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Added flood protection at Nebraska nuclear plant fails
A concerning situation near Omaha, Neb. took a new twist early Sunday when a temporary levee protecting the Fort Calhoun Nuclear Station failed, forcing the facility to turn briefly to emergency generated power.
Two Nebraska nuclear stations — Cooper near Brownville and Calhoun near Blair (19 miles north of Omaha) — are coping with ongoing Missouri River flooding. Although Cooper was built above the flood plain, Calhoun was not. As a result, Cooper continues to operate, while Calhoun, which shut down for refueling in April, remains offline.
Workers with Omaha Public Power District, owners and operators of Calhoun, had placed a massive AquaDam around the structure and its other flood protection systems. The AquaDam, a tube structure filled with water that was eight-feet tall and 16-feet wide, was punctured early Sunday morning during onsite work.
“Some mechanical equipment tore the side of the dam,” Victor Dricks, Region 4 spokesman for the Nuclear Regulatory Commission, told The Iowa Independent Monday by phone. “As a result, the plant switched to emergency power for a period of a about 12 hours.”
NRC inspectors were onsite when the incident occurred, and flood waters rushed auxiliary and other buildings at the site. The power supply was cut because water infiltrated the plant’s main electrical transformers. Power has since been switched away from emergency generators and to an off-site power supply.
Keeping power at the plant is critical since the reactor core has been refueled and spent fuel remains in a cooling pool. Dricks said the failure of the dam did not adversely impact either the core or the cooling pool. Dry cask storage of spent fuel has long been exposed to the flood waters and, as Dricks told The Iowa Independent last week, poses no risk.
Other, more solid berms were located inside the area also being protected by the AquaDam. Those protections are holding with minor seepage and, of course, additional rainfall being pumped away from the structure and back into the river.
“We do not expect the river would rise to a level that would threaten the cooling pool or the core,” Dricks said.
The Calhoun plant was built at 1,004 feet mean sea level, and can sustain flood waters up to 1,014 feet. On Sunday, when the dam broke, the Missouri River was at roughly 1,006.5 feet near the Calhoun station. If floodwaters reach 1,009 feet, the plant would likely switch from the lowest level of emergency status (where it has been since June 6) to the second of four emergency levels. Based on the latest figures given by the U.S. Army Corps of Engineers, which is gauging the release of water from dams upstream, flooding near Calhoun should peak at 1,008 feet.
In addition, workers at Calhoun are adding to the height of existing levees, hoping to strengthen the existing structures before waters rise near their peak of 1,011 feet.
As The Iowa Independent previously reported, both Cooper and Calhoun have stockpiled supplies of fuel for emergency generator power. Dricks said Monday that arrangements had been made for even more fuel to arrive by boat or aircraft if needed, both for the emergency generators and for pumps removing water from inside the levees.
Worst-case scenario plans are also in place if floodwaters should reach 1,014 feet, breech the levee and prohibit further use of emergency generators. In that highly unlikely circumstance, plant officials would tap into power lines running above the facility and/or utilize secondary backup generators housed at 1,036 feet.
Before floodwaters could flow into the cooling pool the river would need to rise to an incredibly unprecedented 1,038.5 feet.
Much of the good fortune at the plant during this crisis has been the result of earlier inspections by regulatory officials that revealed several imperfections in relation to flood preparedness at the plant. Because of the inspections and subsequent work by OPPD officials, many of problems that could have spelled catastrophe during this flood have been mitigated. OPPD workers first began flood prevention activities during the weekend of May 21.
Gregory Jaczko, chairman of the NRC, toured Cooper late last week, and indicated that the plant was operating safely and according to standards. Jaczko is scheduled to be at the Fort Calhoun site Monday for an official plant inspection at that location.