Critical dimensions of systems containing /sup 235/U, /sup 239/Pu, and /sup 233/U: 1986 Revision Page: 10 of 205
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TABLE 2. CRITICAL CUBIC LATTICES OF 1-IN. CUBES OF
Uj24)O2 5(). F53o 3.cxoA 104 (DENSITY 3.50 g/cm13) AND CHsr
(DFNSITY 0.915 gcimi) REFLECTED BY t6-IN.-THICK PARAFFIN.
H / '3 Average Critical Mass
H Cubes 'T Cubes Atomic Ratio Deusity(g/cnm3) (kg 2351J)
3/4 46 2. 14 8.3
1/1 63 .95 6.1
2/t 129 1.67 3.9
In 1946 there was s1hieut highly enriched uranihuIII to extend the above experiments with
one-inch cubes of initimnately mixed U l" and polytetraflhoroethylene (CF2)", effectivey
UF6C. These were latticed with either one-inch-cubes or 1 x 1 x 0.5 in. half-cubes of
polyethylene. A series of experiments witn U(95.3) was conducted by Oak Ridge person-
nel at Los Alamos.22 Roughly cubic cores with 18-cm-thick paraffin reflectors consisted
of hydrogen-to-uranium cubes in the ratios 11:1, 1:1. 2:1, 4:1, and 7:1. For the 1:1 ratio,
heterogeneity was varied such that there was reasonable extrapolation to a homogeneous
cre, with t he result included later in Table 10. Critical masses for all hydrogen-to-uranium
cumbhinat ions, uncorrected for heterogeneity, appear in Fig. 1 as the left-most curve. Ap-
proximate densities of 2350 in g/cm3 may be obtained by dividing 14.8 by H/235U.
Later that year, a similar series of experiments was performed at Oak Ridge with U(29.8)
instead of highly enriched uranium."3 Again, one composition could be corrected reason-
ably for heterogeneity, with the result included in Table 10. Uncorrected critical masses
also appear il Fig. 1. The curves rise at large H/!35 U as a result of extreme heterogeneity.
The expression relating 235U density and H/235U given above for U(95.3) also applies for
Although not belonging to this very early period, the only known experiments with ho-
mogeneous hydrogen-mlloderat.ed 'FF are described here to complete the account of UF6
crit icality In this series of experiments, performed at Valduc, France. * the primary ma-
terial was liquid U 93)Fc to which various proportions of liquid HF were added while
retaining homoge(.1ity. These mixtures were contained in 0.4-cum-thick Monel spheres sur-
rounded by an elFfectivel: infinite thickness of water.
Experimental critical data appear in Table 3 and in Table 4 after adjustment to spherical
vollies and normialization to 75"C. Figures 2 and 3 show critical vollhines, diameters, and
llasses as fluce lolls of -1/25U at omic ratio and 2"5U density. The available inventory of
UF ;, 93.9 kg 23'1-, coulld not he made critical without internal hydrogen. Consequently,
ihe entry under I '"1' - 0 in Table 4 is the result of ext rapolat ions shown in Figs. 2 and
3, sipp irted by lMonte Carlo and transport calculations.
* La St at iou le Crit icalite d' Valdc may he called simply Valdlc. or Dijon. which is nearby.
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Paxton, H.C. & Pruvost, N.L. Critical dimensions of systems containing /sup 235/U, /sup 239/Pu, and /sup 233/U: 1986 Revision, report, July 1, 1987; New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc1109879/m1/10/: accessed March 19, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.