton of the heat flux dstrbuton. Crust formaton and growth s montored by 3 thermocole trees at polar angles 37.6, 52.9 and Two vdeo cameras are nstalled for the observaton of melt pourng process. The vessel s placed on three weghtng cells, so that the weght changes durng melt pourng and melt extracton can be controlled. Detaled descrpton of the nstrumentaton s gven n [9]. The LIVE-2D test vessel s a slce whch s also 1:5 scaled to the reactor pressure vessel. The nner dameter of the test vessel and the wall thckness are the same as the LIVE-3D vessel. The wdth of the slce vessel s ~12 cm. The front and the back walls of the slce are also made of stanless steel and are nsulated to reduce heat losses, as shown n Fgure 2. The test vessel can be cooled at the outsde and at the top. For the external coolng the water can flow from the water nlet at the bottom wards to the left and the rght sde. For the LIVE-2D top coolng a rectangular coolng ld s mounted at the heght of 46 cm. The water flows from the center to the left and the rght edges of the ld. For the smulaton of decay heat source heatng elements are used and they can be controlled ndvdually and allow a quas-homogeneous heat generaton rate of maxmum 13 kw [10]. Sesson 2, paper 2.9 3/14 pages

4 6 th European Revew Meetng on Severe Accdent Research (ERMSAR-2013) Avgnon (France), Palas des Papes, 2-4 October, 2013 Fgure 2. LIVE-2D test vessel wth (left) and wthout front and back walls (rght). The LIVE-2D test vessel s nstrumented wth a set of 13 thermocoles n the melt and 10 pars of thermocoles at dfferent locatons at the vessel wall nner and outer surface. Based on these temperatures, heat flux dstrbuton through the vessel wall s calculated. Crust formaton and growth s montored by thermocole trees ntrudng from the nner wall nto the melt at 6 dfferent locatons. LIVE-3D and LIVE-2D use the same heatng furnace for the melt generaton and dscharge. The smulant melt s heated to 350 C n the heatng furnace before t s poured nto a test vessel. One test phase at one heat generaton rate s termnated when the thermodynamc steady state of the melt pool s approached. At the end of each test, the resdual melt s extracted back to the heatng furnace va a vacuum pump. A non-eutectc bnary mxture of 20 mol% NaNO 3-80 mol% KNO 3 composton s selected as smulant materal of corum for the frst seres of LIVE tests. Accordng to own measurements [16], the soldus temperature of ths mxture s about 223 C and the lqudus temperature s about 284 C. Other physcal propertes of the smulant are gven n Table 1. Table 1. Thermal-physcal propertes of 20 mol% NaNO 3-80 mol% KNO 3. c p thermal capacty J/g/ C ρ densty kg/m³ T tr /T lq ΔH tr/ ΔH fus ν β λ Sesson 2, paper 2.9 Transton/lqudus temperature, Transton/fuson enthalpy, knematc vscosty, thermal expanson rate themal conductvty unt sold lqud C J/g T ( C) (119 C<T<182 C) [KIT measurement] [KIT measurement ] [KIT measurement] 65.7, 60 C-118 C [KIT measurement ] x10-6 m²/s E-4 T( C) (300 C<T<400 C) [KIT measurement ] at 284 C; at 340 C [17] [KIT measurement] at 220 C-286 C [KIT measurement ] 1.75 at 300 C; 1.35 at 350 C [17] x10-4 /K, 3.81 [17] W/(mK) [KIT test data] at 300 C at 350 C [17] 4/14 pages

