The 9.0-magnitude earthquake and tsunami that struck Japan late last week caused a human and environmental tragedy. It also set off a nuclear crisis that could have more serious consequences than the Chernobyl nuclear accident in Ukraine 25 years ago--unless Japanese scientists and engineers can prevent a nuclear meltdown.
The crisis began when the earthquake and tsunami knocked out the electricity that powers the cooling system in reactors at the Fukushima Daiichi nuclear-power complex. Since then, explosions at three of the six nuclear reactors at the plant and a fire at another have further damaged the cooling and containment systems.
Scientists have detected cesium-137 and iodine-131--two highly radioactive isotopes--outside the plant, a clear signal that two or more of the reactor cores are seriously damaged and at least partially melted down, according to U.S. nuclear experts. Officials in Japan are flooding the reactors with seawater in a desperate attempt to keep the cores from overheating and prevent further releases of radiation.
Since the nuclear crisis first began following the earthquake and tsunami, the Japanese government has gradually increased the evacuation zone around the nuclear plant, from two miles to six miles to twelve miles. Prime Minister Naoto Kan later urged the Japanese people to remain calm and advised anyone living with 18 miles of the nuclear plant to stay indoors.
Meanwhile, Pentagon officials said on Sunday that helicopters flying 60 miles from the nuclear plant detected small amounts of radioactive material, which shows a circle of environmental contamination that is spreading far beyond the evacuation zone.
If engineers succeed in cooling the nuclear reactor cores and preventing additional radiation leaks, the damage may be restricted to the few plant workers who are already being treated for radiation sickness.
If they fail, and the cores overheat and melt through the structure that is meant to contain them, the consequences may include an untold number of cancer deaths, billions of dollars in cleanup costs, and an environmental disaster that leaves the region around the nuclear plant uninhabitable for decades.
The real worst-case scenario, the one that has officials and ordinary citizens in Japan and around the world on edge as the crisis unfolds, depends on weather. If a meltdown occurs, releasing massive amounts of radiation, and the wind blows south across the island of Honshu, the tragedy could be unprecedented in the history of the nuclear industry. Honshu, Japan's largest island, is home to 103 million people, including the populations of Tokyo and Osaka-Kyoto, according to the 2005 census.
The nuclear reactors are supposedly built to withstand nearly any kind of natural disaster, but they're not. Part of the problem, according to some nuclear experts, is that the reactors in Japan are built to withstand "most likely" rather than "worst-case" seismic events.
The fault is not news to Japanese officials, who have known for at least three years that the country's nuclear reactors might not withstand a major earthquake.
In July 2007, an earthquake led to a near disaster at the Kashiwazaki-Kariwa Nuclear Plant in western Japan. Following that event, inspectors from the International Atomic Energy Agency determined that a 6.6-magnitude earthquake "significantly exceeded the level of the seismic input taken into account in the design of the plant." The design of the reactors at that plant is the same as the reactors at the Fukushima Daiichi nuclear plant, which were damaged by the recent earthquake and tsunami and are now threatening to release deadly radiation into highly populated areas.
U.S. Sen. Joe Lieberman, chair of the Senate Homeland Security and Governmental Affairs Committee and a big supporter of expanding U.S. nuclear energy capacity, said on Sunday that the United States should "put the brakes on" building new nuclear reactors until we fully understand what happened in Japan. Lieberman also noted that there are 104 nuclear power plants in the United States, and that 23 of them are based on designs similar to the reactors in Japan that are now at risk of melting down and are causing global concern.
Updated March 14, after scientists upgraded the earthquake from magnitude 8.9 to 9.0