The removal of damaged fuel debris from Units 1, 2 and 3 at the Fukushima-Daiichi nuclear power station in Japan remains a key task in the decontamination and decommissioning (D&D) process, but “much more detail is needed from inside” the reactor cores, two webinars about the March 2011 accident have been told.

Hajimu Yamana, president of the Nuclear Damage Compensation and Decommissioning Facilitation Corporation of Japan (NDF), said retrieval of the fuel debris – known as corium – is the “biggest challenge” at the site in northern Japan because of the very harsh radiation environment.

He said: “We need to design a method using large-scale remote equipment and that is unprecedented. What is happening inside of the reactors is not fully understood and we need to secure the safety of workers and environment.”

Asked about the ultimate disposal of the fuel debris, Mr Yamana said it is “too early to say”.