5 2.2 Test programm 6 th European Revew Meetng on Severe Accdent Research (ERMSAR-2013) Avgnon (France), Palas des Papes, 2-4 October, 2013 Three top-coolng tests were carred out n the LIVE-3D faclty. The test condtons were dfferent regardng the smulaton materal and coolng condtons. As t s shown n Table 2, 20% NaNO 3-80% KNO 3 salt was used as the smulant materal n L7V and L7TC tests, whereas water was the smulant materal n L7W test. Durng L7V and L7W tests, both top coolng surface and external coolng at the vessel wall were performed whereas durng L7TC test only the top ld was water cooled, and there was no external water coolng at the vessel wall. The water flow nlet and outlet temperature dffered n ~10 C, so that the dfference s large enough for an accurate calculaton of heat removed from the top and from the sde of the vessel. Four power generaton rates n the same order were appled n all three tests. The melt pool heght n LIVE-3D tests was kept 1-2 cm above the lower plate of the coolng ld to nsure a good contact between the melt pool and the coolng ld. Also three top-coolng tests were performed n the LIVE-2D faclty. Both the melt surface and the vessel wall were water-cooled n all tests. Three levels of power nput were realzed of each test. The tests dffered only n the order of the power plateaus. The melt pool heght n LIVE-2D tests was 46 cm. Table 2. Test programm of top-coolng test n LIVE-3D and LIVE-2D facltes. LIVE-3D Coolng condtons Upper ld Vessel wall Power nput [kw] LIVE-2D Coolng condtons Upper ld Vessel Wall Power nput [kw] L7V (salt test) water water 29->24-> 18->9 L00A1 water water 7.3->6.3 ->4.2 L7W (water test) water water 29->24-> 18->9 L01 water water 7.3->3.7 ->7.3 L7TC (salt test) water No water coolng 29->24-> 18->9 L02 water water 3.7->7.3 ->3.7 3 RESULTS 3.1 Melt temperature and heat flux profles of LIVE-3D tests The melt temperature vertcal dstrbuton measured at the radus of 3 cm s shown n Fgure 3. For the tests wth external coolng, L7V and L7W, the melt pool has a lower zone wth temperature stratfcaton and a well-mxed per zone. However the proporton of the two zones and the temperature gradent at the lower zone are dfferent. If the melt temperatures are normalzed n terms of ΔT/ΔT mean, whereas T T T and ΔT T T nt mean mean nt the normalzed temperature dstrbuton s shown n Fgure 4. Comparng the salt test L7V wth a unform nterface temperature, T T, the water test L7W has a hgher nt temperature gradent n the lower zone and a larger well-mxed per zone. The per part of the pool n water test locates at H/H p >0.4 whereas n salt test at H/H p >0.7. The locaton of the per zone s compared wth results from other facltes. For water as lq Sesson 2, paper 2.9 5/14 pages

6 6 th European Revew Meetng on Severe Accdent Research (ERMSAR-2013) Avgnon (France), Palas des Papes, 2-4 October, 2013 smulant, n SIMECO test the lower boundary of the per zone s H/H p s 0.6 [6] and n BALI test the H/H p s about 0.5 [4]. Both the SIMECO and BALI tests were performed n slce geometry. In the water test L7W the temperature near the bottom of the pool was lower than the average nterface temperature T nt. In the salt test L7V the temperature at the pool bottom should be also lower than the nterface temperature due to the crust formaton. However, due to the lowest heatng plane n the LIVE-3D faclty the melt temperature shows hgher values. The melt temperature near the top surface s about 1.2 tmes of the global mean melt temperature for both the salt test and the water test. The dfferent temperature profles between the water test and the salt test can be caused by a number of reasons. The materal