United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 93-05: Locking of Radiography Exposure Devices

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
              OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS
                           WASHINGTON, D.C.  20555

                              January 14, 1993


Information Notice No. 93-05:  LOCKING OF RADIOGRAPHY EXPOSURE 
                                   DEVICES


Addressees:

All Nuclear Regulatory Commission industrial radiography licensees 

Purpose

This information notice is intended to:  (a) alert licensees that the locking
mechanisms on certain industrial radiography exposure devices can be locked
with the sealed source in the exposed position; and (b) emphasize the
importance of ensuring that the source is secure in a shielded position before
moving the device.  We expect that licensees will review this notice,
distribute it to responsible staff, and consider actions, if appropriate, to
verify that the source is properly secured at the conclusion of radiographic
operations.  However, suggestions contained in this notice do not constitute
any new NRC requirements, and no written response is required.

Description of Circumstances

Case 1:  A radiographer was overexposed in an incident involving a
disconnected source when he failed to conduct a survey after each exposure. 
After investigating the incident, it was discovered that the radiographer had
approached the device without a survey instrument, locked the device,
disassembled the source guide tube, and left the drive controls connected
before moving the device from one location to another.  The radiographer had
incorrectly assumed that in locking the exposure device, he had secured the
source in a shielded position.  In fact, the sealed source remained in the
guide tube because the pigtail had disconnected from the drive cable.  The
radiographer's error was further compounded when the drive cable was not
removed before moving the device, which would have allowed him to identify the
absence of the source pigtail within the shielded assembly.  

Case 2:  A radiographer was performing radiographic exposures of welds on a
series of pipelines that were located approximately 6.1 meters (20 feet) above
ground.  The radiographer used a 1.8-meter (6-foot) guide tube with collimator
and a 7.6-meter (25-foot) control cable.  The radiographer hung the device
from the pipeline to perform the work with the control cables hanging down to
the ground.  After an exposure, the radiographer retracted the source, placed
the control cables on the ground, and used a hydraulic lift to get to the
camera.




9301080120.

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Because the camera was suspended above the lift, the radiographer had to move
the camera to reach the locking mechanism.  He moved the camera by grasping
the control cables with his right hand and locking the camera with his left 
hand.  He continued with his left hand to disconnect the guide tube from the
camera.  At this point, he noticed that the sealed source was protruding
approximately 10 centimeters (4 inches) from the camera port.  (Note:  His
alarming ratemeter did not sound because it was not turned on.  This violation
of 10 CFR 34.33, which can result in a civil penalty, is addressed in
Information Notice 91-49:  "Enforcement of Safety Requirements for
Radiographers").

Reenactments of the incident showed that when the radiographer turned the
device, the crank handle could drag on the ground, exposing the sealed source. 
The radiographer was then able to lock the device over the drive cable, with
the sealed source protruding approximately 10 centimeters (4 inches). 
Analysis of the locking mechanism after the event did not identify any obvious
defects with the mechanism.  Tests performed showed that the device could
still be locked with the source in the exposed position.

NRC Evaluation:

The findings in both of these cases raised concern among NRC staff that, under
certain conditions, radiographers could have false confidence in the locking
mechanisms.  If exposure devices can lock when the source is outside of the
shielded position, then radiographers could incorrectly believe that they are
protected from exposure when, in fact, the source is not in its fully shielded
position.  We are also concerned that exposure devices are moved while the
drive cables are still connected.

To evaluate the effectiveness of the locking mechanism on radiography exposure
devices and to determine whether radiographers commonly move the devices with
drive cables still connected, NRC inspectors observed licensee equipment tests
and interviewed radiography personnel.  From the data collected, we determined
that a majority of exposure devices can be locked when the source is in a
variety of positions, rather than only when the source pigtail is properly
seated, with the source in the fully shielded position.  Many source pigtails
include a "locking ball," designed to prevent the source from moving forward
when the lock is engaged; however, our observations show that some exposure
devices may be locked both when the source is not fully retracted and while
the drive cable is seated under the locking pin, thereby circumventing the
locking-ball feature.  This may result in a source being positioned where it
is not fully shielded.

Many radiographers acknowledged to NRC inspectors that they often leave drive
cables connected when moving an exposure device from one location to another
at temporary job sites.  In addition, some acknowledged leaving the guide tube
connected.  One licensee stated that this practice had resulted in a source
being forced out of the exposure device while the device was carried to a new
location at a temporary job site.  This licensee noted that the device was
locked at the time, but the source had not been fully retracted before locking
the device..

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Discussion:

All licensees are reminded of the importance of ensuring that the sources used
in radiography exposure devices are properly secured and fully shielded before
moving the device.  Radiographic exposure devices manufactured and new
equipment acquired by licensees after January 10, 1992, must meet new design
requirements in 10 CFR 34.20.  These require that, among other safety
features, the device must automatically secure the source assembly when it is
cranked back into the fully shielded position within the device.  However,
many radiographic exposure devices currently in use do not include the newer
safety features, and licensees are not required to use devices that comply
with 10 CFR 34.20 requirements until after January 10, 1996.  Certain
radiography exposure devices still in use today may be able to be locked with
the source in the exposed position.

Experience has shown that when an older exposure device is in use, the locking
mechanism is not an indicator that the source is fully retracted and secured. 
The use of engineered safety features, like the lock mechanism, MUST BE
coupled with a proper survey (10 CFR 34.43) AND use of an alarm ratemeter 
(10 CFR 34.33), to prevent the unintentional exposure of personnel.  Surveys
must be sufficient to detect a change in exposure readings taken at the source
tube outlet, to determine whether the source is fully retracted to a shielded
position (10 CFR 34.43).  Alarm ratemeters serve as an additional warning
method.  Additionally, it is recommended that radiographers disassemble the
source guide tube, remove the drive controls, and install the safety plugs or
covers, before moving the radiography exposure device to another location. 
The failure to do so has been identified as a contributing factor in the
unintended exposure of personnel, as well as in incidents where radiographers
failed to notice that the source was not retracted into the device.

Sealed sources for radiography are capable of delivering significant exposures
to radiography personnel and to members of the general public, when handled by
individuals who are inattentive to radiation safety procedures.  It is
recommended that all workers understand the consequences of improperly
handling radiographic devices, and that workers be encouraged to use necessary
precautions when working with these devices.
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No written response is required by this information notice.  If you have any
questions about this matter, please contact the appropriate NRC regional
office or the personnel listed below.


                                       ORIGINAL SIGNED BY


                                    Richard E. Cunningham, Director
                                    Division Industrial and
                                      Medical Nuclear Safety, NMSS

Technical contacts:  Gary Shear, Region III
                     (708) 790-5620

                     Charles Cain, Region IV
                     (817) 860-8186

                     Scott Moore, NMSS
                     (301) 504-2514

Attachments:
1.  List of Recently Issued NMSS Information Notices
2.  List of Recently Issued NRC Information Notices

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Page Last Reviewed/Updated Tuesday, November 12, 2013