Dalle Donne, M.

Dorner, S.

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KfK 3088EUR 7050eDezember 1980Measurements of Density andof Thermal ExpansionCoefficient of SodiumTetraborate {Borax)-U02 and ofSodium Metaborate-U02SolutionsM. Dalle Donne, S. DornerInstitut für Neutronenphysik und ReaktortechnikProjekt Schneller BrüterKernforschungszentrum Karlsruhe .KERNFORSCHUNGSZENTRUM KARLSRUHEInstitut für Neutronenphysik und ReaktortechnikProjekt Schneller BrüterKfK 3088EUR 7050eMeasurements of density and of thermal expansioncoefficient of sodium tetraborate (borax)-U0 2 andof sodium metaborate-U0 2 solutionsby~)M. Dalle Donne and S. Dorner.)Delegated from Euratom to the Karlsruhe NuclearResearch Center, Institute for Neutron Physics andReactor EngineeringKernforschungszentrum Karlsruhe GmbH, KarlsruheAls Manuskript vervielfältigtFür diesen Bericht behalten wir uns alte Rechle vorKernforschungszenIrum Karlsruhe GmbHISSN 0303-4003AbstractMeasurements have been performed of the density and volumetricthermal expansion coeff}cient of liquid sodium tetraborate(borax) and of sodium metaborate both pure and with twodifferent amounts of U0 2 dissolved in each. These data arerequired for the design of core-catchers based on sodiumborates. The measurements have been performed with the buoyancymethod in the temperature range from 8500 C to 13250 C. The datafor the pure borax and for the sodium metaborate agree reason-ably well with the data from the literature, giving confidencethat the measurements are correct and the new data for thesalts with U0 2 are reliable.Messungen der Dichte und der thermischen Ausdehnungskoeffizientenvon Natriumtetraborat (Borax)-U0 2 und von Natriummetaborat-u0 2Lösungen.ZusammenfassungEs wurden Messungen der Dichte und der kubischen Ausdehnungs-koeffizienten von reinem Natriumtetraborat (Borax) und Natrium-metaborat sowie deren Mischungen mit zwei verschiedenen Mengenvon U02durchgeführt. Diese Werte sind für die Auslegung einesKernschmelzenauffängers (Core-Catcher) erforderlich. Die Mes-sungen wurden mit der Auftriebsmethode im Temperaturbereich von850 0 C bis 13250 C vorgenommen. Die erhaltenen Werte der reinenStoffe stimmen gut mit den Literaturwerten überein und darausist zu schließen, daß die Werte der Mischungen auch zuverlässigsind.- 1 -1. IntroductionSodium borates appear to be quite suitable as sacrificialmaterials for a core-catcher of a nuclear reactor. U02, PU02and the fission product oxides, contained in the core debrisresulting from a hypothetical accident, will be dissolved bythe sodium borates of the core-catcher, placed on the base ofthe cavity containing the core, provided they remain in con-tact for a sufficiently long time at sufficiently high tempera-tures. The core catcher is made up of a matrix of higher mel-ting point material, formed by thin boxes containing the sodiumborates. In this way the supporting structure in the catcherconsists of a material which fails at higher temperatures, andsufficiently high temperatures are available for the borate todissolve the oxides.The studies and investigations in the Karlsruhe Nuclear ResearchCenter forsee the use of sodium tetraborate (borax, Na 20.2B20 3 =Na 2B40 7 ) and/or of sodium metaborate (Na20'B20 3 = 2NaB0 2 ) /1-4/.Borax has the advantage of a higher boiling point and it is lesschemically aggressive; sodium metaborate dissolves the oxidesmore readily.The calculations of the temperatures and heat fluxes at thewalls of the sodium borate melt containing in solution U0 2 ,Pu0 2 and the fission product oxides after an hypotheticalaccident involving the whole core of a 1000 MWe