Tokyo Electric Power Co. said Tuesday that the radiation level inside the reactor 2 at the Fukushima No. 1 power plant was at an extremely high level of 31.1 to 72.9 sieverts per hour, underscoring the existence of radioactive substances from the melted fuel inside the structure.
Tepco measured the radiation level by inserting a long dosimeter into the flask-shaped primary containment vessel, where fuel is thought to be accumulating at the bottom.
The highest radiation level was measured at about 4 meters from the bottom and about 1 meter from the vessel's interior wall.
Human beings could die within one month if exposed to 7 sieverts and within several days if exposed to 20 sieverts or more.
According to an industrial endoscope survey carried out Monday, Tepco found that the vessel was filled with water only 60 cm deep, lower than expected considering the amount of water injected into the reactor to keep the fuel cool.
The No. 2 reactor is one of the plant's three reactors that has suffered a meltdown, and its fuel is believed to have burned through the pressure vessel and accumulated in the outer primary container.