A pavement collapse at Oak Ridge National Laboratory in early June was a significant distance from an area where uranium-233 is stored at Building 3019, the U.S. Department of Energy said Monday.
The collapse of about 36 square feet of pavement was near Building 3019B, which is an inactive facility, the DOE Oak Ridge Office of Environmental Management said.
The hot cells in the facility were not affected, and they do not contain radioactive material, DOE said.
“There were no immediate safety hazards to personnel, but as a precaution, the area was barricaded until crews made repairs,” DOE said.
Uranium-233, or U-233, is a fissionable material, and Building 3019 area is a secure and controlled area. The pavement collapse was reported by the Defense Nuclear Facilities Safety Board on June 19.
The DNFSB said the area of the building that was affected is near the deactivated hot cell, but it is structurally separate from the part of the building where the legacy U-233 materials are stored.
DOE said there were no injuries or damage to the buildings or vehicles. While the affected area was much smaller, a larger area, measuring approximately 50 feet by 25 feet, was excavated to provide a safe working area for repairs.
The DNFSB said the excavation work was done by workers from UT-Battelle, which manages ORNL for DOE’s Office of Science.
UT-Battells and Isotek Systems LLC, a contractor to DOE’s Oak Ridge Office of Environmental Management, determined that the pavement collapse was caused by leaking sections of underground storm water and sewer lines that caused soil in the area to wash away.
“They also noted, via video taken by a subcontractor, that the impacted area extended some distance below the foundation of the facility,” the DNFSB said.
DOE said the extent of erosion under the facility was approximately five feet by seven feet, and it did not extend under the hot cells in Building 3019B.
“The area was also a significant distance from the U-233 storage area,” DOE said.
Isotek management declared a potential inadequacy in a safety analysis due to the possible impact to the safety-significant hot cell structure and restricted access to the affected area of the facility, the DNFSB said.
In mid-June, Isotek workers filled the excavated space, including the areas under the Building 3019 facility, with grout.
“Isotek is also planning work to further stabilize the ground in the immediate vicinity of the facility,” the DNFSB said. “Isotek safety basis staff are developing the unreviewed safety question determination and the evaluation of safety of the situation.”
DOE said a safety evaluation is conducted as a normal procedure when a potential changed condition occurs at a nuclear facility.
“The evaluation determined no additional controls are required to maintain nuclear safety in the Building 3019 Complex,” DOE said in its response, which was provided by spokesperson Ben Williams.
UT-Battelle replaced the storm water and sanitary sewer lines that collapsed, the DOE response said.
“The grout is the first step in the final repair, and follow-on restoration activities are being planned,” it said.
Uranium-233 is a radioactive isotope of uranium that does not exist in nature but can be produced by bombarding thorium-232 with neutrons.
DOE has said the U-233 is stored in very secure vaults in Building 3019 at ORNL.
More information will be added as it becomes available.
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