propertes n terms of the Prandtl number can be a major one. The Pr of the ntrate salt s n the range of 8-10; the Pr of water s between 2.8 and 4. Crust formaton can also exert nfluence that the nterface temperature between the melt and the crust was unform and equal to the lqudus temperature. However, ths assumpton cannot be fully certfed. In the BALI water experments, the coolng concept enabled ce formaton at the vessel wall, nevertheless the temperature profle was smlar to the profle observed n L7W test. In the test wthout external water coolng (L7TC test) the melt temperature s almost sothermal (Fgure 3 b)). The overall temperature was ~10 C hgher than the maxmum melt temperature of L7V, however t was ~27 C lower than the maxmum temperature of a melt temperature, C kW 24kW 18kW 9kW melt temperature, C kw 24 kw 18 kw 9 kw heght, mm (a) L7V heght, mm (b) L7TC melt temperature, C KW 24kW 18kw 9 kw heght, mm (c) L7W melt pool wth an nsulated top ld [15]. Sesson 2, paper 2.9 6/14 pages

7 6 th European Revew Meetng on Severe Accdent Research (ERMSAR-2013) Avgnon (France), Palas des Papes, 2-4 October, 2013 Fgure 3. Melt temperature dstrbuton of (a) L7V test, (b) L7TC test, (c) L7W test. 1,4 1,2 1,0 ΔT/ΔT mean 0,8 0,6 0,4 0,2 L7V 29 kw 0,0 L7W 29 kw -0,2 L7TC 29 kw -0,4-0,6 0,0 0,2 0,4 0,6 0,8 1,0 H/H p, - Fgure 4. Comparson of normalzed temperature dstrbuton. The horzontally averaged heat fluxes along the polar angle of the curved sdewall are shown n Fgure 5. The man source of the uncertanty s the system error of the thermocoles whch are mounted at the wall nner and outer surface. The system error s comparatvely large for low heat flux. The scatterng range of local heat fluxes at one horzontal level but dfferent azmuthal orentaton s about 8-16 %. Generally the heat flux n the salt test L7V s hgher than the water test L7W. In L7V the heat flux below polar angle below 30 C was stagnated or even decreased along polar angle, and was ncreased lnear above ths poston. For the water test the heat flux ncreased from the bottom tll polar angle 50 and kept constant above ths poston. q, W/m² kW 24 kw 18 KW 9kW q, W/m² kW 24 kw 18 KW 9kW polar angle, polar angle, Fgure 5. Heat flux profles along the vessel wall of L7V test (left) and L7W test (rght). The normalzed heat flux values weghted by the area-mean heat flux, q/q mean, are also gven n Fgure 5. The maxmum heat flux n the salt test s about 1.7 tmes and n water test s 1.3 tmes hgher than the mean value. The q / q max mean rato s compared to other Sesson 2, paper 2.9 7/14 pages

8 6 th European Revew Meetng on Severe Accdent Research (ERMSAR-2013) Avgnon (France), Palas des Papes, 2-4 October, 2013 studes. In salt test, SIMECO s value was 1.7 both for eutectc and non-eutectc salt [6]. In water tests there are larger dfference. In mn-acopo [7] and BALI tests q / q max mean s about 1.7 [4], whereas n SIMECO t s 1.3. In the study of Jahn&Renecke [5], the q / q max mean of expermental results s between for sem-crcular geometry. 2,0 2,0 q/q mean 1,5 1,0 29kW 24 kw 18 kw 9 kw q/q mean 1,5 1,0 29kW 24 kw 18 kw 9 kw 0,5 0,5 0,0 0,0 0,2 0,4 0,6 0,8 1,0 θ/θ p 0,0 0,0 0,2 0,4 0,6 0,8 1,0 θ/θ p Fgure 6. Normalzed heat flux profles of L7V (left) and L7W (rght). 