Equipment contaminated with plutonium from the manufacturing of fuel for deep space missions has been removed from the 235-F building at the US Department of Energy’s Savannah River Site, marking a milestone in reducing risk at the South Carolina facility.
The Plutonium Fuel Form (PuFF) Facility, located in 235-F, was used to make fuel spheres and pellets out of plutonium-238 (Pu-238). These were used to power deep space missions, such as the Galileo space probe to Jupiter launched from the Space Shuttle Atlantis in October 1989.
The PuFF Facility contains nine cells of thick concrete walls with shielded windows. An estimated 1500 grams of Pu-238 remain in its shielded cells. Its removal is extremely challenging because of the amount of material involved, the very tight spaces with limited accessibility, and the way in which the spheres and pellets were made, which means the Pu-238 was left in some cells as a very fine particulate dust that is easily disturbed. Material entered the facility in Cell 1 and travelled through the other cells to be made into spheres and pellets, handled with remote manipulators.
The Savannah River National Laboratory is using existing technology and developing new tools to locate and remove the Pu-238 or to fix it to ensure it will not become mobile during decontamination activities. Any Pu-238 and tools containing it will be safely stored for eventual packaging and shipment to the Waste Isolation Pilot Plant in New Mexico for disposal. The material to be removed includes wires and manipulator handles. Operators will work remotely as they pass the items through the cells for removal, after which the cells will be vacuumed and otherwise cleaned to remove the leftover plutonium. DOE Office of Environmental Management workers have practiced cleanup work in a mock-up of 235-F.
“This material removal marks a huge milestone in the multi-year process to reduce the risk and clean up the PuFF Facility cells,” 235-F Project Manager Jeff Hasty said. “We started planning for removal in 2012 and have been preparing the cells since then. Work completed so far in the facility includes removing fixed combustibles, upgrading the fire detection system, de-energizing unneeded electrical circuits, draining and cleaning shield windows after their partial disassembly, and installing light sources.”
Deep space missions require reliable, long-lasting power sources both for propulsion once they are in space and to power experiments and equipment. Radioisotope thermoelectric generators (RTGs), usually powered by Pu-238, have been widely used as power sources in satellites and other space but production of the isotope ceased at Savannah River in 1988 and supplies are now scarce. The USA’s The National Aeronautics and Space Administration currently testing the Kilopower reactor, a uranium-fuelled Stirling engine for use in possible future missions to Mars.