Description of occurrence (edited from investigation report) cont'd

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