Capsule storage and density-analog techniques Page: 3 of 14
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CAPSULE STORAGE AND DENSITY-ANALOG TECHNIQUES
by
H. C., Paxton
ABSTRACT
Dansity-analgrg schemes for describing critical
arrays of fissile units have a long history. They
originated as methods for generalizin, results of
subcritical measurements on weapon capsules. Such
measurements were needed to establis, reasonably
efficient rules for capsule storage. Although spe-
cific density-analog models have been improved
throughout the years, they are now largely replaced
by comprehensive tabulations of critical-lattice
parameters. Certain simplified forms are still use-
fulias convenient formulas for extrapolation or for
gross sorting vv"safety features.INTRODUCTION.
In the 1940's the need to store mas-
sive weapon capsules led to density-analog
schemes for representing arrays of fissile
units. To. keep the scale of storage facil-
ities under control, it was necessary to
generalize the results of subcritical "vault
tests" that were undertaken at the Los
Alanos .cientifie Laboratory (LASL) in
1947.1 Recent declassification of infor-
mation about these tests and about subse-
quent measurements involving weapon compo-
nents allows us to review the history of
density-analog techniques. I. aidition to
explaining the origin and applications of
these techniques, we point out the extent
to which they have been disrtlaced by pre-
rise representations of critical arrays,
and suriest ways in which they can still te
useful.
.sc'r Wunl WFAPu2OFNx
Vazeuit 2c. a. The name "vault test" was
.lrlvod from lIe arrangueent 61h1 wa in Fi;.
). A lI Irtweight frimew-rk prtvldtu luca-'Itions for as many as 27 capsules in a cubic
array, which could be surrounded completely
'by concrete. The framework was in two parts
and was mounted cn tracks so-that the two
portions, with part of the concrete, could
be withdrawn in opposite directions. A
scram signal automatically actuated the
withdrawal, and it was possible to reassem-
ble remotely. Concrete wails and roof were
1 ft thick and the floor was of 6-in.-thick
reinforced concrete. The interior dimen-
sion of the cubic vault could be adjusted
to 3, 4, nr 5 ft. Spacings provided by the
framework could be adjusted to correspond.
Basic components, called "fissile
units," were U(9;)-Pu combinations, each
equivalent in reactivity to a sphere of
about 20 kg U(93). An entire capsule, call-
ed a "tamped un'.t," was a fissile unit sur-
rounded by natural uraIum varying in thick-
ness from h to 2k in. ieutron-multiplica-
tion values were measured as adjacent lir.-
tice positions were filled progressively
by fissile units, then by tamped units, and
finally by missile units opened into halves.
,i' 1
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Paxton, H. C. Capsule storage and density-analog techniques, report, May 1, 1975; New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc880178/m1/3/: accessed April 18, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.