The remnants of the University of Arizona's nuclear reactor are now entombed in concrete beneath the historic Engineering Building, leaving the campus as mildly radioactive as it has always been.
"You're on a radioactive planet," said Robert Offerle, acting director of the reactorless UA Nuclear Reactor Laboratory. "This is a radioactive building, and you can buy radioactive bananas over at the U-mart."
Offerle, who oversaw the final decommissioning of the UA's 52-year-old TRIGA reactor this year, said he has always gotten higher readings from the natural radioactivity of the red bricks of the Engineering Building than from the reactor room.
Bananas, valued as a healthy snack because they are rich in potassium, contain minute amounts of the radioactive isotope potassium-40.
The UA research reactor never produced radiation readings above background levels in its 52 years of operation, Offerle said. The decommissioning went smoothly as well.
"We did it on time, on budget, with no injuries, no goofs, no pinched toes, no bleeding, nothing," he said.
There were surprises along the way:
• Technicians dropped a fuel rod while moving it out of the core. "They are built to withstand that sort of thing," Offerle said.
Offerle devised a "lariat," with construction twine and a couple of washers, and managed to snare the top of the rod through the 20 feet of water in the tank and lower it into a holding slot. "It was fun fishing for fuel," he said. "There is no book, no manual and directions for how you retrieve a fuel rod," he said.
• After the Department of Energy removed the fuel from the reactor last December, contractors working with LVI Environmental Services drained the tank of the demineralized water that had shielded operators from the reactor core. Two "geckos" that operators thought were lying on the bottom of the tank turned out to be dust bunnies.
• The tank itself was more substantially encased than the construction plans indicated.
The decommissioning plan had proposed chipping away the gunite that lined the stainless steel tank, and then removing the bottom 6 feet of steel, along with the concrete in which it sat and any surrounding soil that was radioactive.
The concrete surrounding the tank was up to three times thicker than anticipated, and there was no way to safely support the upper 15 feet of concrete and steel while workers removed the bottom 6 feet, Offerle said.
Fortunately, said Offerle, the tank was intact, the concrete only mildly radioactive and the soil not affected.
The U.S. Nuclear Regulatory Commission approved a plan to remove the steel and a portion of the concrete, which was boxed and shipped to a nuclear waste depository.
Radiation levels in the remaining concrete were well below those required by the Nuclear Regulatory Commission, Offerle said, and, on average, four times below the more stringent levels set by the Environmental Protection Agency.
The hole was filled with fresh concrete in early October, and a "Final Status Survey Report" was drawn up by the consulting firm Enercon.
It is under review by university officials, who expect to be able to use the about 2,000 square feet of reactor, control and storage rooms for labs or offices.
"I've gotten lots of calls on that space," said Jeffrey Goldberg, dean of the College of Engineering. The college currently rents space off-campus for labs.
Goldberg said the windowed-room that once held the reactor and control room would make a good "display lab." Upstairs from the reactor, the former storage space could accommodate meetings between undergraduate students and teaching assistants, he said.
An additional 2,000 square feet of offices will also be vacant, as five positions are eliminated.
Offerle, 62, is joining former director John Williams in retirement.
AT A GLANCE
The University of Arizona research reactor, installed in 1958, was a light-water reactor fueled with 20 percent enriched uranium in a zirconium hydride matrix.
The fuel rods, each about 28 inches long and 1 1/2 inches in diameter, sat in a water-filled tank, 21 feet below the ground floor of the UA's historic Engineering Building, built just north of Old Main in 1918.
The reactor is called a "TRIGA," a trademark standing for Training Research Isotope-production General Atomics. The UA facility was the first of more than 60 TRIGA reactors installed worldwide.
The UA reactor did not generate electricity. It was used for reactor-dynamics research; neutron-activation analysis of mineralogical samples such as meteorites; radiation-effects testing; processing of electronic materials; and isotope production for biomedical and other research.
Contact reporter Tom Beal at firstname.lastname@example.org or 573-4158.