Security and Privacy Notice Disclaimer

Viscosity of Liquid Uranium Dioxide

Viscosities of liquid uranium dioxide have been measured in the temperature range of 3143 to 3303 K by Woodley,¹ at the melting point (3120 K) by Palinski,² and from 3083 to 3328 K by Tsai and Olander.³ The recommended equation is that of Woodley because of the greater precision of his data and the agreement between Woodley and Palinski. The Woodley equation is:

Figure 1

where the kinematic viscosity, is in centipoise (mPa s) and T is in K. Recommended values are given in Table 1 as a function of temperature and graphed in Figure 1. The data of Woodley,¹ Palinski,² and Tsai and Olander³ as well as estimated uncertainties have been included in Figure 1.

The uncertainty in the available data is difficult to estimate because of the lack of high-temperature viscosity standards. For the temperature range of 3120 to 3400 K, the error is estimated as ± 25%. The uncertainty of extrapolated viscosities in the temperature range of 3400 to 4000 K is estimated as ± 50%.

Figure 2 shows the viscosity data of Woodley,¹ Tsai and Olander,³ and Palinski.² Tsai and Olander made measurements on two different samples. Their viscosities are higher than the values of Woodley and of Palinski and lack the precision of the data of Woodley. In addition, the Tsai and Olander data for the second sample are consistently higher than for the first sample, indicating a possible systematic error. Tsai and Olander gave the melting point of UO₂ as 3073 K (not 3120 K) so that their lowest temperature datum, 9.2 cP (mPa s) at 3083 K, is at a temperature that they consider to be completely liquid. They comment that their low melting point may be due to temperature measurement errors, change in stoichiometry of their samples, or contamination of their melt by the tungsten crucible. Figure 2 shows that Woodley's two series of measurements on the same encapsulated sample are in good agreement and in reasonable agreement with the datum of Palinski. The viscosity of UO_2.003 at the melting point measured by Palinski² is 4.6 cP (4.6 mPa s) which is within 7% of the value (4.3 cP) obtained with Eq. (1), given by Woodley. Thus, the equation based on the Woodley data is preferred. This equation has also been recommended in the assessment by Harding, Martin, and Potter.⁴

Figure 2

The viscosity of UO₂ was also measured by Nelson et al.⁵ at 3028 K and at 3068 K, which they believed was just above the melting point. Their viscosity values at these temperatures are 46 cP and 36 cP, respectively, which are about a factor of 10 above the viscosity at 3120 K calculated with Eq.(1). The temperatures and viscosities obtained by Nelson et al.⁴ suggest that these measurements were made below the melting point of UO₂. Thus, these data have not been included in this analysis.

1. R. E. Woodley, The Viscosity of Molten Uranium Dioxide, J. Nucl. Mater. 50, 103-106 (1974).



2. R. Palinski, Core Melts - Measurement of Some Thermophysical Properties of Liquid Reactor Materials at High Temperatures, Commission of European Communities Joint Research Centre, Ispra Establishment, Italy Report EUR 7002 EN (1980).



3. H. C. Tsai and D. R. Olander, The Viscosity of Molten Uranium Dioxide, J. Nucl. Mater. 44, 83-86 (1972).



4. J. H. Harding, D. G. Martin, and P. E. Potter, Thermophysical and Thermochemical Properties of Fast Reactor Materials, Commission of the European Communities Report EUR 12402 EN (1989).



5. R. P. Nelson, J. J. Rasmussen, and O. D. Slagle, Properties of Molten Fast-Reactor Oxide Fuels, pp. 2-4 to 2.26 of Battelle-Northwest Laboratory Report BNWL-1279 (February 1970); this study is also briefly described by J. L. Bates, C. E. McNeilly and J. J. Rasmussen, Materials Research 5, 11 (1971).