The pictures of a Nebraska nuclear power plant were startling: Floodwaters from the swollen Missouri River had risen nearly to the reactor building, with the potential to climb even higher.
Coming only a few months after Japan's nuclear disaster, the Associated Press images alarmed many people who saw them earlier this week. But nuclear regulators and the utility that runs the Fort Calhoun reactor say there is little cause for immediate concern.
The plant, encircled by a giant rubber barrier against the water, has been shut down since April. The Omaha Public Power District says the complex will not be reactivated until the flooding subsides.
And unlike Japan's infamous Fukushima Dai-ichi facility, the entire plant in Nebraska still has full electrical power for safety systems, including those used to cool radioactive waste. It also has at least nine backup power sources.
The Fort Calhoun complex "is safe and it will continue to be safe throughout this flooding situation," said Dave Bannister, chief nuclear officer for the power district.
A spokesman for the Nuclear Regulatory Commission reinforced that view. "We think they've done everything that they need to do to respond to the current conditions," Victor Dricks said.
Flooding remains a concern all along the river because of the massive amounts of water released by the Army Corps of Engineers. The river is expected to rise as much as 5 to 7 feet above flood stage in much of Nebraska and Iowa and as much as 10 feet over flood stage in parts of Missouri.
The corps expects the river to remain high at least into August because of heavy spring rains in the upper Plains and substantial Rocky Mountain snowpack melting into the river basin.
After fielding many worried questions about the plant, utility officials held a news conference Friday to reassure the public.
"We understand the deep responsibility we have in operating a nuclear power plant," CEO Gary Gates said.
Edwin Lyman, a physicist with the Union of Concerned Scientists, said plants at risk from floodwaters must ensure their electrical supply and coolant pumps are protected.
"There's no question that flooding can be an extremely serious concern," Lyman said.
The pumps are a key piece of safety equipment because if pumping systems fail for several days and are not fixed, cooling water could boil away and eventually cause radioactive releases.
Workers at the facility 20 miles north of Omaha are still able to get inside the building without getting wet by using walkways that rise above the water.
The river has risen 1.5 feet higher than Fort Calhoun's 1,004-foot elevation above sea level, but the water is being held back by a series of protective barriers, including an 8-foot rubber wall outside the reactor building.
Fort Calhoun can be fortified to handle water up to 1,014 feet above sea level, Bannister said.
In another contrast to the March 11 tsunami in Japan, the Missouri River flooding has been predicted for weeks, so there was plenty of time to prepare. But even if the river had risen in a flash flood, Fort Calhoun's reactor building is designed to handle water up to 1,007 feet above sea level before any additional floodgates or barriers are added.
The rubber barrier surrounding the plant is designed primarily to protect external equipment, not the reactor itself, which Banister said is encased in a watertight room. The building housing the reactor has been fortified with steel plates on the outside and a series of internal barriers.
The pool that holds radioactive spent fuel is in an elevated structure several stories above the rest of the power plant, so the waste is well protected from floodwaters.
The spent fuel stored in dry casks is in an area that's 1,009 feet above sea level.
Last year, the regulatory commission criticized Fort Calhoun's flood response plan because the utility had a large supply of sandbags, but no sand to fill them. The utility remedied that problem by stockpiling thousands of filled sandbags.
Regulators did not find any significant deficiencies in the flood plan when Fort Calhoun was inspected this spring after the nuclear crisis in Japan.
The utility started buying sand and other supplies weeks ago after learning of the corps' plan to increase the amount of water flowing down the river, Bannister said.
To help ensure Fort Calhoun remains safe, regulators increased their presence at the plant from two to six inspectors, so at least one is always there.
The agency concluded that both the Fort Calhoun plant near Blair and the Nebraska Public Power District's Cooper plant near Brownville are safe.
"We think both plants are taking appropriate action," Dricks said.
The Cooper plant remains dry and is less of a concern because it is further from the river. Cooper is at 903 feet elevation, and Dricks said the river there is not predicted to climb above 900 feet.
But utility officials are monitoring the river levels closely and have installed some barricades around the plant as a precaution.
The river would have to climb to 902 feet at Brownville before officials would shut down that plant.
Nuclear Regulatory Commission: www.nrc.gov
Omaha Public Power District: www.oppd.com
Nebraska Public Power District: www.nppd.com