Measurements of UF$sub 6$ cylinders with portable instruments Page: 2 of 39
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Means for inexpensive, rapid, nondestructive verification of
UF6 cylinder content has been a subject of considerable interest and much
speculation. The international market for enriched uranium fuel and in-
terests in enrichment processes further emphasize the need for simple
verification techniques for safeguards and materials control.
A limited test of the gamma enrichment meter method for
determining the enrichment of UF6 in shipping containers was conducted
two years ago at the Goodyear Atomic Enrichment facility (GAT), Piketon,
Ohio. 2 Measurements on five 5A and two 48A cylinders, performed with a
portable Nal instrument, indicated that accuracies of < 10% might be possi-
ble. Variation in container wall thickness was noted as a source of appre-
ciable error for the gamma method. 3 Encouraging results for cylinder
assay by the gamma method were also obtained by A. R. Flynn, Oak Ridge
Gaseous Diffusion Plant (K-25), Oak Ridge, Tenn. 4 Another passive tech-
nique proposed for verification of UF6 cylinders is the detection of neutrons
emitted from 19F(, n) reactions and the spontaneous fission of 238U. 3, 5
This technique for UF6 assay is used routinely at GAT for detection of
holdup in the enrichment cascade. 6
Recently, as a part of a study of perimeter safeguards for
enrichment facilities, LASL Group A-2 has measured passive neutrons and
gamma rays emitted from cylinders of UF6 representative of a wide range
of enrichment and container sizes.7 Additionally for these studies, an
active neutron interrogation system, devised by Caldwell, 8 was success-
The purpose of the present work was to better define the
accuracies and limitations of these techniques by testing them on a large
number of UF6 cylinders, primarily of type 30 (22 ton), the standard ship-
ping container for power reactor feed material. All measurements were
performed with portable instrumentation in the field and with minimal
intrusion on normal plant operation. Most of the data were collected in a
total of seven days at K-25 and GAT.
IL PASSIVE NEUTRON ASSAY
A. Neutron Yield of UFS
234U is the dominant a emitter in enriched uranium and hence
the principal source of neutrons from 19F(a, n) neutrons in UF6. If the
ratio of 235U/234U is known, passive neutron counting can be used for
235U assay. This ratio may vary by as much as a factor of two over the
complete range of enrichment, but for low enriched uranium (< 5%), it is
more nearly constant and verification measurements of limited accuracy
may be possible without specific 234U isotopic data.
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Walton, R.B.; Reilly, T.D.; Parker, J.L.; Menzel, J.H.; Marshall, E.D. & Fields, L.W. Measurements of UF$sub 6$ cylinders with portable instruments, report, January 1, 1972; United States. (digital.library.unt.edu/ark:/67531/metadc1032400/m1/2/: accessed November 14, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.