Robotics Use in Source Recovery at the Savannah River Site
C. W. Lewis
The Department of Energy's Savannah River Site (SRS) in Aiken, South Carolina has a state-of-the art Instrument Calibrations facility that supports calibration and repair of an inventory of approximately 8000 portable radiological monitoring instruments. The instrument calibrations facility began operations in 1996. The Low Scatter Irradiator (LSI) system is a key part of the facility. The LSI room is a shielded 40-foot by 40-foot by 40-foot room designed to minimize radiation scatter during calibrations and evaluations. Aluminum floor grating with one-inch spacing is part of the design to minimize scatter. A shielded source storage carousel is used to select calibration sources via a computer-controlled system. The carousel has eight source slots with seven sources used providing a selection of Co-60, Cs-137, and Cf-252 sources of different intensities. One slot is used for a dummy source for system function testing. Sources are contained in an aluminum container known as a source rabbit. Air pressure is used to blow the selected source through a transfer tube to the top of the tube where it is held in place by a suction cup and a maintained air vacuum. During calibrations, instruments are placed on four LSI tracks that move instruments to the proper distance from source for the desired calibrated exposure rate. Sources are returned to the carousel using gravity with multiple interlocks and safeguards built into the system to ensure that the source has dropped before entry into the LSI after a source exposure. Two room radiation monitors provide a remote reading to the operator from the computer console as another indicator of the source status. Due to the design of the LSI, it was assumed that a source could not become lodged in the transfer tube. That proved to be a false assumption when in May 2000, a source did not return to its home position. This paper focuses on the recovery operations for the exposed source with a summary of each step.
This abstract was presented at the 34th Annual Midyear Meeting, "Radiation Safety and ALARA Considerations for the 21st Century", ALARA Session, 2/4/2001 - 2/7/2001, held in Anaheim, CA.