In OE Weekly Summary 93-47, ONS reported an occurrence at the Pantex Plant on November 16, 1993, when radiation safety personnel discovered the loss of a 0.005- microcurie thorium-230 instrument check source. The check source, electroplated on a 7/8- inch-diameter stainless-steel disk, was attached to a source holder on a hand-held radiation monitor. The check source became detached from the holder, which remained affixed to the radiation monitor. After conducting extensive instrument and visual searches of the vehicle and areas where it was transported, facility personnel determined that the source was lost. Site personnel indicated there was minimal potential for removable contamination from the source. (ORPS Report ALO-AO-MHSM-PANTEX-1993-0060)
In response to a similar event at their facility, Radiation Safety personnel at the Idaho Chemical Processing Plant (ICPP) designed an improved storage device for small, low-level radioactive disk-shaped sources. The event occurred on March 4, 1992, when a 0.0051 microcurie plutonium-239 source used to check constant air monitor instruments fell out of a wooden box and onto a gravel parking area while being transferred to a new secured storage area. Two days later, an employee noticed what appeared to be a quarter, picked it up, and noticing the source markings, immediately turned it over to Health Physics personnel. Radiation Safety personnel performed surveys of the individual who found the source, the area where it was found, and the source itself. They found no contamination. (ORPS Report ID--WINC-ICPP-1992-0025)
Investigators determined that the direct cause of the event was failure of the latch on the wooden source storage box to keep the box door closed during the transfer. In addition, because the box was made of wood, facility personnel did not know the source was missing. As part of corrective action to prevent similar events, facility personnel designed a transparent source storage box that allows verification of the presence of the source without opening the box and also has a unique positive locking device to prevent the source from inadvertently falling out. The box, called the "C-THRU Source Box," is made of lexan and consists of a source holder that swings out from the main body of the box when needed and when the positive locking device is disengaged. The source holder can be fabricated to hold different sized source disks.
As a result of information sharing by ICPP personnel, the device is also in use, or is being considered for use, at other DOE sites including Rocky Flats, Hanford, Savannah River, and Waste Isolation Pilot Plant. The actions taken by the ICPP Radiation Safety personnel provide an excellent example of how sharing operating experience and lessons learned from events can improve the safety of operations and help prevent occurrences at all DOE facilities. For more information on the source storage box designed by ICPP, contact Dave Fullmer, WINCO, at 208-526-5724.
DOE requirements for radioactive source control are specified in Article 431 of the DOE Radiological Control Manual (DOE/EH-0256T) and DOE N 5400.9, Sealed Radioactive Source Accountability.