Mark Willacy. Fukushima clean-up chief still hunting for 600 tonnes of melted radioactive fuel. ABC, May 24, 2016, http://www.abc.net.au/news/2016-05-24/fukushima-operator-reveals-600-tonnes-melted-during-the-disaster/7396362
In an exclusive interview with Foreign Correspondent, the Tokyo Electric Power Company's chief of decommissioning at Fukushima, Naohiro Masuda, said the company hoped to pinpoint the position of the fuel and begin removing it from 2021.
But he admitted the technology needed to remove the fuel has to be invented.
"Once we can find out the condition of the melted fuel and identify its location, I believe we can develop the necessary tools to retrieve it," Mr Masuda said....In Reactor 1, all of the fuel has melted down from inside the pressure vessel," Mr Masuda said.
"In reactors 2 and 3, about 30 per cent to 50 per cent remains in the pressure vessel and the rest has melted down. But unfortunately, we don't know exactly where [the fuel] is...
..."It's estimated that approximately 200 tonnes of debris lies within each unit," said TEPCO's Naohiro Masuda. "So in total, about 600 tonnes of melted debris fuel and a mixture of concrete and other metals are likely to be there."
Where Might the Missing Fuel Be Located?
Although some of it may be in the atmosphere and in the Pacific Ocean, much of the fuel from reactor unit 1 may be located under the plant in the underground river, as illustrated by this diagram that was originally posted by the Swiss Embassy in Japan: