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Summary - Density of Solid Uranium Dioxide

Recommended Equations

The recommended equations for the density of solid uranium dioxide are based on the lattice parameter value of 0.54704 nm obtained by Gronvold [1] at 293 K and the 1988 assessment of thermal expansion by D. G. Martin [2]. They are in agreement with the 1989 recommendations of Harding, Martin, and Potter [3]. The lattice parameter of Gronvold is in good agreement with recent measurements by Hutchings [4]. Assuming the molecular weight of UO₂ is 270.0277, this lattic parameter gives a UO₂ density at 293 K of 10.956 Mg/m^-3. Applying the thermal expansion recommendation of Martin, the density at 273 K is 10.963 Mg/m^-3.

The density as a function of temperature may be calculated from:

where rho(273) is the density at 273 K; L(273) and L(T) are the lengths at 273 K and at temperature T(K), respectively. The ratio of the length at 273 K to the length at temperature T(K) may be calculated from Martin's equations for the thermal expansion of solid UO₂:

ERROR: The last factor in the previous equation should be 4.391E-13. Thanks to Jamie Higgs of the Dept. of Chemistry and Chemical Engineering at the Royal Military College of Canada for pointing this out.

The densities as a function of temperature of solid UO₂ are given in Table 1.

From assessment of the available data on hyperstoichiometric uranium dioxide (UO_2+x), Martin recommends using the same equations for the linear thermal expansion of UO₂ and of UO_2+x for x in the ranges 0 to 0.13 and 0.23 to 0.25. Therefore, equations (1) through (3) are recommended for the density of UO_2+x for x in the ranges 0 to 0.13 and 0.23 to 0.25.

No data on the effect of burn-up on density or thermal expansion of UO₂ are currently available. In the absence of data, equations (1) through (3) are recommended for UO₂ during irradiation, in accord with the recommendation of Harding, Martin, and Potter [3].

Figure 1

The recommended uncertainty in the density of UO₂ is 1% for the entire temperature range. The uncertainties in the density of UO₂ calculated from the thermal expansion uncertainties given by Martin [2] are less than 1%. The 1% uncertainty is based on comparison of the recommended density with those of previous recommendations based on different data. Figure 1 shows the recommended density, the 1% uncertainty, and the 1981 recommended values [5] that are based on the thermal expansion values of Olsen [6] and a density at 298.15 K of 10.97 Mg/m^-3.

1. F. Gronvold, J. Inorganic and Nucl. Chem. 1 357, (1955).

2. D. G. Martin, The Thermal Expansion of solid UO₂ and (U,Pu) Mixed Oxides - A Review and Recommendations, J. Nucl. Mater. 152, 94-101 (1988).

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

4. M. T. Hutchings, High-Temperature Studies of UO₂ and ThO₂ using Neutron Scattering Techniques, J. Chem. Soc. Faraday Trans. II 83, 1083-1103 (1987).

5. J. K. Fink, M. G. Chasanov, and L. Leibowitz, Thermophysical Properties of Uranium Dioxide, J. Nucl. Mater. 102 17-25 (1981).

6. C. S. Olsen, Fuel Thermal Expansion (FTHEXP) in MATPRO- Version 11: A Handbook of Materials Properties for Use in the Analysis of Light Water Reactor Fuel Rod Behavior, ed. D. R. Hagraman and G. A. Reymann, US Nuclear Regulatory Commission Rep. NUREG/CR-0497 (February 1979); also revision (1981).