WOODRUFF: As the drama continued in northern Japan, Americans were reminded of our own near nightmare, the 1979 Three Mile Island accident.
(UNKNOWN): Radioactivity is 75 times a dose that would be lethal to a human.
WOODRUFF: That meltdown is still considered the most serious accident in U.S. nuclear power plant history, causing widespread panic, as 140,000 neighboring residents chose to evacuate.
In the end, no one was injured, but experts say disaster was perilously close. The worst-case scenario, however, came seven years later in the Soviet Union.
JENNINGS: There has definitely been a meltdown at the nuclear reactor in Chernobyl.
KAKU: By far, the worst accident was Chernobyl, which was the biggest explosion, biggest collapse, the only real core fire that we've ever had that spewed tons of radioactive material in the atmosphere and around the globe.
WOODRUFF: In the end, experts estimate at least 4,000 were killed, both by the immediate disaster and by radiation-related diseases in the years to come. The Chernobyl plant, however, lacked a protective concrete shell that is considered to be crucial for safety in Europe, Japan and the U.S.
KAKU: Three Mile Island ended nuclear power construction in the United States. Chernobyl ended most nuclear power construction around the world.
WOODRUFF: In the years since, safety has greatly improved. Thirty years after the accident at his plant, the current manager of Three Mile Island assured me a repeat of 1979 would be extremely unlikely.
(on-screen): That kind of melting is not going to happen again?
(UNKNOWN): That's correct.
WOODRUFF: There's no way?
(UNKNOWN): That's correct. These plants are extremely robust. The safety systems are tested frequently.
WOODRUFF (voice-over): But the disaster in Japan could again sway public opinion against nuclear power, despite the industry's insistence that safety is better than ever.
Bob Woodruff, ABC News, New York.
AMANPOUR: Joining me now to discuss all of this is, nuclear expert Joe Cirincione of the Ploughshares Fund and ABC's Jake Tapper and Martha Raddatz.
Let me start with you first, Mr. Cirincione. How bad is this nuclear meltdown, for want of a better word, and the fears that there may be another explosion here at one of the reactors?
CIRINCIONE: This is already one of the worst nuclear accidents in history if it stops right now. And we're dealing with multiple meltdown possibilities at reactor number one, at reactor number two at the Daiichi site. There's also concern about reactors at the Daini site. There were actually incidents at other nuclear facilities in Japan that would have been significant incidents by themselves, but they're caught in the wake of these major crises at these nuclear reactors that possibly will melt down in the next couple of days.
AMANPOUR: Jake, how worried is the U.S. administration that this could reach the United States?