The density of liquid uranium was measured by Grosse et a/.,80 Rohr and Wittenberg, 1 and Shpil’rain et a/.82 The results of the latter two studies are in very good agreement but deviate significantly from the results of Grosse et a/., which has been explained by errors caused by surface tension forces in the hydro­static weighing method used in that work.83 We have therefore selected the combined results from Rohr and Wittenberg81 and Shpil’rain et a/.,82 as recom­mended by the latter authors:

p(kgm-3)= 20332 — 2.146T (K) [4]

The density of liquid plutonium was measured by Olsen et a/.84 and Serpan and Wittenberg.85 The results are very close and the average of the two equations is recommended:

p(kgm-3) = 18004 — 1.486T(K) [5]

2.01.4.3 Viscosity

The viscosity of liquid uranium and plutonium has been measured using a direct oscillating method by researchers at the Mound Laboratory in the 1960s. These data are still the only available to date. For liquid uranium, Ofte86 reported:

log10Z(cP) = 1587.7/T (K-1) — 0.3243 [6]

The viscosity of liquid plutonium was reported in several studies, and the following equation is the recommended representation of the results87:

log10Z(cP) = 672/T (K) + 0.037 [7]

These equations give for the viscosity at the melting point 6.5 cP for uranium and 6.0 cP for plutonium. These values are somewhat higher than the values predicted by Grosse,88 who used an empirical rela­tionship between the activation energy for viscosity for liquid metals and their melting points, to obtain 5.9 cP for U, 4.5 cP for Pu, and 5.0 cP for Th at the melting point.

2.01.4.4 Surface Tension

The surface tension of liquid uranium was measured by Cahill and Kirshenbaum89 from 1406 to 1850 K. The results can be represented by the equation:

a(Nm-1) = 1.747 — 0.1410-3T (K) [8]

This equation yields 1.55 Nm-1 at the melting point. The surface tension of plutonium was reported by Olsen et a/.84 These authors obtained o(N m-1) = 1.29-0.967x 10-3 T(K), yielding 0.40Nm-1 at the melting point. It has been suggested that this value is too low because of dissolved tantalum. Spriet49 reported the surface tension of liquid plutonium to be 0.55 N m-1, which is generally accepted.