PHYSICAL PROPERTIES MEASUREMENTS WITHIN MASCA PROJECT. Asmolov V.G., Abalin S.S., Merzlyakov A.V. Russian Research Centre KURCHATOV INSTITUTE

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1 PHYSICAL PROPERTIES MEASUREMENTS WITHIN MASCA PROJECT. Abstract Asmolov V.G., Abalin S.S., Merzlyakov A.V. Russian Research Centre KURCHATOV INSTITUTE Measurements of corium physical properties started within of RASPLAV project have been continued within MASCA project. Experimental data on viscosity, density and liquidus temperature of C-32 corium are presented in report. Within MASCA project the phenomenon of uranium and zirconium extraction was found at interaction of molten corium and metal iron. The melt is stratified on oxide and metal parts. Physical properties of the metal part were studied within MASCA project. The experimental data on conductivity, thermal conductivity, viscosity and liquidus temperature of metallic body are presented in report. 1

2 Introduction Within the context of the OECD MASCA project, the works on the measurement of the corium physical properties started under the RASPLAV project were proceeded. Physical properties of the metallic body, the alloy produced on the suboxidized corium interaction with steel (iron), were measured too. This report presents the results of the corium C-32 viscosity and density measurements and data on the measurements of electric conductivity, thermal conductivity, viscosity and temperatures for phase transients. Viscosity of the c-32 corium The method of damping of torsional oscillation of a cylinder filled with studied liquid was employed for the measurement of viscosity as it was in the OESD RASPLAV project. The technique theoretical basis, the procedures for the test performance and for the experimental data processing were described earlier [1]. Figure 1 illustrates the test facility layout. Figure 2 demonstrates the example of the test thermogram Figure 1. The Test Facility Layout Vessel 2 Heater 3 Inductor coil 4 Support 5 - Corium 6 Cylinder 7 Rod 8 Diaphragms 9 Mirror 10 Laser He-Ne 11 Scale 12 Thread 13 Windows 14 - Pyrometer

3 Figure 2. The Example of the Test Thermogram on the Measurement of Viscosity Temperature (oc) Time (min) Experimental Results Figure 3 shows the damping decrement of the torsional vibrations of the cylinder with a molten corium versus the temperature. Up to 2200 C (Figure 3 does not show this area), the system behaves as a solid body and is characterized by a low damping factor that is practically independent of the temperature. Under the temperatures higher than 2370 C, the system is characterized by a high damping factor that is slowly decreased with the temperature increase. This behaviour is typical of normal liquids. Within the temperature range C, the system is characterized by a noticeable growth of the damping factor with the temperature increase. This temperature range may be considered as a simultaneous existence of a solid and liquid phases. Figure 3. The Damping Decrement versus the Temperature Dec* Temperature ( o C) 3

4 The values were calculated for the corium C-32 kinematic viscosity under the temperatures higher than 2370 C. Figure 4 presents the kinematic viscosity versus the temperature. Figure 4. The Kinematic Viscosity versus the Temperature V*E6 (m 2 /s) Temperature ( o C) It should be noted that the obtained dependence is very close to that measured earlier for the C-22 corium [1]. Conclusion The C-32 corium kinematic viscosity was measured within the temperature range C. The obtained dependence is close to that measured earlier for the C-22 corium. Density of the C-32 Corium A modification of the hydrostatic weighing method called the submersible cylinder method was chosen to measure density. The Test Facility Figure 5 illustrates the test facility layout. 4

5 Figure 5. The Test Facility Layout The corium (3) was placed into the tungsten crucible (2). The crucible was covered with a tungsten cover with a pipe the end of which came out into the facility cold area. A tungsten cylinder (4) was hanged in the crucible above the corium. The upper part of the pendant consisting of a thin tungsten rod (5) and metal wire (14) was attached to the platform of the electronic scales (16). The weight measurement accuracy was 5 mg. A microprocessor was installed into the scales that allowed to record their readings in the computer. The scales protective shielding (15) and the facility casing were conjugated through the hermetic seal (13). The scales protective shielding (15) with the scales inside could move relative to the facility casing (1). Their relative positions might be noted at the scale (12) accurate to 0.05 mm. The crucible with the corium was placed on the support (9) inside the heater. The crucible bottom temperature was measured by a pyrometer. A thermostating embedding (7) of a high thermal conductivity was attached around the heater to reduce the temperature gradients. The whole facility was enclosed by a thick layer of thermal insulation (8). The Test Procedure and Results At the test beginning, the tungsten cylinder position was chosen to be above the melt level. Then, the protective shielding with the scales inside went down with a pitch of one millimeter. At each position of the scales, the difference between the initial cylinder weight and the current one was noted. Figure 6 demonstrates the example of this dependence. 5

