Investigation of breached depleted UF sub 6 cylinders Page: 3 of 12
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pressure. analyzing gas and salt
samples, emptying one cylinder, and
sampling internal reaction products
from the other cylinder. Details of
the procedures followed in these
examinations and related problems
are described in a companion paper
presented at this Conference (1).
Another companion paper (2) presents
the chemical findings uncovered in
these examinations and their general
implications for continued cylinder
storage. The present paper
discusses the failure cause and the
associated lessons learned that can
be applied to improvements in
cylinder design and cylinder storage
practices. Members of the
investigation team who were
instrumental in the failure analysis
consisted of Energy Systems
personnel (Jack DeVan. Chairman,
John Barker, John Googin.
Tim Butler, and Mike Taylor) and
Department of Energy representatives
Bob Dyer and Joe Russell. An
interim final report covering their
investigation was issued in
September 1991 (3).
INVESTIGATION STRATEGY
The lesser damaged of the two
cylinders was investigated first,
since it was hoped that the initial
cause of failure would be less
obscured by subsequent exposure of
the cylinder contents to the ambient
atmosphere. To access this
cylinder, over 200 stacked cylinders
had to be moved with the Raygo
Wagner loader. Several nearby
cylinders were observed to be
dented at, or near, the location
where both failures had occurred.
These other cylinders were examined
for cracks; however, none was found.
Once access had been gained, the
cylinder was pressure checked and a
gas sample taken for chemical
analysis. As would be the case for
an undamaged cylinder, the internal
pressure was still less than
atmospheric (-4 psig at 85 F), andthe gas analysis showed negligible
oxygen or nitrogen contamination.
The cylinder was then patched.
removed from the storage yard. and
valved at ambient temperature into
the cascade. After removal of the
UF6, the breached area was X-rayed
and the internal cylinder surface in
the area of the hole was imaged in
the X-705 annex using a miniature
video camera mounted on a flexible
cable. Presently, this cylinder is
in storage awaiting sufficient
radioactive decay to allow removal
and evaluation of the material still
plugging the hole and metallographic
examination of the cylinder wall.
To clear a path to the cylinder with
the larger hole. 60 neighboring
cylinders had to be moved. The
pressure in this cylinder was above
atmospheric (+8 psig at 85 F) and
contained elevated concentrations of
HF. The hole was covered by an
aluminum patch, and core samples of
the salt underlying the hole were
taken through two ports in the patch
for chemical analyses. The cylinder
was weighed for accountability and
then valved into the cascade.
Evacuation was begun in the same
manner as for the cylinder with the
smaller hole and was continuing at
the time of this report.
DESCRIPTION OF FAILURES
The larger of the holes found in the
two breached cylinders at Portsmouth
is pictured in Fig. 1. The area of
salt exposed by the breach was
approximately 9 in. along the axis
of the cylinder and 13 in. from top
to bottom. Viewed from the valve
end, the hole was centered at the
9 o'clock position and extended
under the nearest stiffening ring.
The upper corner of the lifting lug
of the adjacent cylinder was
positioned at the approximate center
of the hole. A green-colored,
jagged. fluoride salt layer covered
the exposed hole area slightly below
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DeVan, J. H. Investigation of breached depleted UF sub 6 cylinders, article, January 1, 1991; Tennessee. (https://digital.library.unt.edu/ark:/67531/metadc1058239/m1/3/: accessed June 8, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.