The Japanese government now estimates that total costs - including compensation, decommissioning and decontamination - could reach 20 trillion yen (USD 178 billion) or even more, public broadcaster NHK reported today.
The figure, which it obtained from unidentified government sources, is nearly double the previous estimate of 11 trillion yen made three years ago.
An official at the economy, trade and industry ministry, which oversees the nuclear sector, could not confirm the report.
"Discussions will continue into next year," the official said.
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A massive undersea quake on March 11, 2011, sent a giant tsunami barrelling into Japan's northeastern coast, leaving more than 18,500 people dead or missing, and sending three reactors into meltdown at the Fukushima nuclear plant.
It was Japan's worst postwar disaster and the most serious nuclear accident since Chernobyl in 1986.
The cost of decommissioning Fukushima, to be borne by TEPCO, will likely quadruple from the earlier estimate to eight trillion yen while decommissioning and compensation costs will also rise by trillions of yen, NHK said.
It also has to pay compensation to residents, while the government will incur part of the costs for decontamination and building storage for contaminated debris.