Critical dimensions of systems containing /sup 235/U, /sup 239/Pu, and /sup 233/U: 1986 Revision Page: 88 of 205

A dd ional iiiforimaticw about lioiIogeieously distributed poison is yielded by PCTR ex-
periienl . s, lamely, the cucentat ioll required ii a fissile mixt ure to reduce k, to unity.
Figure -10 gives results for tlhe efFect of 1 ro in hioiiogeneous 1'(3.01)03-polyet lyleiie mlix-
Ilures at varilts 11 -"i''. at 111iC rat ios"' alld also iicluides a point for a U(2.00)F,4-paralli
imixtur."1 Figure 41 gives the fborou c1centratiou required to reduce k, to unity for
optimally Moderated homlogeiieous rmixtures of hydrogen and uraiiiumi as a function of the
uranium eiirichlmueiit . The values at 3.04 and 1.03 wti, were established experimentally;"'8
the value at 2.00 wt i, was estimated fronm the ol' 1imeas1Irelieit shown in Fig. 40. The
ext rapolat ion beyn d 3 *.t t is t ent at iv e. "
Plutonium Solutions
llaiihrd data oil the influence of excess iiitrate on the critical mass of water-reflected
plutonium solut iols2 was shown ili Fig. 2S. There is less extensive information from the
same source oil poisoliiig by lithium, bisunth, alndl phosphate.
Effects of gadoliuimuui as an absorber in plutoimiu-iitrate solutions were measured at
Hanford in a GI-cim-diaui cylinder reflected with water on the lateral surface and base. ""
For a solution containing 116 g Pu /L, 8.3% 240Pu, and 1.85 N HNO3, crit ical heights ranged
front about 17 cm to +G cii as gadolinium was added progressively to a concentration of
about 2.4 g /L. According to calculations based on the experimental results, 4 g Gd/L would
reduce k, to unity. Similar measurements with solution at 363 g Pu/L, 8.3% 240Pu, and
4.1 N HNO3 extended the absorber concentration to 20 g Gd/L. In this case the deduced
gadoliuiiii concentration for k.- = 1 is about 70 g/L.
Crit ical radii of wat er-reflected spheres of' P4(4.7% 240Pu)-T solution containing gadolin-
ium were also est ablished at llauford." Results are summarized in Table 23.
Other Hanford experiments with absorbers included effects of randomly packed glass or
stainless steel Raschig rings ill plutonium-nitrate solution, 121 and comparisons of plates of
various absorbers extending through Plexiglas-reflected PuO2-UO2-polystyrene
assemblies.2'm23 l the first case, glass Raschig rings, 3.8-cm-dian by 4.3-cm long and
0.32-cm wall thickness, contained either 0.5 or 4 wt% boron, and stainless-steel rings,
1.27-cm-diam by 1.27-cm long and 0.16-cm wall thickness, contained I wt% boron.

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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/m1/88/ocr/: accessed April 22, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.

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