(CNN) -- The chairman of the Nuclear Regulatory Commission is expected Monday to visit a Nebraska power plant surrounded by Missouri River floodwater.
The Fort Calhoun Nuclear Station, about 20 miles north of Omaha, Nebraska, is one of two in the state that has been getting increased attention from the Nuclear Regulatory Commission amid historic flooding along the Missouri River.
The Fort Calhoun plant, which has been shut down since April for refueling, has as much as two feet of water in places.
The plant's parking lot is among the areas flooded, requiring plant workers to navigate a catwalk to reach the plant.
The other plant, Cooper Nuclear Station, sits on higher ground and continues to operate.
NRC Chairman Gregory Jaczko is scheduled to visit the Fort Calhoun plant on Monday morning.
Although an inflatable water-filled structure called an aqua berm surrounding the plant was punctured by machinery early Sunday morning, key areas of the facility are not in danger of being flooded, the NRC and the owner of the Fort Calhoun plant said.
"The plant is still protected. This was an additional, a secondary, level of protection that we had put up," said Mike Jones, a spokesman for the Omaha Public Power District. "The plant remains protected to the level it would have been if the aqua berm had not been added."
Plant workers briefly switched to diesel backup generators to keep nuclear fuel at the site cool because water had gotten too close to electrical transformers, Jeff Hanson, a spokesman for the utility, said Monday. The plant was again drawing power from the electrical grid, he said.
In addition to the berm, authorities have put in place floodgates, sandbags and other barriers to help protect the facility. As precautions, workers have been given satellite phones and extra food is stockpiled at the plant according to the NRC.
Plant managers also have brought in additional diesel fuel should the site lose electricity, according to the NRC.
The aqua berm -- an 8-foot-tall, water-filled berm, 16 feet wide at its base -- surrounded the reactor containment structure and auxiliary buildings, according to the NRC.
A representative of the manufacturer is at the plant helping assess whether the berm can be repaired, Hanson said.
With or without the berm, the chances of floodwater getting into the building where the core is kept are almost zero, said Dave Van Der Kamp, with the Nebraska Public Power District.
The plant is designed to withstand water up to 1,014 feet above mean sea level, according to the Omaha Public Power District. The river currently stands at 1,006.3 feet and is not expected to exceed 1,008 feet, the OPPD said.
"We built the plant up high enough based on history, based on the flooding in the past. If the flood would rise for some reason above that level we have taken precautions, again, per our procedures to sandbag the important equipment for the reactors," Van Der Kamp said.
It was catastrophic flooding from Japan's March 11 tsunami that knocked out cooling systems at the Fukushima Daiichi nuclear power plant, resulting in three reactors melting down and producing the worst nuclear disaster since Chernobyl. This year's Midwestern flooding has also led to a spate of rumors about the Fort Calhoun plant that OPPD and the NRC have been trying to knock down.
The utility has set up a "flood rumor control" page to reassure the public that there has been no release of radioactivity from the plant. An electrical fire June 7 did knock out cooling to its spent fuel storage pool for about 90 minutes, but the coolant water did not reach a boiling point before backup pumps went into service, it has said.
Heavy rainfall in Montana and North Dakota, combined with melting snow from the Rocky Mountains, have sent the Missouri surging downstream this summer. The river washed over and punched through levees in northwestern Missouri, spurring authorities to urge about 250 nearby residents to leave their homes.
The 6 to 12 inches of rainfall in the upper Missouri basin in the past few weeks is nearly a normal year's worth, and runoff from the mountain snowpack is 140% of normal, according to forecasters.
The Missouri River is forecast to remain at record or near-record levels from south of Omaha all the way to Atchison, Kansas, into next week. The flooding is affecting communities in Nebraska, Kansas and Missouri.