Japan's reactor crisis has renewed anxiety about nuclear safety and could derail efforts to revive the U.S. industry as a clean alternative energy source.
The failure of the Japanese reactors' backup cooling systems and the explosions that followed are likely to lead U.S. regulators to re-evaluate nuclear plant designs and safety. The heightened scrutiny could increase costs for new and existing reactors and make it harder to raise money for new plants.
The crisis comes just as the U.S. nuclear energy industry is starting to build the first new reactors in a generation.
"This accident has the potential to tamp down any nuclear renaissance that we're poised to experience," said Tim Echols, a utility regulator in Georgia who supports expanded nuclear power.
Before the crisis, the U.S. nuclear industry was enjoying more public and political backing than it had in years _ 62 percent of the public, according to a Gallup poll done last year. That support grew out of concerns about greenhouse gases, a growing record of safe and profitable nuclear power production and volatile fossil fuel prices.
In Washington, nuclear energy was a rare issue on which the Obama administration and congressional Republicans agreed. President George W. Bush established an $18.5 billion loan guarantee program to help build new plants. President Barack Obama wants to raise that to $54.5 billion. Obama has also included nuclear power in his plan for a clean-energy standard.
Nuclear power generation emits no carbon dioxide, a damaging greenhouse gas. And unlike wind or solar, nuclear reactors produce huge amounts of power, uninterrupted, for months. The 104 commercial reactors in the U.S. supply about 20 percent of the nation's electricity.
But only two of nearly three dozen nuclear plants that were proposed in the middle of the last decade remain on track to be built. Low electricity prices and the huge expense of building new plants have contributed to the delay.
Industry analysts say few, if any, could be built without government loan guarantees, a low-carbon energy mandate, or both. That government help is predicated on support from a public that may have suddenly grown more fearful about the safety of nuclear power after the Japan crisis.
The two projects that appear to be furthest along, both with regulators and financing, are in the Southeast.
The Atlanta-based Southern Co. and its partners are seeking to build two more reactors at Plant Vogtle in eastern Georgia. And SCANA, based in Cayce, S.C., has proposed adding two reactors to its Plant Summer site in Jenkinsville, S.C.
Both utilities have said they expect to be granted operating licenses this year and insist their projects will proceed. The Nuclear Regulatory Commission is still evaluating both. Southern Co. says its proposal passed initial safety reviews, which analyzed how well its reactors could withstand earthquakes, hurricanes, tornadoes, tsunamis _ even a direct hit by a hijacked jetliner.
But nuclear experts and analysts say the Japan nuclear crisis will probably increase uncertainty and costs because of new regulations. It could also rattle investors.
Shares of Exelon Corp., the nation's biggest nuclear operator, have fallen 4 percent this week, to $41.34. Shares of Entergy Corp., the second biggest nuclear operator, fell 7 percent to $68.49.
"When it comes to emergency response, who is better than Japan?" asked Jim Hempstead, a senior vice president in the Global Infrastructure Group at Moody's Investors Service. "And now look what's happened."
Plans for two other U.S. reactors have suffered setbacks in recent months.
NRG Energy wants to add two reactors to its South Texas Project. But the project's future was already in doubt because of low natural gas and electricity prices. NRG's partner on the project, subject to a federal loan guarantee, is Tokyo Electric Power Co., owner of the stricken Japanese reactors.
Constellation Energy and Electricite de France had planned to build a new reactor at Calvert Cliffs, Md., but Constellation backed out of the partnership late last year. It's unclear whether EDF will be able to pursue the plan.
Obama and Energy Secretary Steven Chu have renewed their support for new nuclear power since the earthquake. But some lawmakers are already calling for at least a delay.
Sen. Joseph Lieberman on Sunday expressed his continued support for nuclear power. But he added, "We've got to kind of quietly, quickly put the brakes on until we can absorb what has happened in Japan."
Abroad, the reaction has been more drastic. German Chancellor Angela Merkel has said her country's seven oldest plants will be shut down at least temporarily. Switzerland has suspended plans to build new reactors.
Nuclear advocates counter that if the radiation from the crippled reactors is contained and injuries are minor, the disaster could turn out to help the industry.
The reactors at the Fukushima Dai-ichi Power Station are 30 to 40 years old. They were not designed to handle a natural disaster as punishing as last week's earthquake and tsunami.
"If containment holds on these units, that is something that can be considered a success story," says Paul Murphy, who works in nuclear business development for the law firm Millbank. "The quake was so strong that the earth's axis moved, and this old technology withstood it."
Chu told a House panel Tuesday that reactors in the U.S. have designs beyond what would be required to withstand a worst-case earthquake and tsunami.
And the next generation of reactors is designed to better handle a disaster of the kind that struck Japan. What apparently doomed the Japanese reactors was a loss of backup power needed to cool their fuel rods once the tsunami hit. Newer plant designs are designed to be cooled in an emergency with no need for electricity. One is a Westinghouse Electric Co. design being built in Georgia and South Carolina.
With the newer designs, cooling water is stored above the steel container protecting the reactor. In case of emergency, the water would flow, by force of gravity, onto the containment vessel to cool it.
Such a gravity-powered cooling system can operate for about 72 hours. The steel containment and the surrounding shield building are also designed to cool by using the natural circulation effect created by heated air.
"If you have some sort of hurricane or earthquake or natural disaster, then you have on the site sufficient resources to handle your plant for a period of seven days," says Ed Cummins, a vice president at Westinghouse Electric Co.
U.S. public support for nuclear power could erode after the terrifying images of explosions at nuclear plants beamed from Japan in the days after the earthquake.
The last major U.S. accident, the 1979 partial meltdown of the core of the reactor at Three Mile Island in Pennsylvania, led to only scant releases of radiation and no deaths. Yet it helped turn public opinion against the plants and contributed to a 30-year setback for the U.S. nuclear industry.
Cummins said regulators undertaking a review of the proposed Georgia reactor and plant design could end up hearing more public comments as a result of the crisis in Japan. He also said lawmakers in Congress could put pressure on the NRC to slow the licensing process.
"This will be more than a passing incident," he said.