Critical dimensions of systems containing /sup 235/U, /sup 239/Pu, and /sup 233/U: 1986 Revision Page: 16 of 205

As Fig. 2 indicates, the minimum critical volume occurs at H/U about 30. Further, UF6-
HF mixtures at any concentration cannot be made critical in wat er-reflected spheres 45-cm
or less in diameter provided the temperature is at least 75"C.
TRANSITION TO FACILITIES FOR CRITICAL EXPERIMENTS
Returning to the very early experiments, it may be noted that they vere conducted in
improvised facilities. Two Los Alamos fatalities2- underlined the need for improved pro-
tection of personnel, and permanent facilities designed specifically for the safe performance
of critical experiments were in operation at Los Alamos in 1947 and at Oak Ridge in 1950
after experiments starting in 1946 at an interim facility. There followed at Oak Ridge
extensive programs with uranium enriched in 235U and 233U, which contribute to the re-
mainder of this report.
In 1951, critical experiments with plutoiunm solutions began in a Hanford facility that was
temporary but had adequate permuel protection.21 TIe permanent. plutonium critical-
mass facility at Hanford became operable in 1961.27 These facilities provided much of the
data for moderated plutonium systems that are included in this report.
Other laboratories that have provided results of critical experiments are at Aldermaston,
England, operation beginning in 1952; 8 Livermore (from 1955 in its appropriate facility);9
Dounreav, Scotland (from 1957); 9 Saclay, France (from 1960);30 Valduc, France (from
1963);30 and Rocky Flats (from 1965).3 We have no information on USSR facilities at
which criticality data have been generated.

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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/m1/16/ocr/: accessed April 18, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.

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