Experts: Three Reactors in Meltdown...but Nuclear Catastrophe 'Unlikely

Water levels dropped suddenly inside a Japanese nuclear reactor Monday, leaving a number of uranium fuel rods completely exposed and further raising the threat of nuclear meltdown. Hours earlier a hydrogen explosion tore through a building housing a separate reactor. The situation at a number of Japanese nuclear plants is perilous right now, but reports are mixed as to how the situation may unfold.

The cascading troubles at the Fukushima Dai-ichi nuclear plant Monday compounded the immense challenges faced by the Tokyo government, already struggling to send relief to hundreds of thousands of people along the country's quake- and tsunami-ravaged coast where at least 10,000 people are believed to have died.

Japanese chief cabinet secretary Yukio Edano said it was "highly likely" that the fuel rods inside all three stricken reactors are melting.

Some experts class this as a partial meltdown of the reactor. One such expert spoke Monday to Fox News' Megyn Kelly, predicting that a complete Chernobyl-like meltdown is unlikely to happen at the quake-damaged plants in Japan:

International scientists say there are serious dangers but little risk of a catastrophe like the 1986 blast in Chernobyl, where there was no containment shells.

And, some analysts noted, the length of time since the nuclear crisis began indicates that the chemical reactions inside the reactor were not moving quickly toward a complete meltdown.

"We're now into the fourth day. Whatever is happening in that core is taking a long time to unfold," said Mark Hibbs, a senior associate at the nuclear policy program for the Carnegie Endowment for International Peace. "They've succeeded in prolonging the timeline of the accident sequence."

It is "unlikely that the accident would develop" like Chernobyl, Yukiya Amano, director general of the International Atomic Energy Agency (IAEA), told a news conference Monday, noting several differences, including the design and structure of the nuclear plants.

The earlier hydrogen explosion actually lessened pressure building up inside the troubled reactor and officials insisted the reactor's thick concrete containment shell had not been damaged.  In addition, officials said radiation levels remained within legal limits, though anyone within 12 miles of the plant was ordered to remain indoors as a safety precaution.

"We have no evidence of harmful radiation exposure," deputy Cabinet secretary Noriyuki Shikata told reporters, despite some 190 people having been exposed to some radiation from the plant, including 17 U.S. military personnel involved in helicopter relief missions who were found to have been exposed to low levels of radiation.  U.S. officials said the exposure level was roughly equal to one month's normal exposure to natural background radiation, and the 17 were declared contamination-free after scrubbing with soap and water.

Nuclear safety officials have confirmed that monitoring devices surrounding the plant briefly showed elevated radiation levels but they have since gone down.  But as a precaution, the U.S. said the carrier and other 7th Fleet ships involved in relief efforts had shifted to another area.

On Saturday, a similar hydrogen blast destroyed the housing around the complex's Unit 1 reactor, leaving the shell intact but resulting in the mass evacuation of more than 185,000 people from the area.

Despite experts' assessments, many residents across the region are fearful of the situation.

People in the port town of Soma had rushed to higher ground after a tsunami warning Monday — a warning that turned out to be false alarm — and then felt the earth shake from the explosion at the Fukushima reactor 25 miles (40 kilometers) away. Authorities there ordered everyone to go indoors to guard against possible radiation contamination.

"It's like a horror movie," said 49-year-old Kyoko Nambu as she stood on a hillside overlooking her ruined hometown. "Our house is gone and now they are telling us to stay indoors.  "We can see the damage to our houses, but radiation? ... We have no idea what is happening. I am so scared."

The Associated Press contributed to this report.