6 Figure 6. Dependence of the Difference between the Initial Value for the Cylinder and Pendant Weight and the Current Value of that at Each Position of Scales dm (g) H (mm) The change in the weight is not observed in the course of the scales relocation when the tungsten cylinder bottom does not touch the melt surface (Scale divisions higher than 26 mm correspond to this case in Figure 6). A drastic increase in the weight due to the corium surface tension forces is observed on the cylinder bottom touching the melt surface. On the further cylinder immersion into the melt, the cylinder weight is linearly decreased with the immersion depth due to the buoyancy force. The inclination of line was determined by the least-squares method. The melt density was calculated by the following formula: 1 1 dm ρ = s s dx 1+ SC s P0 P( h) dm ( h) = g where: ρ - density; S the cylinder cross-section area; S C the crucible cross section area; P 0 the cylinder weight in argon; P(h) the cylinder weight immersed in the depth h; X cylinder position. The measurements were performed at several temperature values. Table 1 presents the obtained results. Table 1. The C-32 Corium Density Temperature ( o C) Density (g/cm 3 ) Dispersion (g/cm 3 )

7 The C-32 corium surface tension was measured earlier within OECD RASPLAV project. Simultaneously, the melt density might be evaluated. The following value for density 7.49 ± 0.44 g/cm 3 was obtained from the data of the surface tension measurement. Conclusions The facility was developed, designed and fabricated to measure density of high-temperature melts. The facility operating temperatures ranges up to 2700ºC. The test facility, procedures of the measurement and data processing were tested in the experiments with water. Measured water density coincides with the tabular data. Dispersions are less than the experimental errors. Data on the C-32 corium density were obtained within the temperature range ºC. C-32 Corium Liquidus Temperature Measurement Several techniques can be used to measure liquidus temperature of corium. These techniques have been developed within OECD RASPLAV&MASCA projects Viscosity technique Gas bubble technique Thermogram recording technique. The example of liquidus determination by viscosity technique is presented in Figure 7. Figure 7. Decrement vs Temperature (62UO2 + 38ZrO2 mol%) Decrement 1000 Liquidus temperature o Temperature ( C) The facility schematic for liquidus measurement by gas bubble technique is presented in Figure 8. 7

8 Figure 8. Gas Bubble Technique: Test Section 1.Vessel; 2.Tungsten crucible; 3.Corium; 4.Capillary; 5.Guide; 6.Heater; 7.Thermostat; 8.Thermal insulation; 9.Support; 10.Peep hole; 11.Pyrometer; 12.Scale; 13.Pressure-gauge; 14.Ar-admission valve; 15.Sealing unit. The dependence of pressure vs. temperature is presented in Figure 9. Figure 9. Gas bubble technique: Pressure vs. temperature. (54.5UO ZrO Zr) 9 8 Pressure (kpa) Liquidus Temperature ( o C) 8

9 Figure 10. Comparison of Liquidus Measurement by Three Different Pressure Decrement Pressure (kpa) 6 Decrement 0.08 dt/dτ dt/dτ ( o C/s) Technique Temperature ( o C) As one can see three different techniques gave very close results. The Choice of the Material for the Metallic Body Melt Retention The choice of the material for the metallic body retention presents quite a complicated problem. The thing is that such metals as iron and zirconium are parts of the metallic body composition. Iron interacts practically with all metals and alloys that makes it problematical to employ metal crucibles. Free zirconium is a very active metal that interacts with oxides. On measuring the metallic body electric conductivity, it was noted that the alloy electric conductivity was close to zirconium one. This situation is possible if the alloy components containing iron were included into the metal matrix based on zirconium. Figure 11 demonstrates photographs of the alloy structure after the MA-2 test. Figure 11. Photographs of the Alloy Structure after the MA-2 Test мкм 20 мкм The light phase is the phase based on zirconium, the dark one is based on iron. It can be seen that the dark phase is enveloped by the light phase. This alloy structure allows to hope that the same materials that are used for the retention of metal zirconium may be used for the melt retention. At the initial stage of the zirconium metallurgy development, graphite was employed for melting of that. Molten zirconium interacts with graphite surface producing on that a layer of zirconium carbide, which hinders transport of carbon atoms to the metal zirconium melt. 9

