Even as the world tensely monitors Japan's nuclear crisis, it's clear that nuclear power will face harsher public scrutiny and a reevaluation of nuclear's expansion.

Last week's powerful earthquake and tsunami shut down the Fukushima Daiichi power plant and crippled the cooling systems at three reactors. According to reports, plant operator Tokyo Electric Power Company said that one of the cores, No. 2, has been temporarily exposed to air, risking a meltdown of the nuclear fuel or metal cladding around the fuel rods.

A close-up of a nuclear fuel assembly being placed into a nuclear reactor core at a U.S. power plant. Click for a slideshow of the inside of a nuclear power plant.

As Japanese officials deal with multiple crises from one of the five largest earthquakes in recorded history, the ripple effects from the nuclear power emergency are being felt around the world, shaping public opinion and raising the bar for safety.

"In terms of being a social catalyst, this could change the requirements for using the technology and it could have a big effect," said Michael Golay, a professor of nuclear science and engineering at the Massachusetts Institute of Technology. "To a large extent, it depends on how competent a job the media does."

In the U.S., it's likely that there will be a review of the vulnerability of nuclear power plants to earthquakes, particularly in active zones such as California, experts said. Six reactors in the U.S. use the same design as Fukushima Daiichi, according to the Nuclear Energy Institute, and most of the U.S.'s 104 plants were built in the 1970s and 1980s. In addition to a review of current plants, Congressman Edward Markey yesterday called for a moratorium on new plants in seismically active zones, saying that a quake the size of that in Japan would endanger existing U.S. plants.

Amid public demonstrations, German officials today put in place a three-month moratorium on the extension of operating lives for existing nuclear plants in order to review safety standards. Swiss officials suspended approvals for three new plants to reconsider safety levels and study what happened in Japan. Similarly, India said it will review all nuclear reactors.

At Fukushima Daiichi, engineers are using the improvised technique of pumping seawater into the reactor core to keep temperatures under control. Even though the nuclear plant stopped operating after the quake, residual radioactive material is still generating heat and needs to be cooled for what is called a "cold shutdown."

To lower the pressure from steam in the containment building, engineers are venting steam which contains radioactive versions of cesium and iodine. Japanese officials have created a 12-mile (20-kilometer) exclusion zone so people are not exposed to the low-radiation steam. The release of this radioactivity gas is higher than the normal amounts people are exposed to from the environment but poses "minimal health risks," a World Health representative told AFP.

There have been two explosions at the plant caused by the build-up of hydrogen from the cooling operation, with one occurring today, according to the Japanese government. Neither blast is believed to have damaged the metal shield of the containment dome, which is crucial in keeping radioactive gases and the core contained.

Although it's still an unfolding situation, experts say that the crisis will not result in the same level of damage that occurred in 1986 at the Chernobyl plant in the Soviet Union which was a different design and didn't have a containment dome. The International Atomic Energy Agency said the Chernobyl accident was classified at the highest rating of seven, while the Fukushima Daiichi event, as of Sunday, was classified as Level 4, an "Accident With Local Consequences," lower than the Level 5 rating given to the 1979 Three Mile Island accident.

Last-ditch cooling efforts Using the Three Mile Island accident as a guide, cooling the core with seawater at Japan's Fukushima plant reactors could take several days, said Andrew Kadak, the director of nuclear services at consulting company Exponent and researcher at the Massachusetts Institute of Technology. Venting of steam to relieve pressure could continue on for months, The New York Times reported yesterday.

Four of the Fukushima Daiichi plant&39's six reactors are shown in this satellite photo from Geoeye via Google Earth. The reactors are the four tall buildings inland of the four longer buildings' the Pacific Ocean to the east is on the bottom of this photo. Reactors four, five, and six had been shut down before the earthquake and tsunami, but plant operators are struggling to cool down units one and three and it's believed there has been a partial meltdown in unit two.

