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Radiological Assessor Training
DOE-HDBK-1141-2001
Student's Guide
There are levels of 234Th and 234mPa that occur
naturally from the decay of 238U present in the
cylinder pigtail, pigtail gaskets, and cylinder valves.
Approximately one curie each of those two
radioisotopes builds up in a cylinder within a few
months. These materials are less volatile than UF6,
so they remain as solids at the autoclave
temperature, but some small amounts are entrained
in the UF leaving the cylinder and small quantities
are deposited in the cylinder valve and pigtail as the
UF passes through it. These materials are present
as removable surface contamination in these
components, as well as being present in quantity in
the cylinder heels (the material remaining in the
cylinder after feeding). No containment of the ends
of the pigtail during the gasket removal process was
required by procedure. Additionally, the facility-
specific training program does not address the
specific contamination hazard the cylinder/pigtail
change represents.
The operators changed four cylinders on the shift.
The cylinder number, autoclave used, and
approximate time of change (from logs and recorder
data) are shown below:
Cylinder Number
Autoclave Number
Approximate Time
K-438
3 West
0130 08/23/91
K-505
5 West
0320 08/23/91
K-472
1 West
0500 08/23/91*
AC-1090
4 West
0500 08/23/91
*Time is very approximate. Operator statements place the change late in shift.
Module 16 - 5


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