(CNN) -- A complete loss of electrical power at a nuclear plant, as occurred at Japan's Fukushima Daiichi facility, is the greatest potential risk to U.S. nuclear reactors, industry experts said Tuesday.
They cited hurricanes, tornadoes and ice storms as threats beyond earthquakes that could cripple a nuclear facility by cutting power needed to keep pumping water and cool nuclear fuel rods.
There is a vulnerability and we need to take steps to lessen the vulnerability in the U.S.," said David Lochbaum, Director of the Union of Concerned Scientists Nuclear Safety Program.
The leading trade group for the industry, The Nuclear Energy Institute, agreed that is the primary problem facing operators of the Daiichi plant in Japan, who are fighting to avoid a catastrophic meltdown.
"Until they restore A/C power, like they did at (Fukushima) Dainai, we'll be in the current situation," with the threat of greater release of radioactive material into the atmosphere, said NEI's Chief Nuclear Officer, Anthony Pietrangelo.
After the massive magnitude 9.0 earthquake knocked out the electrical grid powering Fukushima Daiichi, emergency diesel generators provided power for just one hour before a tsunami washed away the plant's diesel fuel tanks and flooded critical switching gear, said the NEI.
Nuclear plants in the United States are required to plan for so-called station blackouts under a Nuclear Regulatory Commission rule. Some plants in the U.S. try to protect their diesel generators by placing them underground.
If backup diesel generators fail, battery power is available as a secondary backup, though that power source will last no longer than 12 hours.
U.S. nuclear officials say they want to study the Japanese crisis carefully to glean any lessons for making power plants safer, but that such analysis is a long time away.
"We're not going to pretend we understand everything that's going in there," said Pietrangelo, urging patience before any changes are imposed on operations and licensing of facilities in the United States. "There will be plenty of time to make policy decisions going forward."
The industry says nuclear plants in the U.S. are well constructed to handle maximum anticipated seismic activity and tsunamis.
"We think we're on bedrock in terms of how we design and license these plants," said Pietrangelo. "We've very confident in terms of the robustness of these plants."