10 We employed crucibles made of graphite with density higher than 1.7 g/cm 3. The crucible was preliminary cladded with zirconium carbide produced on molten zirconium interaction with graphite surface. With graphite density less than 1.64 g/cm 3, crucibles appeared to be with open porosity and metal zirconium infiltrated the whole volume of the graphite wall. With graphite density higher than 1.68 g/cm 3, zirconium carbide was generated only on the inner surface of the graphite crucible. Figure 12 shows photographs of the graphite crucible cross-sections after melting of the metallic body alloys in them. The first photograph shows the crucible after melting of the metal body sample produced in the T-7 test. The second one shows the crucible with a large volume of the metallic body (U 0.44 Zr 0.56 ) 0.2 Fe 0.8 synthesized artificially from pure metals. Gross formula of the synthesized body coincides with the gross formula obtained from the chemical analysis of the metallic body after the T-7 test. The visible destruction of the graphite crucible wall by the metallic body melt was not observed in both tests. The third photograph presents an enlarged scale of a part of the boundary between the metallic body and graphite wall. Figure 12. Photographs of the Graphite Crucible Cross-Sections after Melting of the Metallic Body Alloys in Them Crucible with T-7 Alloy Crucible with (U0.44Zr0.56) 0.2 Fe0.8 Alloy The Boundary Area The performed tests have shown that crucibles made of dense graphite covered with zirconium carbide protective claddings may be used for the retention of the metallic body melt. The Metallic Body Solidus and Liquidus Temperature Measurements The method based on the investigation of thermograms obtained on heating and cooling of the sample under study was used for the measurement of the phase transfer temperatures. Alloys prepared artificially from pure metals were used to work through the technique and perform the first tests. Figure 13 demonstrates the example of thermogram obtained on cooling Zr 0.25 Fe 0.75 melt. 10

11 Figure 13. The Thermogram Obtained on Cooling of the Zr 0.25 Fe 0.75 Alloy 1800 temperature ( 0 C) time (min) Two transitions where heat is released on cooling are seen distinctly. The image becomes still more obvious if it is represented in the coordinates time and temperature derivative with respect to time. Figure 14 illustrates the example of the similar dependence of the same Zr 0.25 Fe 0.75 alloy. Figure 14. Temperature Derivative versus Temperature of the Zr 0.25 Fe 0.75 Alloy dt/dt (mk/sec) temperature ( 0 C) The observed transition temperatures coincide with a good accuracy with the data of the known phase diagram Zr-Fe. The metallic body sample produced in the T-7 test was available for the team investigating physical properties. Figure 15 shows the thermogram obtained on this sample cooling. 11

12 Figure 15. The Thermogram Obtained on the T-7 Sample Cooling dt/dt (mk/sec) temperature ( 0 C) Only one phase transition was revealed in this sample within the temperature range ºC. To determine the U/Zr ratio impact on the liquidus temperature, several samples were fabricated from pure metals. A common gross formula may be expressed as (U x Zr 1-x ) 0.2 Fe 0.8 Figure 16 demonstrates the liquidus temperature versus the parameter X. This Figure presents data of other authors for the compositions Zr 0.2 Fe 0.8 [2] и U 0.2 Fe 0.8 [3] too. Figure 16. The Liquidus Temperature versus the Parameter X T (liq) Prepeared metallic body T-7 Metallic body R Ref. [1][6] R Ref. [2][7] Temperature ( o C) X One of the artificially fabricated samples had exactly the same U, Zr and Fe ratio as that in the T-7 test. However, it can be distinctly seen in Figure 16 that the liquidus temperature for the sample from the T-7 test is somewhat higher than that for the artificially fabricated sample of the same composition. This may be explained by the availability of small quantities of oxygen and carbon in the sample from the T-7 test. 12

13 The Metallic Body Viscosity Measurement The method of damping of torsional oscillation of a cylinder filled with the melt was used to measure the metallic body viscosity. Figure 1 illustrates the facility layout. Due to the fact that quite insufficient quantity of material produced on the corium and steel interaction was available for the researchers, viscosity was measured in the samples synthesized artificially from pure metals. Figure 17 shows the example of the thermogram from the test on viscosity measurement. Figure 17. Example of the Thermogram on Viscosity Measurement temperature ( 0 C) time (min) The measurements were performed at the stage of initial heating, at the stage of slow cooling and at the stage of reheating. The coincidence of the measurement results from all three stages testifies that the system is in the equilibrium state. The measurements were performed in the crucibles made of dense carbide cladded with zirconium carbide. Figure 18 presents the crucible cross-section after one of the tests. Figure 18. The Crucible Cross-Section after the Test on Viscosity Measurement 13

