THE ASAHI SHIMBUN
April 5, 2023 at 17:03 JST
Tokyo Electric Power Co. plans to re-evaluate the ability of a pedestal inside the No. 1 reactor at its crippled Fukushima No. 1 nuclear power plant to withstand a major earthquake after a robotic probe confirmed that it had been heavily damaged.
The 8.5-meter-tall cylindrical pedestal, made of concrete, is a key piece of equipment that supports the reactor’s 440-ton pressure vessel. Its wall is about 1.2 meters thick.
The utility on April 4 released an approximately five-minute video taken by the robot last week, which showed that steel reinforcing bars had been exposed along the inner side of the pedestal’s wall for about 1 meter from its bottom and for about half its inner circumference.
TEPCO believes that concrete melted off in the lower part of the pedestal when molten nuclear fuel poured through the bottom of the pressure vessel. It suspects that the inner side of the pedestal’s wall could have sustained similar damage all around.
Nuclear fuel melted inside three of the four reactors at the Fukushima No. 1 plant when the Great East Japan Earthquake and tsunami struck in March 2011. Damage to the No. 1 reactor is believed to be the most severe among the three reactors.
TEPCO plans to estimate the extent of the damage based on the results of the robotic study and re-evaluate the equipment’s quake resistance, officials said.
The robotic study found debris, apparently melted nuclear fuel, above exposed rebars. Concrete remains in areas of the pedestal that are higher than the debris.
A previous robotic study last year had found melted concrete and exposed rebars on the outer side of the pedestal’s wall.
TEPCO originally planned to shoot video images all around the inner areas of the pedestal during the latest inspection.
But the probe stopped moving after covering about half of the inner circumference. Its cable apparently got snagged on equipment or other objects.
An estimate conducted in fiscal 2016 by the International Research Institute for Nuclear Decommissioning, which comprises electric utilities and nuclear reactor manufacturers, showed that quake resistance will not be compromised even if about one-fourth of the pedestal, as well as parts of the inner side of other sections, was damaged.
The robot shot video images of areas directly beneath the No. 1 reactor's pressure vessel on March 28-31. The video, which runs for about 39 hours in total, will be shown at a TEPCO facility.
(This article was written by Keitaro Fukuchi and Ryo Sasaki.)
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Layers of debris confirmed in an area outside the pedestal for the No. 1 reactor’s pressure vessel at the Fukushima No. 1 nuclear power plant (Provided by the International Research Institute for Nuclear Decommissioning)
