Collapsed scaffolding in No.3 reactor

June 20, 2017

Fukushima robot reveals collapsed scaffolding in nuclear reactor

http://www.asahi.com/ajw/articles/AJ201707200046.html

By KOHEI TOMIDA/ Staff Writer

New images of inside the Fukushima No. 1 nuclear power plant taken by a swimming robot reveal previously unseen damage from the meltdown that followed the March 2011 earthquake and tsunami.

The images show the collapsed state of metal scaffolding that had been installed for maintenance work beneath a pressure vessel that sits within a containment vessel inside the plant’s No. 3 reactor.

It is highly likely that melted nuclear fuel fell through the pressure vessel and weakened the scaffolding, leading to its collapse.

Almost all of the nuclear fuel in the No. 3 reactor likely melted and dropped from the pressure vessel and accumulated at the bottom of the containment vessel, according to analysis by Tokyo Electric Power Co., the crippled plant’s operator.

Coolant water in the containment vessel is about 6.4 meters deep. TEPCO sent the robot, specially designed for underwater probes, inside the No. 3 reactor on July 19 and released the pictures that day.

The camera-equipped robot captured images of the collapsed scaffolding after moving forward to the opening of a tube-shaped concrete object that supports the pressure vessel.

Metal parts to support devices at the bottom of the pressure vessel had also vanished.

TEPCO plans to collect images of the melted nuclear fuel that is believed to have accumulated at the bottom of the containment vessel on July 21.

In light of damage to the scaffolding and other parts that was identified by the July 19 survey, TEPCO planned to examine the route for the robot to enter the vessel on July 20.

The investigations follow robot probes in the plant’s No. 1 and No. 2 reactors, which were conducted from January to March.

TEPCO and the government plan to decide how to remove the nuclear fuel as early as this summer in accordance with results of the robot probes on all three reactors.