14 At the initial stage of investigations, viscosity of model compositions consisting of zirconium and iron was measured. Figure 19 shows viscosity versus the temperature for three model compositions with different contents of zirconium and iron. Figure 19. Viscosity versus the Temperature for Two Model Compositions with Different Contents of Zirconium and Iron 1 viscosity Fe-Zr Zr0.33Fe0.67 Zr0.25Fe Viscosity (m 2 /sec) temperature ( 0 C) It is seen that viscosity is decreased with the increase of the iron content. Viscosity of the compound containing uranium, zirconium and iron was measured. The gross formula of the composition (U 0.44 Zr 0.56 ) 0.2 Fe 0.8 is close to that of the sample produced in the T-7 test. Figure 20 presents the damping decrement versus the temperature. Up to the temperature 1380ºC, the system behaves as a solid body and is characterized by a low damping decrement. Under the temperature higher than 1600ºC, the system is characterized by a high decrement factor that does not practically depend on the temperature. This area may be construed as a liquid with a low fluidity activization energy. The intermediate area of ºC is characterized by the non-monotone behaviour of the damping decrement and may be construed as a two-phase area with simultaneous presence of the solid and liquid phases. Kinematic viscosity was calculated in the area of the theory applicability. Figure 21 illustrates kinematic viscosity versus the temperature. 14

15 Figure 20. The Damping Decrement versus the Temperature Decrement * temperature ( o C) Figure 21. The Metallic Body Viscosity versus the Temperature viscosity * 10 6 (m 2 /s) temperature (C) Electric Conductivity of the Metallic Body Produced on the Corium Interaction with Steel in the TULPAN-7 Test Electric conductivity is one of the most important characteristics of the material. The measurement of electric conductivity and its temperature dependence allows to judge about the nature of chemical linkage between the components of the studied material. The sample of mm 3 size cut out of the metallic body ingot obtained in the T-7 test was used for the investigation. Table 2 demonstrates the metallic body chemical analysis. 15

16 Table 2. The Metallic Body Chemical Analysis Element proportion (mass %) U/Zr U Zr (Zr+Fe+U) free Fe C Nb O (diff.) (at./at.) * * * - not measured The Method The four-probe method was employed in the work to measure electric conductivity. Figure 22 illustrates the method pattern. Figure 22. The Test Pattern Four electrodes are connected to the sample. They include two current ones by which direct current of the set value is transmitted through the sample and two voltage ones intended to measure the voltage drop in the sample part. The voltage drops for current several values were measured under the set temperature. The Volt-Ampere characteristic was plotted. Figure 23 illustrates this characteristic obtained in the test. 16

17 Figure 23. The Volt-Ampere Characteristic U (µv) I(A) The slope of that was determined by the least-squares method. The specific resistance was calculated by the formula du S ρ = di D where ρ - specific resistance; du/di the slope of the Volt - Ampere characteristic; S cross section area of the sample; D distance between voltage electrodes. The sample with electrodes connected to that was placed into a small heater to measure the temperature dependence of electric conductivity. The heater was surrounded outside by a thick layer of thermal insulation. The sample temperature was measured by a thermocouple. The Test Results Figure 24 demonstrates the ratio of specific resistance under the temperature t C to specific resistance under the temperature 20 C as a function of temperature. The linear growth of specific resistance is observed at the temperature rise. This dependence is typical of metals. The temperature coefficient for specific resistance was determined by the least-squares method. Table 3 presents the obtained values for specific resistance of the studied sample under 20 C and for the temperature coefficient of specific resistance. Figures in round brackets are the measurement errors (dispersion). The same table contains the corresponding values for pure iron [4], zirconium [5], and uranium [6] for the comparison. It is seen that specific resistance of the alloy under study is very close to that of zirconium and the temperature coefficient of specific resistance to that of uranium. 17

18 Figure 24. The Temperature Dependence of Specific Resistance R(t)/R(20) Temperature ( o C) Table 3. Specific Resistance (ρ) and Temperature Coefficient of that (α) of the Alloy and Its Components Material Alloy under study Referenc e T ( o C) ρ 10 8 (Ohm m) α 10 3 (1/K) (4.3) 2.38 (0.17) Fe [1] Zr [2] U [3] This work Conclusion Specific resistance and the temperature coefficient of that for the metallic body sample obtained in the T-7 test were measured. The measurements were performed within the temperature range C. The electric characteristics of the sample under study are similar to those of the metal ones. Specific resistance is very close to that of zirconium and the temperature coefficient of specific resistance to that of uranium. Thermal Conductivity of the Metallic Body Produced on the Corium Interaction with Steel in the TULPAN-7 Test Thermal conductivity of the metallic body produced on the corium interaction with steel in the T-7 test was measured. The same sample was employed for the measurements that was used to measure conductivity. Table 2 presents the metallic body chemical analysis. The Method Figure 25 demonstrates the pattern of measurements. 18