3.2 Heat flux and melt temperature profles of LIVE-2D tests The am of LIVE-2D tests s to nvestgate the comparablty of the melt behavour between hemspherc and sem-crcular geometres. Concernng the top coolng condton, two salt tests wth smlar power source denstes are selected for the comparson: LIVE-3D L7V 18 kw and LIVE-2D 3.7 kw. The power denstes of the LIVE-3D L7V 18 kw and LIVE-2D 3.7 are 92 kw/m³ and 88 kw/m³ respectvely. The normalzed melt temperature and heat flux profles are shown n Fgure 7. Both the melt temperature dstrbuton and the heat flux of LIVE-2D test have the smlar profles as the LIVE-3D tests. In the per part of the melt pool the normalzed melt temperatures and heat fluxes n LIVE-2D tests were slghtly hgher than the results n LIVE-3D tests: ΔT max /ΔT mean s 1.2 and the q / q max mean s about 1.9. Based on the smlar q / q max mean a general concluson can be drawn that for sothermal coolng condton at the top and at the sdewall, and Pr of the melt s about 7, the maxmum heat flux s about tmes of the mean heat flux. Ths maxmum to mean value can be at least appled for Ra between Comparng a melt pool wthout top coolng, for example the LIVE-L10 test [15] whose q / q max mean s between 2.3 to 2.5, top coolng concept s very benefcal for an oxde pool. Snce top-coolng concept not only extracts a large part of the decay heat, but also reduce the taperng of the heat flux near the melt per surface. Despte of the smlarty of the dstrbuton characterstcs between sem-crcular and hemspherc geometres through the curved vessel wall, sgnfcant dfferences are observed concernng the heat transfer to the top surface and through the sdewall n real values, whch can be shown n the followng descrpton of the top/sde heat transfer rato and the sselt number. Sesson 2, paper 2.9 8/14 pages

9 6 th European Revew Meetng on Severe Accdent Research (ERMSAR-2013) Avgnon (France), Palas des Papes, 2-4 October, ,6 1,4 LIVE 3D L7V 18kW LIVE 2D 00A1 3.7kW 2,5 LIVE 3D L7V 18kW LIVE-2D 3.7kW 1,2 2,0 ΔT/ΔT mean 1,0 0,8 0,6 q/q mean 1,5 1,0 0,4 0,2 0,5 0,0 0,0 0,2 0,4 0,6 0,8 1,0 0,0 0,0 0,2 0,4 0,6 0,8 1,0 H/H p, - θ/θ p Fgure 7. LIVE 3D and LIVE 2D comparson of normalzed melt temperature (left) and heat flux (rght). 3.3 Energy balance, top/down heat transfer rato The energy balance between power nput and the heat extracted from the melt by the top coolng and external coolng s frstly examned. In Table 3 and Table 4 the heat transfer data of LIVE-3D tests and LIVE-2D tests are gven respectvely. A total heat transfer rato s defned as ( Q w Q ) / Q, where Q n w and Q represents the heat removed by the coolng water from the sdes of the vessel and by the top coolng ld respectvely. For LIVE-3D L7V and L7W tests the total heat transfer rate s about 0.85, for L7TC ths rate s lower snce there was no water coolng at the vessel wall and the heat transfer through the vessel s not consdered. For LIVE-2D test, the total heat transfer rato s about 1. The heat loss n LIVE-3D faclty could be the thermal radaton or heat convecton from the melt surface to the envronment at the gap between the top ld and the vessel wall. The melt surface area at the gap, whch counts about 12% of the total melt surface area, could play an mportant role of the heat loss. In LIVE-2D test, the gap between coolng ld and vessel wall s smaller than LIVE-3D and t was flled wth crust durng the whole test perod. q Table 3. LIVE-3D tests energy balance and top/down heat transfer ratos. kw/ m³ LIVE-3D LIVE-L7V LIVE-L7W LIVE-L7TC Q n kw (Q w +Q ) /Q n - Q / Q q / q Ra E Sesson 2, paper 2.9 9/14 pages

