Information Notice No. 81-37: Unnecessary Radiation Exposures to the Public and Workers During Events Involving Thickness and Level Measuring Devices

                                                           SSINS No.: 6835 
                                                           Accession No.: 
                                                           IN 81-37 

                               UNITED STATES 
                           WASHINGTON, D.C.  20555
                              December 15, 1981

                                   PUBLIC AND WORKERS DURING EVENTS 
                                   INVOLVING THICKNESS AND LEVEL MEASURING 


This information notice provides information about radiation hazards 
associated with the possession and use of measuring devices containing 
radioactive sources.  These devices are generally considered to present only
minimal potential for radiological problems under normal use conditions. 
However, two recent events involving measuring devices resulted or may have 
resulted in unnecessary radiation exposure to members of the public and to 
maintenance workers.  This information should be brought to the attention of
all persons involved in the administration and operation of facilities and 
processes using measuring devices.  Particular attention should be given to 
the environment where measuring devices are located and to procedures to 
assure that the radioactive source is properly c shielded and contained. 

Description of Circumstances: 

Case 1:   An NRC licensee was closing a facility in Oklahoma City, Oklahoma 
and had sold a trailer containing a mounted measuring device (Tube Wall 
caliper) for determining pipe wall thickness.  Since the device contained a 
1.5 curie cesium-137 source and the new owner had not yet obtained a license
to possess the radioactive source, the licensee removed the device from the 
trailer prior to the new owner taking possession.  During removal of the 
device (which was performed by an unauthorized user), the radioactive source
was inadvertently released from its shielded position in the device and fell
to the trailer floor.  The dismounting of the device was performed without 
benefit of a survey meter or personnel monitoring equipment.  The radiation 
dose to the individual may have been as high as 600 millirems.  
Subsequently, the new owner had the trailer towed to Houston, Texas, with an 
interim stop for tow truck engine repair in Norman, Oklahoma.  The driver, 
who was not aware of the presence of the radioactive source, waited near the 
trailer for approximately four hours.  He may have received a radiation dose 
as high as 1.4 rems.  The next day, the licensee found that the source was 
missing from the measuring device.  Local health authorities performed a 
search using radiation detection equipment along the highway route between 
Oklahoma City and Houston.  The source was found lodged on a bridge support 
structure near Lewisville, Texas. 

The major causes of the event were that (1) the licensee failed to employ an
authorized user to remove the device, and (2) the unauthorized user failed 
to make a radiation survey. 

                                                           IN 81-37 
                                                           December 15, 1981
                                                           Page 2 of 2 

Case 2:   A cooler in an iron ore pellet plant was shut down for repairs on 
March 30, 1981.  On that day, the shutter mechanism of a level control 
device, which contained a nominal 10-curie cesium-137 sealed source, was 
locked in the closed position.  Radiation surveys performed at that time 
indicated that the source appeared to be properly shielded.  After a 
cooldown period, workmen entered the cooler on April 3, 1981 to replace 
refractory material on the cooler walls.  On April 7, licensee personnel 
discovered that there were radiation levels in excess of 100 millirems per 
hour within the cooler (later determined to be as high as 2.2 rems per hour 
where the radiation beam entered the cooler).  It was determined that 
several individuals had been exposed to a radiation beam from the source 
during the working days between April 3 and 7, 1981.  The device source 
holder was removed from its mounting, and licensee personnel found that the 
lead shielding in the shutter had melted and drained from the shielded 
location. This rendered the shielding integrity of the shutter useless. 

Investigation showed that 17 licensee personnel and 14 contractor personnel 
had entered the cooler between April 3 and 7, 1981.  The calculated 
radiation exposures received ranged from 0.14 to 3 rems.  During the 
repairs, the pellet cooler area was considered an unrestricted area.  It is 
estimated that 14 of the 31 individuals exposed may have received whole-body 
exposures in excess of 0.5 rems.  No health effects were observed or would 
be expected from these exposures. 

The event occurred because a hole had been cut in the side of the cooler to 
reduce shielding and allow more effective operation of the cesium-137 source
in the device.  During recent efforts to increase production, the pressure 
of the air forced into the cooler had been increased as a means of 
accelerating the cooling of the pellets.  As a result, hot gases may have 
been forced out of the aperture in the cooler wall at the location of the 
source holder.  The temperature of the pellets entering the cooler is about 
2400F, considerably higher than the melting point of lead.  The heat 
reaching the device was sufficient to melt the aluminum alloy dust cover 
over the device shutter mechanism and the lead in the shutter, thereby 
allowing a radiation beam to escape the device.  In addition, the licensee's 
survey failed to determine that the radioactive source was not safely 

No written response to this notice is required.  If you need additional 
information regarding these subjects, contact the regional administrator of 
the appropriate NRC Regional Office. 

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