Critical dimensions of systems containing /sup 235/U, /sup 239/Pu, and /sup 233/U: 1986 Revision Page: 53 of 205
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WATER-SPACED UNITS OF ENRICHED URANIUM
Highly Enriched Uranium
unlike slightly enriched uranimn lat ices, wat er litIices of uranium enriched to more than
10% 23"1 have critical masses that are greater than the corresponding homogeneous sys-
tems. This is illustrated by results in Fig. 21 of Los Alamos measurements on lattices of
U(93.5) met al as 2.54-cm cubes, 1.27-cmn cubes and 0.31 8-(cmi-diaii rods.S2 Surface spacing
for minima in critical mass varies from 1.8 cm for the 2.54-cm cubes to 1.5 cm for the
A limited number of Oak Ridge experiments wit I MTH-type fuel elements provide guidance
for pool storage and recovery operat ions.13,14 These clement s were roughly 7.6-cm-square
in cross section and the fissile material, Ui(-93), was contained in a number of closely
spaced clad plates with the active fuel length about 60 cm. The 235U content was 140,
168 or 306 g per element. Measurements established, for each "raf loading, the element
separation in water required for optimum moderation and effects of greater separation on
the critical number of elements.
As an example, 47 of the 306 g elements spaced about 4 cm apart were critical latticed in
water. Further. 4 g 2351,/L as U(93)02t NO)2 dissolved in the reflector-moderator reduced
the critical mass of a compact lat tice by about one-third, and 1.12 g B/L dissolved in that
solution increased the critical mass by a factor of five. Influences of cadmium int erspersed
in various flooded storage patterns also were established.
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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/m1/53/: accessed March 19, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.