10 q 6 th European Revew Meetng on Severe Accdent Research (ERMSAR-2013) Avgnon (France), Palas des Papes, 2-4 October, 2013 Table 4. LIVE-2D tests energy balance and top/down heat transfer ratos. L00A1- P1 L00A1- P2 LIVE-2D L00A1- P3 L01-P1 L01-P2 L01-P3 L02-p1 L02-P2 L02-P3 kw/m³ Q n kw (Q W +Q ) /Q n Q / Q q / q Ra 1.2 E E E E The man nterest of the study, the top/sdeward heat flux splttng top/sdeward heat flux rato average value of 5.3 Q / Q and the q / q are compared between LIVE-3D and LIVE-2D tests. The Q / Q n L7V s 1.7 and n L7W s 1.2, however t s 3.4 n LIVE-2D tests. That means the heat splttng rato n LIVE-2D s twce as hgher as n LIVE-3D tests. The top/down heat flux rato n L7V s 3.7 n average whereas n LIVE-2D t s 5.1 n average. The LIVE-2D test results mply a much stronger ward heat transfer n 2D than n 3D geometry. 3.4 sselt numbers The wards and downwards sselt number s calculated accordng to Eq (1) ql ( T max Tnt Where q s the average heat flux through vessel wall or top-coolng ld. L s the heght of melt pool wthout consderng the crust thckness at the vessel bottom and the T max s the maxmum melt pool temperature. In the salt test L7V and all LIVE-2D tests T nt s the lqudus temperature of the actural melt. Thus T nt s unform for all melt boundares n salt tests. In water test L7W T nt s the average nner surface temperature for the sdewall and the average temperature at the downsde of the bottom plate for the coolng ld. The T nt for the coolng ld s hgher than T nt for the vessel wall n water test. For salt test the Prantl number s n the range of 8-11, and for water test Pr s between The nternal Raylegh number s calculated accordng to Eq (2): Ra n ) g. q L /( a ) The ward and downward sselt numbers n relaton wth the nternal Raylegh number are shown n Fgure 8. For comparson, the results of other studes whch have the smlar Raylegh number range, such as SIMECO [6], Mn-ACOPO [7], Asfa&Dhr [18], Maynger [19] and Stenberner&Renecke are also shown n Fgure 8. The Ra- correlatons and applyng Ra number range of the studes are gven n Table 5. Except SIMECO experments, other correlatons comes from experments usng water as smulant materal. 5 (1) (2) Sesson 2, paper /14 pages

11 6 th European Revew Meetng on Severe Accdent Research (ERMSAR-2013) Avgnon (France), Palas des Papes, 2-4 October, ,E+12 1, 1,E+14 1,E+15 1,E+16 1,E+17 nternal Ra, - L7V L7W L7 TC LIVE 2D SIMECO Mn- ACOPO Asfa Stenberner &Renecke BALI, ,E+12 1, 1,E+14 1,E+15 1,E+16 1,E+17 nternal Ra, - L7V L7W LIVE 2D SIMECO Mn-ACOPO Asfa&Dhr Maynger BALI Fgure 8. Comparson of ward nusselt number (left) and downward nusselt number (rght) among LIVE 3D, LIVE 2D and other studes. The ward sselt number of the LIVE salt test L7V s n the same order of magntude as n other studes. However, L7TC test and especally all LIVE-2D tests have shown hgher ward sselt number. The n LIVE-2D s about 30% hgher than the other correlatons. In the contrast, the of the water test L7W s lower than the other correlatons. Consderng the downward sselt number n the salt tests, an opposte trend s observed. L7TC and LIVE-2D salt tests have lower value than L7V and other studes. The rato of / was also evaluated and s shown n Fgure 9. For the salt tests / s dentcal to water test a certan devaton to q / q due to the unform nterface temperature T nt ; n the q / q could be observed. In the LIVE-3D tests the / rato s about 3, whereas n the LIVE-2D tests ths rato s between 4 and 5. In SIMECO