fast reactorhave been performed either assuming the physical propertiesof the pure sodium borate or the effect of the large quanti-ties of dissolved U0 2 has been estimated by comparison withother glasses /3/. These assumptions are however too roughand the results of the thermal calculations are affected bya considerable degree of uncertainty. In particular informa-tion is required on:- 2 -density and volumetrie expansion coefficient of liquidborax and sodium metaborate containing defined amountsof dissolved U0 2- viscosity and thermal conductivity for the same materials.The results of our laboratory experiments to determine densityand volumetrie expansion coefficients of liquid borax andsodium metaborate containing defined quantities of dissolved UO 2are given in the present paper. Measurements of the viscosityof the same materials have been started at the Karlsruhe NuclearResearch Center. The measurements of thermal conductivity willbe part of our future programme.2. Experimental Apparatus and Data EvaluationThe measurements performed during the present experiment wereessentially measurements of the density, and thus of its in-verse the specific volume, of a liquid at various temperatures.The variation of the specific volume with temperature is ofcourse the volumetrie expansion coefficient. Various systemshave been suggested to perform these measurements /5/, howeverthe requirement to operate at relatively high temperatures(850-1300oC) has dictated the choice of the measurement system:the so-called buoyancy system. This method allows a continuousmeasurement of the density and the determination of the tempera-ture is precise and simple. The buoyancy method has often beenused to measure the density of molten salts /6/.Fig.1 shows schematically the experimental apparatus. One panof aprecision balance has been replaced by a sinker of knownweight attached to the bar of the balance by means of long wire.In our experiment we used a platinum sinker about 25 mm longand weighing 42.4721 g, attached to a 440 mm long wire alsoof platinum. During the experiments the sinker and a small- 3 -portion of the wire are imrnerged in the molten salt, whosedensity has to be measured. The molten salt is eontained ina platinum erucible, form and dimensions of which are givenin Fig.1. The volumetrie capacity of the crucible is about115 em 3 . During the tests the volume occupied by the maltensalt and by the sinker was about 80 cm3 . The crucible wascontained in an electrically heated furnace. By varying theheating power, it was possible to obtain various temperaturelevels in the furnace. The temperature was measured by aplatinum/platinum-rhodium (18%) thermacauple imrnerged in themolten salt. The measurements were performed at temperatureintervals of 25 0 C. After each power variation to obtain an-other temperature level, the measurement was perfarmed whennew stationary temperature conditions in the furnace wereachieved, as indicated by the thermocouple reading.For Archimedes' principle the density of the liquid containedin the crueible is given by:(1)where:Ml= mass of the liquid displaeed by the sinkerMpt= total mass of the platinum sinker (Mpts ) andplatinum wire (Mptw)Mpt1= mass of the sinker and plantinum wire imrnersedin the liquidppt(T)= density of platinum as a function of temperatureMpt-M l = balance reading at equilibrium- 4 -Experiments were performed with six different type of moltensalts (s. Table I at the end of the paper). For the first testswith pure borax a thinner wire was used. Mpt and Mare knownPt1by weighing sinker and wire before the measurements and re-cording the