A government study released Oct 25 found decommissioning the Fukushima Dai-ichi plant had already cost 80 billion yen ($770 million) over the last three years.
The plant suffered multiple reactor meltdowns due to damage from the March 2011 earthquake and tsunami.
The ministry overseeing nuclear power said the decommissioning costs will continue at several hundreds of billions of yen (billions of dollars) a year.
Tokyo Electric Power Co., has said decommissioning will take several decades.
Japan has been struggling to clean up parts of the no-go zone to put the worst nuclear catastrophe since Chornobyl behind it.