The temperature and pressure dependence of density allows directly the construction of a thermal EOS. At normal atmospheric pressure, the density was measured better than other properties for all three liquid metal coolants of interest. For Na and Pb, the experimental data are available from normal melting point up to normal boiling point7-11,22-26 and even up to higher temperatures59; for Pb-Bi(e), the upper temperature limit is about 1300 K,24 that is more than 600 K below its normal boiling point.

At normal atmospheric pressure (p0), the tem­perature dependence of the density (p) of most of normal LM can be described with an uncertainty of 1-3% by a linear correlation:

p(T;p0) = pM,0 — ap,0(T — Tma) [4]

where pM;0 is the density at normal melting temper­ature and Ap,0 is a constant.

The isobaric volumetric coefficient of thermal expansion (CTE) is, by definition, expressed through the density as follows:

_J @P(T, p) p(T, p) дт

Substitution of p in eqn [5] by correlation [4] yields for CTE at normal atmospheric pressure:

a (T, p0)

p,0

Sometimes, more complicated correlations are used to estimate a liquid metal density on the saturation line at high temperatures in the region close to the

critical point.22,59

Recent reviews of literature data on the thermo­physical properties of liquid Na,22 Pb, and Pb-

Bi(e)24,26,34 show that the uncertainty of correlation

[4] at normal atmospheric pressure is about 0.3-3% for Na and 0.7-0.8% for Pb and Pb-Bi(e) in the aforementioned temperature ranges. The recom­mended coefficients34 of the correlations [4] and [6] are given in Table 7, and the density and the isobaric
volumetric CTE of Na, Pb, and Pb-Bi(e) are presented as a function of temperature in Figures 4 and 5, respectively.

Densities of the liquid metal coolants of interest monotonically decrease with temperature due to the increase of the interatomic distances caused by ther­mal expansion; the CTE increases with temperature due to reduction of the interatomic forces with the distance.