The Nuclear Regulation Authority released a video on Thursday of an on-site investigation of the No. 3 reactor building at Tokyo Electric Power Company Holdings Inc.'s Fukushima No. 1 nuclear power plant.
Of reactors No. 1, 2 and 3, which were all hit by nuclear meltdown, the buildings of reactors No. 1 and 3 were destroyed by hydrogen explosions. Radiation levels in the upper part of the No. 3 reactor building were extremely high at specific points compared with those in reactor buildings No. 1 and 2. The location of the radioactive source at the No. 3 reactor is unknown.
The NRA's investigation was conducted on Dec. 12 to identify the source of radiation and determine the damage done by the hydrogen explosion.
Images of the third floor of the building, where equipment to control the fuel storage pool was located, showed severe damage, including broken beams that once supported the building and countless pieces of scattered concrete. The ceiling was bent downward over a wide area. "It can be assumed that strong pressure from the explosion was applied from at least the fourth floor and also from above the building," a NRA official said.
Radiation levels inside the building are still high, with 150 millisieverts (mSv) measured on the surface of pipes on the second floor and 50 mSv on the third floor. The source of the radiation could not be identified.
The NRA aims to compile a report by the end of 2020 and will also examine the leakage routes of radioactive substances and the operation status of cooling equipment for nuclear reactors.
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