Work to prevent rodents from causing another blackout at the stricken Fukushima No. 1 nuclear plant accidentally shut down the cooling system for a spent fuel storage pool on April 5, the plant's operator said.
The cooling system didn’t work for about three hours, leading to a slight rise in the temperature at the fuel storage pool in the No. 3 reactor building from 15.1 degrees to 15.2 degrees.
Radiation monitoring devices around the No. 3 reactor building did not show any abnormal figures, Tokyo Electric Power Co. said.
“We are sorry for causing the trouble. We will be more careful so that we will not make mistakes,” TEPCO spokesman Masayuki Ono said.
On March 18, a rat entered a container of a temporary switchboard at the plant, causing a large-scale blackout that halted cooling systems for fuel storage pools at the No. 1, No. 3 and No. 4 reactor buildings. Power was restored after two days.
To prevent rats and other small animals from entering the container again, workers installed wire mesh over cracks and openings on April 5. When a worker tried to put the mesh in place, a wire from it touched the terminal of the switchboard, leading to the stoppage of the cooling system, TEPCO said.
To prevent mishaps from affecting the system, TEPCO needed to shut down the cooling operations while the work was under way to install the mesh wire.
But company officials acknowleged they lacked cautiousness by deciding to keep the system online during the work on April 5.
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