level at Fukushima reactor highest since 2011 disaster
The radiation level inside the containment vessel of the No. 2
reactor at the crippled Fukushima Daiichi nuclear complex stood at
530 sieverts per hour at a maximum, the highest since the 2011
disaster, the plant operator said Thursday.
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.
Images captured using a camera attached to a telescopic arm on
Monday also showed part of the grating has gone. A further analysis
of the images found a 2-meter hole in an area beyond the missing
section on the structure.
If the deposits are confirmed as fuel debris, it would be the
first time the utility has found any at the three units that suffered
Following one of the world's worst nuclear disasters since the
1986 Chernobyl catastrophe, the No. 1 to 3 reactors suffered fuel
Portions of the fuel in the reactors are believed to have melted
through the pressure vessels and accumulated at the bottom of the
The actual condition of the melted fuel has remained unknown due
to high radiation levels. (Feb. 2)