No one was injured when chunks of concrete weighing up to 20 pounds fell from the ceiling in a roped-off area in a building at the Y-12 National Security Complex in March.
That area of Building 9204-2 in Y-12‘s production area had been roped off to restrict worker access. The controlled area has been in place since 2009, said B&W Y-12, the plant’s managing and operating contractor. Access to the area was controlled with marker tape and boundary markers.
When the ceiling fell in that part of the building, large chunks of concrete rebounded into a frequently used walkway and an adjacent welding station, the Defense Nuclear Facilities Safety Board reported in the week ending March 21. Workers had used the welding station earlier in the day, the DNFSB said.
B&W Y-12 said chunks of the concrete fell to the floor and struck a portable welding exhaust unit located inside the controlled area. Some small pieces of the concrete also scattered outside of the area. Personnel in a nearby area heard the noise, discovered the problem, and immediately notified the shift manager, per procedures, the contractor said.
“No personnel were injured,” B&W Y-12 said.
The DNFSB reported that concrete debris rebounded about 20 feet from the area directly under the location of the spalled concrete. Some of the concrete chunk were more than one foot in diameter and two inches thick. In total, the affected area on the ceiling was about eight feet long and three feet wide, the board said.
“The rebar in this area was severely corroded and residual pieces of rebar fell with the spalled concrete to the floor,” the DNFSB said. “B&W reported this event as a ‘near miss’ and has started actions to understand the extent of condition.”
B&W Y-12 said there was minor damage to the welding exhaust unit, and an abandoned drain pipe also was damaged. No damage was noted to nearby equipment, but the equipment was de-energized and isolated as a precautionary measure, the contractor said.
The incident was cited by U.S. Rep. Chuck Fleischmann during a recent House subcommittee hearing that included testimony by Bruce Held, who was then acting administrator of the National Nuclear Security Administration.
Flesichmann said the conditions of some of the World War II-era buildings at Y-12 are “sad,” “deplorable,” and “antiquated.” Y-12 was built during the war to enrich uranium for the world’s first atomic weapons, and there are efforts under way to modernize its facilities, including by building a new multi-billion-dollar Uranium Processing Facility.
The DNFSB said a B&W structural engineer wrote a repair plan for the Building 9204-2 ceiling in April 2013. That plan was based on a 2009 inspection that found serious delamination and potential spalling of the concrete slab.
“The engineers that had performed the inspection noted signs of extensive corrosion of the concrete and steel rebar,” the board said. “They concluded that this corrosion was caused by Kathene (aqueous lithium chloride) from a dehumidification unit on the floor above the area in question. This unit has been drained and out of service since 1988. The repair plan was not implemented due to resource constraints, but the floor immediately under the area of concern remained roped off and posted with signs requiring personnel to contact the shift manager and don a hard hat prior to entry.”
The DNFSB said a site representative walked down that area of Building 9204-2 with a NNSA Production Office facility representative and B&W structural engineers after the ceiling fell. In addition to the follow-up actions, NPO management is also drafting a letter to outline “additional expectations regarding B&W’s response to the event,” the board said.