The operator Tokyo Electric Power Co said it now expects to finish treating the radiation-contaminated water at the Fukushima Daiichi nuclear plant by the end of May.
“We took the promise with Prime Minister [Shinzo Abe] very seriously but we cannot fulfill our commitment,” company president Naomi Hirose told Takayuki Ueda, commissioner of the Agency for Natural Resources and Energy.
When Abe visited the plant in September 2013, Hirose pledged that the operator would filter all the water kept in tanks by the end of March this year to reduce the amount of radioactive materials it contains.
“The problem of toxic water is the biggest source of concern for the local residents and we are extremely sorry to be unable to keep our word,” Hirose said.
The operation has been delayed due to a series of problems with its key water treatment facilities.
The plant suffered meltdowns at three of its six reactors after a tsunami swept through the complex in March 2011.
The operator continued to inject water into the three reactors to keep them cool. The amount of toxic water is believed to be increasing by about 350 tons each day.
Groundwater is also reportedly seeping into reactor buildings and mixing with contaminated water.
As of late December, the operator has built 990 storage tanks to contain such large amounts of toxic water, it said.