When radiation levels surged following a fire at Unit 4 and a rising cloud of radioactive vapor from unit 3, officials deemed it too risky for the plant workers to continue their critical work of pumping sea water on the damaged reactors and fuel ponds.
"The workers cannot carry out even minimal work at the plant now," Chief Cabinet Secretary Yukio Edano told the Associated Press. "Because of the radiation risk we are on standby."
Radiation levels were as high as 10 millisieverts per hour today, the equivalent of getting a CT scan for every hour of exposure. Radiation levels have since dropped and the plant workers are planning to return to work, officials said.
The Japanese government has actually amended its national safety standard on how much radiation workers can be exposed to so that workers can return to the plant. The limit is now 250 millisieverts, 2.5 times the previous limit.
In the aftermath of the 9.0 magnitude earthquake and tsunami, the growing fear of a nuclear meltdown has spread throughout Japan.
Emperor Akihito, a figure deeply respected in Japan, spoke for the first time since the Mar. 11 earthquake that has left at least 4,340 people dead. He tried to ease worries about the country's nuclear crisis.
"With the help of those involved I hope things will not get worse," Akihito, 77, said.
He offered his condolences to a grieving nation where at least 9,083 people are still missing and 434,00 are homeless.
"It is important that each of us shares the difficult days that lie ahead," Akihito said. "I pray that we will all take care of each other and overcome this tragedy."
In another sign of escalating nuclear danger, Cabinet Secretary Edano acknowledged that the containment vessels of some of the reactors are likely damaged. The Japan Atomic Industrial Forum confirmed damage to Units 2 and 3.
The last step in a nuclear meltdown is the breaching of the containment vessels. The fact that at least two containment vessels are damaged makes nuclear experts nervous.
"We have cracks now, cracks in the containment vessels...and if those cracks grow or if there's an explosion, we're talking a full blown Chernobyl, something beyond Chernobyl," Kaku said.
Some scientists believe that the accident level at the troubled plant should be escalated to a level 6, just one level lower than Chernobyl and two levels higher than the accident at Three Mile Island.
"I think the last ace in the hole is the Japanese Air Force, the military at some point may have to take over, may have to bury these reactors in concrete just like we did at Chernobyl, sandbagging the reactor with 5,000 tons of concrete, boric acid and sand," Kaku said.
Earlier today, government officials called off a plan for helicopters to dump seawater on the troubled reactors because of the heightened radiation levels.
The Japanese government has asked for the United States' help in the crisis.
Already, seven additional experts from the U.S. Nuclear Regulatory Commission arrived in Japan today.
The United States government may be sending in a special nuclear team, made up of hundreds of U.S. military personnel trained specifically for nuclear emergencies. They would be help respond to the disaster and offer aid to the local population if they suffered decontamination.