The clean-up after the Fukushima nuclear disaster could cost five times more than estimated, figures have revealed, as Tokyo Electric Power said on Wednesday that steam had been seen again in a reactor building.

It is the third time steam has been observed in the battered structure over the last week.

The government-backed National Institute of Advanced Industrial Science and Technology said decontamination work in Fukushima prefecture will cost up to 5.81 trillion yen ($58 billion), far more than the 1 trillion yen the government has so far allocated.

The institute, in a report released Tuesday, said the costs - including for transportation and storage of radiation-contaminated soil over a large area - would be in a range between 3.13 trillion yen and 5.81 trillion yen.

‘We hope the study will be helpful in drafting plans for decontamination of forests and farmland, as well as plans for residents to return to their homes,