It is highly likely that 70-100% percent of the fuel in the unit 2 reactor at Japan's Fukushima Daiichi nuclear power plant melted in the wake of the 2011 nuclear disaster, a group of researchers reported on 26 September.

The group, which includes researchers from Nagoya University, arrived at the conclusion after inspecting the interior using a fluoroscopic device, which utilizes elementary particles called muons. Tokyo Electric Power Co (Tepco) had earlier said some of the fuel remained inside the reactor. The group, led by Nagoya University researchers, has been investigating the reactor since last year.

Previously they used the same technique to look inside the unit 1 reactor and again detected few signs of nuclear fuel remaining in the core. The location of the nuclear fuel will have a significant impact on which process is used to remove it from the damaged reactors, the most difficult step of the decommissioning work. The Japanese government and Tepco plan to scan unit 2 reactor again using a different device.

Photo: Muon detection equipment being installed into Fukushima Daiichi unit 1 in February (Credit: Tepco)