The fuel in a nuclear reactor, which is often uranium oxide, is shaped in long thin rods made of individual pellets. To stop the atom splitting that generates heat in a nuclear chain reaction, metal tubes called cladding fit over fuel rods to make what is called an assembly. Dozens of assemblies, each generating heat to make steam to turn an electricity-generating turbine, are placed under water in a core.

What Japanese engineers are furiously trying to avoid is a meltdown where the assemblies in the core are exposed to air for a long time and cannot be cooled. In the case of a full meltdown, the assemblies melt, turning the solid fuel into a lava-like or wax-like fluid.

Japanese officials today said that even in a worst-case scenario, the melted fuel will not cause the type of dangerous radiation exposure that happened at Chernobyl, according to reports. If the containment building remains intact, then radioactive material from the fuel will not leak into environment.

It's possible that the melted fuel would melt through the floor in the containment building, The New York Times reported today. Kadak, however, said that is highly unlikely because there is water in the containment building outside the nuclear reactor core. That means the molten fuel will be able to turn solid and remain there, Kadak said. As in Three Mile Island, the core would be left to decay for several months and then cleaned up, Kadak said.

Weighing risks Because the situation has not yet stabilized and many details on precisely what went wrong when are still not known, it's not clear what lessons nuclear plant operators and regulators can apply from the Fukushima accident, experts said. But the events will certainly inform the public dialogue around nuclear power, said Neil Wilmshurst, the chief nuclear officer at the Electric Power Industry Association, a utility-funded industry research group.

"You have to make an assumption of the maximum earthquake, the maximum tsunami, every external event. Around the world, there's a constant review and update of those designs," he said. "This will be one of those events that will be studied in tremendous detail and will influence decisions going forward."

Opponents to nuclear power were quick draw attention to the health risks of nuclear in disasters. Dave Lochbaum, the Nuclear Safety Project director at the Union of Concerned Scientists, said that the incidents underscore the inadequacy of safety in U.S. plants, many of which are designed to cope with power outages for only four hours. Dozens of plants in the U.S. don't comply with fire safety regulations, which could compromise back-up systems. At Fukushima, back-up generators to power the cooling pumps were apparently knocked out by the tsunami that followed the earthquake and back-up batteries also failed to work, according to reports.

"Reactor emergency plans in the U.S. rely on the assumption that a reactor accident would be the only demand on emergency response resources. The accident in Japan is just the most recent reminder of the need to revisit emergency plans to ensure that people get the help they need even when disasters overlap," he wrote.

Supporters of nuclear power say that the crisis in Japan is being blown out of proportion in relation to the larger emergency in dealing with the aftereffects of the earthquake, where as many as 10,000 people could be killed and the economy severely hurt. Whether nuclear power plants should spend the money to enact more stringent safety requirements, such as impact from earthquakes the size of Japan's, is a question that society has to answer, said MIT's Golay.

"We have a pot of resources for public protection and we have to decide how to use them. We're talking about very expensive remedies and it's a social choice," he said. "If we do that, we're not going to protect ourselves against other things or we could spend the resources elsewhere like better schools, for instance."

Support for nuclear power appeared to have been building among the public in the U.S. over the past few years because nuclear plants offer emissions-free electricity generation at large scale. Some new plant designs use so-called passive systems, such as gravity, to power cooling systems, avoiding the problem of power failures.

"New plants are on an order of magnitude--ten times--safer than the existing fleet and they did this by improved designs," said Kadak. "If people worry about global climate change, then they cannot take nuclear off the table."

The Department of Energy has promoted the development of modular, relatively small-scale reactors as a way to more quickly bring nuclear power online and as a technology U.S. companies could sell abroad. In a press briefing yesterday, the White House press secretary said President Obama continues to support nuclear power plants and that U.S. plants had been built to withstand strong storms and earthquakes, The Hill reported. Federal government loan guarantees to build multibillion nuclear power plants is considered a key piece to any future energy legislation.

Whether and how much the so-called nuclear renaissance will be slowed by the events in Japan remains to be seen, said MIT's Golay. "What we have seen in the past is when shocks occur, there's (stalling) for five years and if everything goes well, society becomes more tolerant," he said.