Photo/Illutration Icicle-shaped objects that may be nuclear fuel debris photographed by a drone at the bottom of a reactor pressure vessel (Provided by Tokyo Electric Power Co.)

Icicle-shaped objects that may be melted nuclear fuel debris were captured in photos taken by a small drone directly under a damaged reactor pressure vessel at the Fukushima No. 1 nuclear power plant.

“Very useful information has been obtained,” a Tokyo Electric Power Co. official said at a news conference on March 18, when the images were released.

The survey was conducted on March 14 to study methods of removing the fuel debris.

Melted fuel rods at the No. 1 reactor are believed to have broken through the bottom of the pressure vessel after the tsunami on March 11, 2011, slammed into the nuclear plant and cut off power.

The drone and a snake-shaped robot with a wireless relay system were placed in the containment vessel and remotely operated from another building.

The images were taken directly below the pressure vessel, which is housed within the containment vessel.

According to TEPCO, the images show that the “control rod,” which suppresses the nuclear fission reaction, had fallen off, and an icicle-like object was attached to it.

A lumpy object hanging down from the top was also observed.

There is a strong possibility that the icicle-like and lumpy objects fell from the top of the pressure vessel, but the official said, “We cannot determine at this point” whether these objects are fuel debris or melted equipment.

“We would like to more carefully evaluate the images we have taken,” the official added.

From February 2022 to March 2023, a swimming robot was used in the No. 1 reactor to photograph the cooling water that accumulated at the bottom of the containment vessel.

The photos showed that the lower 1 meter of the inner wall of a concrete pedestal supporting the reactor had exposed rebar all the way around.

The latest drone survey checked further up the inner wall and confirmed there was still concrete there, TEPCO said.

The No. 1, No. 2 and No. 3 reactors at the plant melted down after the Great East Japan Earthquake and tsunami. The fuel debris in these three ruined reactors is estimated to weigh a total of 880 tons.

In the No. 1 reactor, 90 percent or more of the fuel debris is believed to have fallen from the pressure vessel.

(This article was written by Keitaro Fukuchi and Fumi Yada.)

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