TOKYO -- Just four hours after the tsunami swept into the Fukushima nuclear power plant, Japan's leaders knew the damage was so severe the reactors could melt down, but they kept their knowledge secret for months. Five days into the crisis, then-Prime Minister Naoto Kan voiced his fears it could turn worse than Chernobyl.

The revelations were in documents released yesterday, almost a year after the disaster. The minutes of the government's crisis management meetings from March 11 -- the day the earthquake and tsunami struck -- until late December were not recorded and had to be reconstructed retroactively.

They illustrate the confusion, lack of information, delayed response and miscommunication among government, affected towns and plant officials, as some ministers expressed a sense that nobody was in charge when the plant conditions quickly deteriorated.

The minutes quoted an unidentified official explaining that the reactors' cooling functions were kept running only by batteries that would last only eight hours.

"If temperatures in the reactor cores keep rising beyond eight hours, there is a possibility of meltdown," the official said during the first meeting that started about four hours after the magnitude-9.0 earthquake and tsunami hit the Fukushima Dai-ichi plant March 11, setting off the crisis.

Apparently, the government tried to play down the severity of the damage. A spokesman for the Nuclear and Industrial Safety Agency was replaced after he let slip the possibility of a meltdown during a news conference March 12. The plant operator, Tokyo Electric Power Co., acknowledged a partial meltdown much later, in May.

According to minutes dated March 16, Kan said of possible meltdowns at Fukushima and the neighboring Dai-ni plant, "The amount of radiation that could be released from those reactors could be larger than Chernobyl."

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