As experts in Japan race to stave off an accident at the Fukushima Daiichi Nuclear Power Station, the U.S. nuclear industry says a similar emergency is unlikely to happen in this country.
Even though 23 of the 104 nuclear reactors are of the same General Electric design as the Fukushima reactors causing the crisis in Japan, a nuclear industry spokesman said there are guidelines in the United States that would decrease the likelihood of such a disaster here.
"We think we're pretty well equipped," said Tony Pietrangelo, a spokesman for the Nuclear Energy Institute, an industry lobbying group.
"We do plan for blackouts, earthquakes, and tsunamis," he said. "Clearly what happened in Japan is well beyond what they were designed for. It's highly unlikely but we have a station blackout rule to deal specifically with what happened in Japan. We think we're pretty well equipped."
The 23 General Electric-designed reactors are more than 40 years old and are spread throughout the U.S., in cities such as Toms River, N.J.; Cedar Rapids, Iowa; and Vernon, Vt. To generate electrical power, these nuclear reactors use a boiling water system, known as a boiling water reactor.
These reactors continue to produce heat even after fission reactions have stopped. Normally, water pumps are used to cool them down, but the pumps are powered by electricity.
Following the tsunami caused by the 8.9 magnitude earthquake that struck Japan on Friday, the widespread loss of electricity meant emergency crews had to truck in sea water to cool the reactors.
At the Fukushima plants, 175 miles north of Tokyo, experts told ABC News today that it appears evident that there has already been some damage at the core of one or more reactors.
And if the reactors don't cool down soon, the world could experience another disaster on the scale of the Chernobyl meltdown in 1986.
"We're at tipping point," said Joe Cirincione, a nuclear security expert. "In next 48 hours we will either see the reactors start to cool down, or these last ditch efforts will fail and reactor will spin out of control and we will see melt down at one or more (reactor). Totally unprecedented."
Dr. Michio Kaku, a theoretical physicist, said it's clear that there have been partial meltdowns.
"As a physicist I know that if you see cesium and iodine being dispersed in the air that means core damage," he said.
"Even after a core meltdown it doesn't mean you're going to get an explosion," Kaku said. "But with accumulation of steam and hydrogen gas it may be possible to rupture the vessel and then the containment structure itself, and now you're talking Chernobyl."
In Japan, officials say they believe partial meltdowns had occurred at two reactors at Fukushima Daiichi Nuclear Power Station and that a radiation leak was reported at a plant about 59 miles from Sendai.
Cooling system problems were also reported at a third plant, about 75 miles north of Tokyo.
According to Cirincione, a meltdown at the core in the worst-case scenario would mean temperatures so hot inside the reactor that the fuel rods fuse together "in a radioactive molten mass that bursts through the containment mechanisms and is exposed to the outside."
If that happened, it would spew radioactivity in the air, ground and water. Some of the radioactivity could carry into the atmosphere to the West Coast of the United States.
"In Chernobyl, which happened 25 years ago, the radioactivity spread around the entire Northern Hemisphere," Cirincione said. "It depends how many of these cores melt down and how successful they are on containing it once the disaster happens."