and mn-acopo tests / s about 2. There s also a general statement n [20], that / s ~2 and the proporton of the decay power transferred to the top s about 50 %. In the study of Mayrnger [19], who nvestgated n a semcrcular geometry wth Ra of , a trend of ncreasng / wth Ra s obtaned. Accrodng to Maynger s calculaton, / could be ~3 at Ra of The benefcal effect of top coolng by relevng the thermal load of vessel wall at the oxde pool s already dscussed. However, a strong ward heat transfer also means that more heat wll be transferred to the metallc layer atop of the oxde layer f the melt pool has two layers. A hgh / rato n ths case can result n hgh heat flux at the vessel wall at the metallc layer, ncreasng the focusng effect. Sesson 2, paper /14 pages

12 6 th European Revew Meetng on Severe Accdent Research (ERMSAR-2013) Avgnon (France), Palas des Papes, 2-4 October, 2013 Table 5. Summary of the studes of the Ra- relatons concernng hemspherc (3D) and semcrcular (2D) geometres. Ref Ra Pr Geometr y Maynger [19] ACOPO 1.95Ra E16 7- [8] Ra Ra E7- E Ra Mn- ACOPO [7] Ra E E Ra, E12 Ra 3E Ra 0.27, 3E13 Ra 7E14 7 2D H=R 3D, R=2 m H=R 3D, R=0.4 m H=R Upper Surface Cooled (sothermal ) Cooled, transent coolng Cooled, transent coolng Smulant - Water Water, Freon-113 ULCA 1) Asfa&Dh r [18] 0.55Ra Ra ( H R) E11 -E14 8 3D R1=0.4 m R2=0.6 m H/R=0.5-1 Cooled rgd wall and nsulated rgd wall Water, ethanol, olve ol, Freon-113 BALI and COPOII- AP [4] R R,3D,2D v,2d v,3d 0.116( H R (4V (3V pool pool / L) / 2 ) v,2d v,3d ) 0.32 Ra , 8 BALI: 2D R=2 m COPO: 2D R=2 m Cooled and free surface BALI: Water Ra E E ( H R ) Ra COPOII- AP: H 2 O+ZnSO 4 1) s ±17% of the UCLA correlaton for both surface nsulaton and coolng stuatons, s taken from Kulack&Emara 6 5 / LIVE-3D L7V LIVE-3D L7W LIVE-2D SIMECO Asfa&Dhr mn-acopo 0 1,0E+12 1,0 nternal Ra 1,0E+14 1,0E+15 Sesson 2, paper /14 pages

13 6 th European Revew Meetng on Severe Accdent Research (ERMSAR-2013) Avgnon (France), Palas des Papes, 2-4 October, 2013 Fgure 9. / of LIVE-3D, LIVE 2D and other studes. 4 CONCLUSIONS Top coolng as an addtonal mtgaton method of IVR can effectvely reduce the maxmum melt temperature and the maxmum heat flux through the vessel wall of an oxde melt pool, f the possble negatve effects of top coolng, such as steam and hydrogen generaton can be managed. However top coolng also mples a hgher heat flux n the metallc layer atop of the oxde layer. The decay power transported to the top accounts ~63% of the total power nput from the LIVE-3D results and even ~77% from LIVE-2D results. These values are hgher than observed n other studes. The hgh ward heat transfer from LIVE test results provdes therefore a new nsght and requrement for the examnaton of the establshed -Ra correlatons obtaned from dfferent Ra range, smulant materal and/or heatng method. LIVE-2D test results have smlar melt temperature and heat flux dstrbuton characterstcs as LIVE-3D results. The maxmum heat flux s about tmes of the mean heat flux. Water has generally lower heat transfer coeffcent than molten salt both to the top surface and to the curved vessel wall. Also the proporton of the lower stable zone to the per well-mxed zone s dfferent as salt pool. The reason could be the dfferent Prandtl number of the smulant materal. 