Critical dimensions of systems containing /sup 235/U, /sup 239/Pu, and /sup 233/U: 1986 Revision Page: 8 of 205
This report is part of the collection entitled: Office of Scientific & Technical Information Technical Reports and was provided to Digital Library by the UNT Libraries Government Documents Department.
The following text was automatically extracted from the image on this page using optical character recognition software:
HISTORY OF EARLY CRITICAL EXPERIMENTS
EXPERIMENTS RELATED TO THE WEAPONS PROGRAM
The first Crit ical assembly wit h enriched uraijiulim* was ihe Los Alamos wat er boiler LOPO,
operate ed init ially in 1944. " This was a predecessor of HYPO that operated as a neutron
source for niany years. Of course, they were hot h preceded by reactor-oriented assemblies
of natural uranium, namely the Chicago and Oak Ridge piles.'9 LOPO was a 14.95-liter
sphere of 11(14.67)O2SO;H2O** solution at Hi /23U=647 in a 0.08-cm-thick container
and reflected by a roughly 90-cni-diain stack of beryllium oxide (density 2.7 g/cm3) on a
A bout the samie ti e, before U( -.90) became available, Los Alamos critical experiments
were directed toward weapon design. The critical assemblies of which descriptions have
been declassified consisted of U(-80) metal cores reflected by natural uranium, tungsten
carbide, or beryllium oxide; U(-74)HoC4 cores reflected by natural uranium, tungsten
carbide, beryllium oxide, or iron; and plutonium metal reflected by thin natural ura-
nium within tungsten carbide.20 The UH1oC4 was an intimate mixture of UH3 and Styrex
(('l,75-). Table 1 gives critical specifications of those assemblies with nearly regular ge-
onietries. Because uncertain geometric details cannot be clarified at this late date, these
specificat ions are given for historical interest rather than scientific value.
EXPERIMENTS RELATED TO THE GASEOUS DIFFUSION PROCESS
lIn 1945, Oak Ridge undertook the first of a series of critical experiments directed to-
ward criticality control of enriched uranium as UF6, the working material of the gaseous
diffusion plant .' Critical assemblies at that time came as close as practicable to sim-
ulating condensed U(24)Fc. with hydrogen moderation. One-inch cubes of an intimate
mixture of U(24)308 and as much viscous fluorocarbon, reported to be CFo.es, as would
retain its shape were prepared in 0.013-cm-thick aluminum. The effective composition,
t7(24)083C'5.3oF3.oA104, did not approach the actual F/U atomic ratio 6. Because the
available inventory, 9.5 kg 235U was subcritical without moderation, one-inch cubes of
polyethylene (('H, ,") were latticed among the uranium units to make some assemblies
critical. Table 2 gives the reported description of thest assemblies, with roughly cubical
cores reflected by paraffin. Because of a question concerning the reported fluorocarbon
forumuia.,*** t hese assemblihs, also, are described primarily for hist orical interest.
* l ranimu enriched in tle isotope 3" .
** Numbers in parent heses indicate the 23,51 content of the uranium in weight percent.
*** An expert in f[urcarbon clieumistry believe- that t he formula CF0.68 should represent a
s lid inst ead of a viscous fluid. The formula was provided by the laboratory oft he Gaseous
Diffusion Plant which produced ihe fluorocarbon.
Here’s what’s next.
This report can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Report.
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/m1/8/: accessed March 26, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.