The following event was received from the state via e-mail:
On October 5, 2009 at approximately 1030, radiographers working for Stork Twin City Testing in a tunnel at a steam plant in St. Paul,
Minnesota were unable to retract the 75 curie
Iridium-192 source (serial number 56177B) of their
AEA Model 660B exposure device (serial number 2657). The radiographers had the device placed on a ladder approximately six feet off the ground during this and two previous exposures. Following several attempts to retract the source the device fell from the ladder landing on the control cable. The Radiation Safety Officer was contacted at approximately 1045. The radiographers established boundaries of approximately 2 mR/h and maintained control over the area. The Radiation Safety Officer placed several layers of
lead over the device and the cable to reduce the exposure levels, but he still considered the levels too high to safely work on releasing the source.
Minnesota Department of Health (
MDH) Radioactive Materials Unit was notified at approximately 1215. The University of
Minnesota's Health Physics staff was contacted and offered to bring additional
lead shielding to the area.
MDH and University of
Minnesota staff arrived at the location at approximately 1250. Following placing additional shielding around the device the Radiation Safety Officer made another attempt to release the source, but was unable to get the source back into the device.
QSA Global was contacted for technical support at approximately 1430. At approximately 1530 the Radiation Safety Officer removed two pins from the back of the exposure device and was able to manually pull the cable and secure the source in the device. Following surveys of the device to determine the source was in the device, the control cable was examined. Damage to the cable at the point where the metal tip connects to the cable was discovered. The exposure device was transported back to Stork Twin City Testing and will be inspected and tested October 6, 2009. The Radiation Safety Officer will submit a complete report to
MDH within 30 days. Personal dosimetry readings were 90 mR for the Radiation Safety Officer and approximately 80 and 30 mR for the radiographers.