Tokyo Electric Power Company Holdings Inc. also announced that based on image analysis, a hole measuring 2 meters in diameter has been found on a metal grating beneath the pressure vessel inside the containment vessel and a portion of the grating was distorted.
According to TEPCO, the extremely high radiation level was found near the entrance area in the space just below the pressure vessel. The previously highest radiation level monitored in the interior of the reactor was 73 sieverts per hour.
The hole could have been caused by nuclear fuel that penetrated the reactor vessel as it overheated and melted due to the loss of reactor cooling functions in the days after a powerful earthquake and tsunami on March 11, 2011 hit northeastern Japan.
According to the image analysis, about 1 square meter of the grating was missing.
The plant operator plans to deploy a robot at the bottom of the reactor containment vessel, which houses the reactor pressure vessel, to check the conditions there.
The analysis follows TEPCO’s discovery Monday of a black mass deposited on the grating directly beneath the pressure vessel, possibly melted fuel after the unit suffered a meltdown along with two other Fukushima Daiichi reactors.