small portion of the wire which is immerged duringeach experiment (see Table I). Mpt-Ml is given by the balancereading at equilibrium. The density of platinum as a functionof temperature was obtained from reference /7/ and it is givenin Table 11. Equation (1) allows therefore the determinationof the density of the liquid saltoAfter the experiments were performed, it was observed that thesolidified melt of borax containing 15.8% U0 2 presented twoweil separated regions: one yellow and one green (see Fig.2)It was therefore feared that a separation in two regions withdifferent U0 2 concentrations had taken place. Similar, if lesspronounced separation of regions were observed with the meta-borate-U0 2 sampies (Fig.3 and 4). The sampies were thereforesubjected to a X-ray fluorescence analysis with an EXAM-MAXsystem for the determination of the uranium distribution inthe sampies. It was found that the uranium is uniformlydistributed within the accuracy of the instrument (10%). Thedifferent colour and the phase separation is likely due tothe presence in the U0 2 of two slightly different oxidationdegrees. It is indeed known that a borax bead containinguranium oxide is orange-yellow in the oxidation flame andgreen in a reduction flame /8/.3. Experimental ResultsTables 111 to VIII give the experimental results for the sixseries of experiments: one with pure borax, one with puremetaborate and the others with two different amounts of dis-solved U0 2 in each. The Tables show the balance reading andthe value of Pi calculated with equation (1), the other para-meters being obtained for each series from Tables I and 11.- 5 -Figures 5 and 6 show the same data in the plot density PIversus temperature T, for borax and sodium metaborate re-spectively. The agreement of the borax density with a valueat 10000C from the literature /9/ is relatively good,(difference = 1.7%). Figures 7 and 8 show the variation ofdensity with the amount of dissolved U02at eonstant tempera-tures.Once the density is known, the speeifie volume of the moltensalt vI ean be obtained by the equation:(2)and the coeffieient 6 of volumetrie thermal expansion is de-fined by equation (3):(3 )where T is the temperature in °c and Vo the specifie volumeof the molten salt, if it were still liquid, at OoC.oFrom Figures 5 and 6 it ean be seen that up to 1200 C thevariation of PI with temperature is approximately linear.The same ean be said of vI' and thus the value of 6 is aconstant up to 12000 C for eaeh molten salt investigated.Table IX and Fig.9 show these constant values of 6, validup to T=1200 0 C, obtained with equation (3). For pure borax-4 0 -1one has 6=3.83 x10 C. This value ean be compared withthe value obtained by Volarovieh by direet measurement ofthe volume change with temperature:in the temperature rangeo 0 -40 -1from 859 C to 1305 C 6 is equal to 2.6x10 C /10/ asquoted in the referenee /11/. The definition of 6 used inthis relatively old paper is however different from ours.Volarovieh uses the definition of 6:V(T=1305 0 C)-v(T=8590 C) =v (T=859 0 C) (1305-859)(4)A value ofß = 3.35 x- 6 --4 0 -1ßv = 2.6x10 e corresponds to a value of10-4 oe with our definition. Thus the differencebetween our value of ß and that of Volarovich is only 12.5%.Fig.10 shows the specific volume of pure sodium metaborateas a function of temperature. The Russian data obtained witha direct measurement of the volume increase with temperature/11/ lie about 2.3% higher than our data. The coefficient ofthermal expansion ß is, with our definition, equal to4.73x10-4 °e-1 (with the Russian data definition ßv=3.2X10-4 °e-1)against 4.49x10-4 °e- 1 , the difference being 5.3%.AcknowledgementsThe authors gratefully acknowledge the help of K. Schorband E. Simon, who carried out the measurements, and ofMrs. I. Schub and Mr. G. Schumacher, who performed thex-ray fluorescence analysis.