Critical dimensions of systems containing /sup 235/U, /sup 239/Pu, and /sup 233/U: 1986 Revision Page: 33 of 205
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Sources of experimental data and tihe nature of conversions to the conditions of Figs. 10 to
13 are as follows. The portions of those figures for the 1l/=35T range greater than 20 are
based on many critical-solution Ineasuremwnlts of a variety of cylinders,32'33 some spheres
or cubes,22'48-51 and a slab.31
The value of thickness of a critical infinite solution slab reported in Ref. 34 was obtained
by extrapolating the reciprocal critical height of vertical finite slabs to zero. Alternatively,
the infinite slab t hickness may be obtained from the least subcritical finite slab by means
of Table 5 and Fig. 6. The result at H/235U 44.7, 5.0 cmt (including Plexiglas correction
of 0.25 cni), compares with 4.5 cii reported in Ref. 34. There was a similar reexamination
of the critical infinite slab thickness reported for Plexiglas-reflected U(93) nietal.3' The
result, 1.38 cm, compares with the reported value of 1.52 cm) (0.6 in.).
The most nearly equilateral critical cvjlinders are generally ;elected for conversion to
spheres, elongated for infinite cylinders, and squat for infinite slabs. Conversions to the
required shape make use of' Fig. 6 and Table 5. Extrapolation of critical solutions con-
centration data to zero buckling gave 12.30 f 0.10g of 235U/L as the limiting critical
concentration,m and 12.05 0.03 resulted from measurements at the Hanford Physical
Constants Testing Reactor (PCTR).52
Although they do not apply directly to the curves, critical data for slightly moderated
solids are available for checking calculated points, for example, cores of effective compo-
sition U(93.15)12.9 C1,11O.25 were reflected by natural uranium or iron.45 More nearly
appropriate is the critical mia-s of paraffin-reflected U(95.3)F6C mixed with polyethy-
lene, of H/2"U 10 (Ref. 22). The enriched-uranium-metal points were based on Los
Alamos values20'53 4 and ORNL slab data" (with DSN correction from Plexiglas to wa-
ter reflector). supported by measurements at Lawrence Livermore National Laboratory
(LLNL).'6"'" Shape conversions for the metal made use of extrapolation distances from
Fig. 7. Core-density corrections for water-reflected spheres were made by using the com-
puted relations of Fig. 9 and, for metal, the experimental points of Fig. 8. In regions of
scanty or uncertain data, the curves of Figs. 10 to 13 are guided in form by results of DSN
Points of Fig. 10 for water-reflected U(93)O2-H20 (Table 8) mixtures are those reported
by Magnuson of Oak Ridge." They result from calculations validated by comparison with
dense crit ical arrays of 1O2 -C5O211 , units reflect ed by polyethylene and cont.aimiing internal
methyl met hacrylat e.
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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/m1/33/: accessed March 25, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.