5 REFERENCES [1] B. Sehgal and T. Dnh, "In-vessel melt retenton (IVMR) as a severe accdent management (SAM) Strategy," n Severe accdent phenomenology short course, Cadarache, [2] V. Asmolov, S. Bechta, V. Khabensky, V. Gusarov and V. Vshnevsky, "Parttonng of U, Zr and FP between molten oxdc and metllc corum," n MASCA Project ( )/Vol.1. Proc. of the MASCA Semnar, June 2004, Ax-en-Provence, France, [3] V. Asmolov, S. Abaln, A. Surenkov, I. Gndo and V. Strzhov, "Results of Salt Experments Performed durng Phase I of RASPLAV Project, RP - TR - 33," Russan Research Centre, [4] J. Bonnet and J. Seler, "Thermal hydraulc phenomena n corm pools: the BALI Experment," n 7th ICONE, Tokyo Japan, [5] M. Jahn and M. Renecke, "Free convecton heat transfer wth nternal heat sources calculatons and measurements," n Proceedngsof the 5. Internatonal Heat Transfer Conference, Vol. 3, p. 74, [6] G. Kolb, S. Theerthan and B. Sehgal, "Experments on n-vessel melt pool formaton and convecton wth NaNO3-KNO3 salt mxture als smulant," n Proceedngs of ICONE 8, Baltmore, USA, [7] T. Theofanous, C. Lu, S. Addton, S. Angeln and O. Kymlnen, "In-vessel coolablty and retenton of a core melt," clear Engneerng and Desgn (1997) 1 48, vol. 169, pp. 1-48, [8] T. Theofanous, M. Magure, S. Angeln and T. Salmass, ""The frst results from the Sesson 2, paper /14 pages

14 6 th European Revew Meetng on Severe Accdent Research (ERMSAR-2013) Avgnon (France), Palas des Papes, 2-4 October, 2013 ACOPO experment"," clear Engneerng and Desgn, vol. 169, pp , 1997 ACOPO. [9] X. Gaus-Lu, A. Massoedov, T. Cron, B. Fluhrer, S. Schmdt-Stefel and T. Wenz, "test and smulaton results of LIVE-L4 +LIVE-L5L", KIT Scentfc publshng, [10] B. Fluhrer, A. Masoedov, X. Gaus-Lu and T. Cron, "Experement n the LIVE-2D test faclty at KIT on melt behavor n RPV lower head," n reth15, [11] X. Gaus-Lu, B. Fluhrer, T. Cron and T. Wenz, "Frst results n the LIVE-2D test faclty at KIT on melt behavour n RPV lower head," n Jahrestagung Kerntechnk, Stuttgart, [12] F. Kretzschmar and B. Fluhrer, "Behavor of the Melt Pool n the Lower Plenum of the Reactor Pressure Vessel -Revew of Expermental Programs and Background of the LIVE Program," Forschungszentrum Karlsruhe, [13] A. Massoedov, T. Cron, J. Fot, X. Gaus-Lu, S. Schmdt-Stefel and T. Wenz, "LIVEexperments on melt behavor n the RPV lower head.," n Proceedngs ICONE-16, Orlando, [14] X. Gaus-Lu, A. Massoedov, J. Fot, T. Cron, F. Kretzschmar, A. W. T. Palagn and S.- S. S., "LIVE-L4 and LIVE-L5L Experments on Melt Pool and Crust Behavor n Lower Head of Reactor Pressure Vessel," clear Technology, Vols. 181, Nr.1, pp , [15] X. Gaus-Lu and A. Massoedov, "LIVE Expermental results of melt pool behavour n the PWR lower head wth nsulated per ld and exernal coolng," n ICONE21, Chengdu, [16] X. Gaus-Lu, A. Massoedov, B. Fluhrer, T. Cron, J. Fot, S. Schmdt-Stefel and T. Wenz, "KIT Scentfc reports 7542"Results of the LIVE-L3A Experment"," KIT Scentfc publshng, Karlsruhe, [17] B. Sehgal and Z. Yang, "Ex-Vessel Core Melt Stablzaton Research: On the Experments wth Smulant Materals at KTH," KTH, Stockholm, Sweden, [18] F. Asfa and V. Dhr, "An expermental study of natural convecton n a volumetrcally heated sphercal pool bounded on top wth a rgd wall," clear Engneerng and Desgn, vol. 163, pp , [19] F. Maynger, M. Jahn, H. Reneke and U. Stenberner, "Untersuchung thermohydraulscher Vorgänge sowe Wärmeaustausch n der Kernschmelze," Bundesmnsterum für Forschung und Technologe, [20] B. R. Sehgal, "clear safety n lght water reactors", Elsever, ISBN: , 2012, p Sesson 2, paper /14 pages