Drone flies into damaged Fukushima nuclear reactor to exam molten fuel debris

TOKYO — A drone small enough to fit in one’s hand flew inside one of the damaged reactors at Japan’s Fukushima Daiichi nuclear power plant Wednesday in hopes it can examine some of the molten fuel debris in areas where earlier robots failed to reach.

Tokyo Electric Power Company Holdings also began releasing the fourth batch of the plant’s treated and diluted radioactive wastewater into the sea Wednesday. The government and TEPCO, the plant’s operator, say the water is safe and the process is being monitored by the International Atomic Energy Agency, but the discharges have faced strong opposition by fishing groups and a Chinese ban on Japanese seafood.

A magnitude 9.0 quake and tsunami in March 2011 destroyed the plant’s power supply and cooling systems, causing three reactors to melt down. The government and TEPCO plan to remove the massive amount of fatally radioactive melted nuclear fuel that remains inside each reactor — a daunting decommissioning process that’s been delayed for years and mired by technical hurdles and a lack of data.

To help on data, a fleet of four drones were set to fly one at a time into the hardest-hit No. 1 reactor’s primary containment vessel. TEPCO plans to probe a new area today.

TEPCO has sent a number of probes — including a crawling robot and an underwater vehicle — inside each reactor but was hindered by debris, high radiation and the inability to navigate through the rubble, though they were able to gather some data. In 2015, the first robot to go inside got stuck on a grate.

Wednesday’s drone flight comes after months of preparations that began in July at a nearby mock facility.