Critical dimensions of systems containing /sup 235/U, /sup 239/Pu, and /sup 233/U: 1986 Revision Page: 91 of 205
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TABLE 23. CRITICALITY OF PLI'TONII'M - UlRANIUM SOLUTIONS
CONTAININC CADOIIN INI
Sphere \\all wt I'l I I N03 Critical Radius(cmj
Thickness(cmi in Pu - l' g Puf L i G1 . rmlity" Observed CaIc.,no Gd
0.112 31 70.9 11.051 3.12 17.S7 17.11
0.122 32 35.0 0.027 1.49 19.30 18.36
0.122 15 45.6 0.005 2.1 19.31 19.26
Plut oni u-nit rate solutions ranging from 63 to 412 g Pu L were crit ical in 30.5-, 45.7-, and
61-ct diam water-retlected tanks without Haschig rings but only in the 61-ci tank with
0.5 wt i berated rings. Exponential mueasuremients wit i t- -1 wt ' horated rings indicated
that bucklings were negative for all plutonium concentrations below 391 g/L. Similarly,
with 1 wt% borated st ainless steel rings, bucklings were negative for concentrations below
412 g Pu/L.
Two sets of measurements were reported for reflected PuO2-iO:2-polystyrene assemblies
at H '(Pu- U) = 30.6 with 14.6 wt% PuO. in the PuO2+.U02., and H/(Pu U) = 2.8 with
29.3 wt' PuO , in t he PuO ,4 L 2'1 The first composition was selected to give a
relatively soft neut ro-tlhx spectrum, and the second composition a hard spectrum. In
the first set eit her one or two plates of copper, topper plus 1% cadmium, or aluminum ex-
t. nded thro gh the core near its midplane. Critical conditions were described adequately
for comparison wit h \Monte Carlo calculations. in the second set of experiments a single
absorbing plate extended through assemblies of the same compositions. In order of ef-
fectiveness, the absorbers tested were oral. cadmium, stainless steel containing 1.6 wt %.
boron, stainless steel containing 1.1 vw'% boron, stainless steel without boron, uranium
depleted to 0.2 wt' 2171. and lead. Again. the critical assemblies were well described.
Uranium 233 Solutions
The effect of nitrogen as an absorber has been indicated by the comparison of critical
masses of 3 O"( NO, solutions with 233 U O solutions in Table 21. Further. the
influence of borosilicate glass Raschig rings in V3 solution is included in Table 24. The
only other eXPerimnents w ith poisoned 3:'U solutions, also at Oak Ridge, gave the effect
of boron on t he critical concentration of 2 33 in a 69-cm-diam sphere of 2331102(NO3)2
sohition with little excess nitrate." ii sunminiary. the addition of H3B03 in an amount
corresponding to 0.0)91 g B L required an increase of =331 concentration from 16.7 g/L
(H' 1, - 1530) to 19.4 g L (H 233i' = 1320) to maintain criticality. This represents
about 0.75 atoms of boron per atom of added 2331"'
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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/m1/91/: accessed March 21, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.