The Yomiuri Shimbun
A robot has detected highly dangerous levels of radiation in the Fukushima No. 1 nuclear power plant's No. 3 reactor building, it has been learned, indicating further safety measures will be needed before workers can enter the structure.
According to plant operator Tokyo Electric Power Co., the remote-controlled PackBot robot on Tuesday found radiation levels in the northwestern section of the building of 49 to 120 millisieverts per hour, which would pose a threat to human workers.
Time must be spent, therefore, removing or sealing up the radiation-contaminated debris in the building, before TEPCO starts work to stabilize the damaged reactors.
When similar measurements were conducted around doors in the southern section of the building on April 17, the radiation levels were 28 to 57 millisieverts per hour.
Tuesday's measurements were conducted because most of the northwestern section had not yet been examined.
Images taken by the robot showed that debris was scattered on the floor and that the door leading to the outside was standing open.
"Until around June, we'll make it our priority to remove debris with robots. We'll then check how radiation levels change," a TEPCO employee said. The company currently has no plans to send workers into the No. 3 reactor building, the employee said.
When the PackBot examined the power plant's No. 1 reactor building in April, it found radiation levels had reached 1,000 millisieverts per hour at some pumps. Levels at the other pumps were 10 to 49 millisieverts per hour.
TEPCO therefore determined it was safe for workers to enter the building and has already finished removing radioactive substances from the building's air.
Water leaks from No. 1 reactor
Meanwhile, TEPCO has announced that water has been leaking through small openings in the bottom of the No. 1 reactor's pressure vessel.
Combined, the openings would be equivalent to a hole several centimeters in diameter, and according to TEPCO, were made when melted nuclear fuel damaged the bottom.
The melted fuel likely has accumulated in the bottom of the vessel. TEPCO has admitted the situation is a meltdown, in which melted nuclear fuel cannot maintain its shape and drops down to lower parts of a reactor core.
TEPCO had previously said fuel was just partially damaged.
As the temperature in the pressure vessel remains stable at 100 C to 120 C, the situation is unlikely to get worse, TEPCO said.
However, it is highly likely that water also has been leaking from the containment vessel, which envelops the pressure vessel. This has affected TEPCO's ongoing water entombment operations, in which it is pouring water into the containment vessel to cool the pressure vessel.
(May. 14, 2011)