19 Figure 25. The Pattern of the Test on Thermal Conductivity Measurement The sample was placed between the heater and heat receiver. The heater and heat receiver were fabricated from copper to minimize the temperature gradients. The copper heater was heated by an electric coil. Four thermocouples were mounted in the assembly, that is, one on the heater, one on the receiver and two ones on the sample. Readings from thermocouples were memorized in the computer. The technique for thermal conductivity measurement is based on the solution of the non-steadystate equation: 2 T 2 T = a 2 t x with the initial condition and boundary conditions: λ T T (x,0) = T (0, t) = C T 0 F(t) dt r S = r + x dt x= L On meeting the following conditions: 2 dtr L dln(f(t)) Cs << Cr ; Cr >> QL; t > = t 0; t 0 << 1 dt π a dt the solution may be presented in form dtr D λ = Cr + QL dt S (T2 T3 ) where: a 2 - thermal diffusivity; λ - thermal conductivity; S - cross section area of sample; C r - thermal capacity of receiver; C s - thermal capacity of sample; Q L loses; T r - temperature of receiver; L - length of sample; D - distance between thermocouples. The Test Results Figure 26 demonstrates the example of readings from thermocouples. Q L 19

20 Figure 26. The Example of Readings from Thermocouples Temperature ( o C) Time (min) Figure 27 presents the sample thermal conductivity values calculated according to the test data. The tests were performed with the heater different power. It is seen that thermal conductivity does not practically depend on the temperature within the used temperature range. Table 4 presents the values obtained on processing the test data. Figure 27. The Values of Thermal Conductivity Obtained in Tests 16 Thermal conductivity (W/m/K) POWER of HEATER P=89 W P=35W P=44 W Temperature ( o C) 20

21 Table 4. Thermal Conductivity Data Obtained in Tests # P (W) T( o C) Thermal conductivity (W/(m K)) Number of experimental points Dispersion due to statistic (W/(m K)) Dispersion due to systematic error (W/(m K)) Total dispersion (W/(m K)) The table cites the following: the heater power P(W); the temperature range in which the technique is applicable; the average value for thermal conductivity; the number of experimental points; thermal conductivity dispersion determined by the statistics; thermal conductivity dispersion due to systematic errors (inaccuracy in the embedding of thermocouples, edge effects and so on); the estimate of total dispersion. At low power values (22 W) of the heater, thermal losses become of a significant matter. In this case, the technique underestimates the values of thermal conductivity and the statistical error is increased. For this reason, these results were not further used in the calculation of the average value of thermal conductivity given in the Table lower line. It is of interest to compare the obtained values for thermal conductivity of the sample under study with those of metals Fe, Zr, U composing the sample. Thermal conductivity of metals was taken from the reference book [7]. Figure 28 demonstrates graphically the similar comparison. 21

22 Figure 28. Thermal Conductivity of the Sample and Its Components 80 y ( ) Thermal conductivity Alloy [this work] U Ref.[4] Zr Ref.[4] Fe Ref.[4] o It is seen that thermal conductivity of the alloy is lower than that of any metal composing the alloy. Of all the metals, thermal conductivity of zirconium is the closest to that of the alloy. It should be noted that electric conductivity of the alloy is also close to that of zirconium. Conclusion Thermal conductivity of the metal body produced on the corium interaction with steel in the Tulpan-7 test was measured within the temperature range C. The value for thermal conductivity 13.5 W/(m K) was obtained accurate to (dispersion) 1.4 W/(m K). 22

23 References 1 S.S. Abalin, V.G. Asmolov, V.D. Daragan, Ye.K. D yakov, A.V. Merzlyakov, V.Yu. Vishnevskiy, Kinematic viscosity measurement of C-100 and C-22 corium. OECD RASPLAV Project, RP-TR-18, J. Nonorganic Chem., 8(9), 1963, pp (Russ). 3 Canad. Metallurg. Quart., 1966, 5(4), pp N.I. Koshkin, M.G. Shirkevich, Handbook on Elementary Physics, Moscow, Nauka, 1972, (Russ.) 5 V.E. Peletzkii, E.A. Belskaya, Electrical Resistance of Refractory Metalls, Moscow, Energoizdat, (Russ.) 6 J.J. Katz, E. Rabinovitch, The Chemistry of Uranium, v.1, NY, V.S. Chirkin, Thermo-physical properties of nuclear technics materials, Moscow, Atomizdat, 1968, (Russ). 23