Radioactive material stored at the top US nuclear laboratory is safe despite a threatening wildfire which has closed the Los Alamos National Lab (LANL) until Wednesday and forced thousands to evacuate, officials said. \"All nuclear and hazardous materials, including those at the lab\'s principal waste storage site known as Area G, are accounted for and protected,\" authorities said Tuesday on the official New Mexico Fire Information website. \"Water tanks at the lab\'s wild land fire helicopter landing pad are re-filled in preparation for today\'s firefighting activities,\" they said about the historic lab where the atomic bomb was developed during World War II. The laboratory\'s website confirmed that the facility would remain closed until at least Wednesday, and that firefighters have ordered thousands to evacuate the nearby town of Los Alamos, where 42 percent of the lab\'s 11,800 employees live. \"Only employees on an essential-duties access list will be permitted back onto laboratory property during the closure, as notified by their line management,\" LANL said. The Las Conchas fire did not reach lab property Monday night after a small fire on the property was put out earlier that day, and no releases of radiological or other contaminants had been detected by LANL monitoring teams, officials said. \"We ordered the evacuation yesterday after the fire moved beyond our safety triggers and did a small incursion into LANL property that was aggressively fought by our county personnel with LANL support and the forest service helping us to extinguish the small area restoring our line,\" Los Alamos Fire Department\'s assistant chief Michael Thompson told AFP. \"Today we have predictions of more winds that will carry the fire further in the forest above the community and threaten the line that we have (protecting) LANL. We have had some time to prepare for this and now have the resources ready and will defend against the threat,\" he added. Radioactive materials are stored at the Laboratory for research purposes and the property also houses radioactive waste. LANL is operated by Los Alamos National Security, a partnership between the University of California, Bechtel National, the Babcock & Wilcox Company, and the Washington division of URS for the US Department of Energy. Separately, US nuclear authorities were watching floodwaters threatening a nuclear power plant in Nebraska after a protective barrier collapsed. The 2,000-foot (607-meter) long barrier, holding back floodwaters from the Missouri river, collapsed early Sunday, threatening the Fort Calhoun nuclear power plant. \"This allowed floodwaters to surround the auxiliary and containment buildings, which are protected by design to a floodwater level of 1014 mean sea level,\" the US Nuclear Regulatory Commission said. The Missouri river was at 1,006.3 feet (306.7 meters), but river levels were not expected to exceed 1,008 feet, it added in a statement. The collapse \"also allowed floodwaters to surround the main electrical transformers,\" it said, adding that operators transferred power from offsite sources \"as a precautionary measure.\"