- 7 -References/1/ M. Dalle Donne, S. Dorner and G. Schumacher:Preliminary design of a borax internal core-catcher fora gas-cooled fast reactor, KfK 2352, EUR 5505e, September1976./2/ M. Dalle Donne, S. Dorner and G. Schumacher:Development work for a borax internal core-catcher fora gas-cooled fast reactor, Nuclear Technology, l1, 138-155, July 1978./3/ M. Dalle Donne, S. Dorner, G. Fieg, G. Schumacher andH. Werle:Development work for fast reactor core-catchers on thebasis of sodium borates, Proc. ANS-ENS Int. Meet. on FastReactor Safety Technology, Seattle, Washington, August19-23, 1979./4/ M. Dalle Donne and H. Werle:Laboratory studies of the meltfront propagation in aborax core-catcher, KfK 3021, August 1980./5/ H. Harms:Die Dichte flüssiger und fester Stoffe. Friedr. Vieweg& Sohn Braunschweig, 1941./6/ A.I. Beljajew, E.A. Shemtschushina und L.A. Firsanowa:Physikalische Chemie geschmolzener Salze. VEB DeutscherVerlag für Grundstoffindustrie, Leipzig, 1964./7/ P.T.B. Shaffer:No.1 Materials Index, Plenum Press Handbooks of High-Temperature Materials, Plenum Press, New York, 1964.- 8 -/8/ F.P. Treadwell:Kurzes Lehrbuch der analytischen Chemie. I. Band.Qualitative Analyse, S.151, Franz Deuticke, Leipzigund Wien, 1930./9/ P. Pascal:Nouveau Traite de Chirnie Minerale, Tome 11, p.l014,Masson et Cie, Paris, 1966/10/ M.P. Volarovich, Jzv. Akad. Nauk SSSR 1933 663/74;Acta Physicochim. URSS ~, 1935, 695/710, 702./11/ M.P. Wolarowitsch and A.A. Leontjewa:Bestimmung des spezifischen Volumens von Schmelzenbei Temperaturen bis zu 1400oC, Z. Anorg. Allgern.Chem. 225, 1935, 327-332.Table I: Test conditionsTest series Type of sodium Quantity of Quantitiy of Weightnumber borate sodium borate dissolved percentage Mpts Mptw Mpt1(g) U0 2 (g) of dissolvedU02(g) (g) (g)1 150 - 0% 1.9913 42.52642 borax 149.84 12.77 7.9% 42.54193 151.06 28.39 15.8% 42.4721 2.5609 42.64674 150 - 0% 42.54195 sodium 148.569 15.323 9.3% 42.54196 metaborate 147.538 30.601 17.2% 42.6467'"- 10 -Table 11: Platinum density /7/T (oC) ppt(T) (g/cm3 )850 20.905875 20.89900 20.87925 20.86950 20.84975 20.831000 20.811025 20.791050 20.781075 20.761100 20.751125 20.731150 20.721175 20.701200 20.681225 20.671250 20.651275 20.641300 20.621325 20.61- 11 -Table 111: Density of pure sodium tetraborate (borax)T Mpt-MI PI(oC) (g) (g/cm3 )850 40.2203 2.086875 40.2581 2.066900 40.2735 2.056925 40.3013 2.042950 40.3250 2.028975 40.3446 2.0171000 40.3643 2.0061025 40.3944 1.9891050 40.4122 1 .9801075 40.4423 1 .9631100 40.4643 1 .9511125 40.4822 1 .9411150 40.5105 1 .9261175 40.5368 1 .9111200 40.5643 1 .8961225 40.5834 1 .8861250 40.6205 1 .8661275 40.6533 1 .849- 12 -Table IV: Density of borax with 7.9% U0 2T Mpt-M1 P1(aC) (g) {g/cm3875 40.5460 2.203900 40.5700 2.189925 40.5920 2.178950 40.6215 2.161975 40.6390 2.1511000 40.6615 2.1381025 40.6760 2.1291050 40.6970 2.1181075 40.7260 2.1021100 40.7440 2.0921125 40.7625 2.0811150 40.7810 2.0711175 40.8010 2.0591200 40.8235 2.0461225 40.8440 2.0351250 40.8590 2.026L-._______- 13 -Tab1e V: Density of borax with 15.8% U0 2T Mpt-M1 °1(aC) (g) (gjcm3 )975 40.3059 2.3091000 40.3085 2.3051025 40. 311 5 2.3021050 40.3140 2.2991075 40.3170 2.2961100 40.3200 2.2931125 40.3250 2.2881150 40.3280 2.2861175 40.3315 2.2821200 40.3350 2.2781225 40.3380 2.276- 14 -Tabie VI: Density of pure sodium metaborateT Mpt-Mi Pi(aC) (g) 3(g/cm )975 41.0330 1 .9591000 41.0565 1. 