The following is excerpted from an email/fax received from the U.S. Navy, Radiological Controls Office:
An irradiator located as Naval Surface Warfare Center, Carderock on 16 November [2016] at approximately 1500 [EST] malfunctioned.
During routine use of the JLS 81-20 self-shielded irradiator (Co-60 source with all attenuators 1000, 100, 10, 1, 2, in place) the device did not terminate the shot at the end of the exposure period. The end-user attempted to use the emergency stop at the control panel, which did not work as intended. The panel displayed the source was in "MOVEMENT" status for approximately 70 minutes.
No injuries or overexposures occurred, there seems to be an operational issue with the irradiator source moving from an exposed position to the shielded position, which Carderock is taking steps to correct. They have verified the source returned to the shielded position and have placed the calibrator out of commission until maintenance can be performed.
The licensee has notified the NRC Project Manager (Seeley).