( CNN ) -- A water-filled berm protecting a nuclear power plant in Nebraska from rising floodwaters collapsed Sunday , according to a spokesman , who said the plant remains secure . Some sort of machinery came in contact with the berm , puncturing it and causing the berm to deflate , said Mike Jones , a spokesman for the Omaha Public Power District ( OPPD ) , which owns the Fort Calhoun plant . The plant , located about 20 miles north of Omaha , has been shut since April for refueling . `` The plant is still protected . This was an additional , a secondary , level of protection that we had put up , '' Jones said . `` The plant remains protected to the level it would have been if the aqua berm had not been added . '' Parts of the grounds are already under water as the swollen Missouri River overflows its banks , including areas around some auxiliary buildings , Jones said . In addition to the berm , authorities have put in place floodgates and other barriers to help protect the facility , like sandbags . The 8-foot-tall , water-filled berm , 16 feet wide at its base , surrounded the reactor containment structure and auxiliary buildings , according to the Nuclear Regulatory Commission . `` 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 , '' said Dave Van Der Kamp , with the Nebraska Public Power District . He said the chances of floodwater getting into the building where the core is kept are almost zero . The plant is designed to withstand waters up to 1,014 feet above mean sea level , according to the OPPD . The river currently stands at 1,006.3 feet and is not expected to exceed 1,008 feet , the OPPD 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 nearby 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 . 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 . CNN 's Patrick Oppmann contributed to this report .
The Fort Worth plant remains secure , its website says . Some of the grounds are under surveillance . The plant has been closed since April .