9451025 41.0795 1 .9321050 41.1035 1. 9191075 41.1235 1 .9081100 41.1445 1 .8971125 41.1670 1 .8841150 41. 2061 1 .8641175 41.2255 1 .8531200 41.2515 1 .8381225 41.2820 1 .8231250 41.3225 1 .8011275 41.3525 1 .7861300 41 .3900 1 .7661325 41.4410 1 .740- 15 -Table VII: Density of sodiurn metaborate with 9.3% U02T Mpt-M1 P1(oC) (g) (g/cm3 )950 40.959 1.996975 40.979 1.9851000 41.0160 1 .9651025 41.0410 1 .9511050 41.0630 1 .9391075 41.0830 1.9281100 41.1020 1 .9171125 41.1270 1 .9031150 41. 1 520 1.8901175 41. 1 820 1 .8741200 41.2100 1 .858Table VIII: Density of sodiurn metaborate with 17.2% U0 2T Mpt -M1 Pl(aC) ( g) (g/cm3 )950 40.4720 2.229975 40.4840 2.2221000 40.4970 2.2131025 40.5100 2.2051050 40.5230 2.1981075 40.5360 2.1901100 40.5510 2.1811125 40.5660 2. 1711150 40.5810 2.1631175 40.5950 2.1 541200 40.6080 2.146- 16 -Table IX: Thermal expansion coefficient ß up to 12000 CTest series Type of salt tested ß 10 4 (Oe-I)xnumber1 pure borax 3.832 borax with 7.9% U0 2 2.953 borax with 15.8% U0 2 0.624 pure sodium metaborate 4.495 sodium metaborate with 4.179.3% U0 26 sodium metaborate with 1. 8217.2% U0 2- 17 -BALANCEg-~=><7~1 t;~;5\THERMAL SHIELD WIREPLATINUM SliNNiKKEERP~~~S88888~§- 5840DIMENSIONS OFTHE PLAT1NUMCRUCIBLE INMILLIMETERSFURNACETHERMAL INSULATIONMOLTEN SALT-,~~\-CRUCIBLE-- PL.-RH. THERMOCOUPLEFig.1: Schematical arrangement of experimental apparatus- 18 -Fig.2: Test sampIe: borax with 15.8% U0 2- 19 -Fig.3: Test sample: sodium metaborate with 17.2% U0 2Fig.4- 20 -Test sample: sodium metaborate with 9.3% U02'--.-.IV~•~•~•••~•~:>t- 2.1-(/)ZW 2.0oI I 2 3(Y') .Eo........ 2.2I 0),1.91.8.&. SODIUM TETRABORATE (BORAX)o 7.9Wt% U02 , REST BORAXG 15.8 Wt % U02 , REST BORAXo BORAX [PASCAL, REF. 9]13001.7 ' I!! I ,800 900 1000 110U lLUUTEMPERATURE oeFig.5: Density of borax, and of borax with U0 2 versus temperature8 SODIUM METABORATEo 9.3 Wt % U02 J REST SODIUM METABORATE817.2Wt% U02 J REST SODIUM METABORATE1.7I I(Y) 221E•"""'1:.1U~........Cl 2.1---..:., ,~ •:>I- 2.0 I-(/).....z IW 1.9Cl~~- .1.8I '"'"1. 6 I ! I ! I ! I I800 900 1000 1100 1200 1300TEMPERATURE oeFig.6: Density of sodium metaborate and of sodium metaborate withU0 2 versus temperature.'"w1000 0 C11 00 ° C1200 0 C----0----_._.-/!:r._.---E]f----...........",~:.r,", . ..// ./..",/ ./fiJ"'/ ./",,,,, /.//'" K'// /'..,.../ /"/./2.0"1.9.·>- 2.2....VizW 2.1Cl'-(Y)------.E~ 2.3, Cl ,1.820%15%10 %5 %I I1.7 I ! ! !0 %WEIGHT PERCENTAGE OF U02 IN BORAXFig.7: Density of borax-uo 2 as a function of percentage of U0 2 atvarious temperatures'M ,2,3EU"'", Cl 2.2,>-I- 2.1-(f)ZW 2.0Cl•1.9~._._._._._._.~·/•1.8-.-. -0-._.- 1000 ° C----&---- 1100 0 C----1[:=::1 1200° CIV..,.15%10%5%1. 7 I I I I ! I0%WEIGHT PERCENTAGE OF U02 IN SODIUM METABORATEFig.8: Density of sodiurn metaborate-u0 2 as a function of percen-tage of U0 2 at various temperatur es- 25 -• SODIUM TETRABORATE (BORAX).. SODIUM METABORATE.....IU 50...;r0-)(C!l.321o0"10 5"10 10 "10 15 %Fig.9: Coeffieient of volumetrie thermal expansion as a funetionof U0 2 pereentage- 26 -0.58 .--------,------r----,....--------,-I1100 1200 1300TEMPERATURE (OC)1000A PRESENT RESULTSEI DATA FROM REF. [11]0.519000.530.540.520.55-->i Ol'"" 0.57('t')E, u '0.56Fig.10: Specific volume of sodium metaborate versus temperature

Measurements of density and of thermal expansion coefficient of sodium tetraborate (borax)-UO₂ and of sodium metaborate-UO₂ solutions

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Measurements of density and of thermal expansion coefficient of sodium tetraborate (borax)-UO₂ and of sodium metaborate-UO₂ solutions

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