A rat apparently gnawed on a switchboard or its wiring, causing the 30-hour power cutoff for the spent-fuel pool cooling systems at the triple-meltdown-hit Fukushima No. 1 nuclear plant that led to renewed fallout fears, Tokyo Electric Power Co. indicated Wednesday.
Tepco said it found the burnt carcass of what appeared to be a rat near the makeshift switchboard as well as burn marks on the equipment, although it has yet to determine the exact cause of the power outage.
The switchboard runs the cooling systems of the spent-fuel pools of reactors 3 and 4 as well as a common pool located inside another building at the site that contains 6,377 nuclear fuel assemblies.
Tepco said it had not taken any steps to prevent wildlife, such as rodents, from getting at the switchboard and said it is continuing to investigate other factors that may have caused the power outage, which was apparently resolved minutes after midnight Tuesday.
The makeshift switchboard was located on the back of a truck that had been parked outside since May 2011. Tepco was planning to stop using the equipment and switch to a new permanent switchboard by the end of this month.
The cooling system for reactor 1 has a separate electrical system from the makeshift power switchboard, but at the time of the power outage it was connected to the makeshift switchboard due to ongoing multiple tasks and was affected, the utility said.
Tepco restarted all nine power outage-hit facilities, including an installation to remove radioactive substances from water used to cool the crippled reactors, by midnight Tuesday after electricity went out a day earlier.
On Wednesday, the water temperature stood at 31.8 degrees in the common pool that stores the 6,377 fuel assemblies, 31 degrees in the reactor 4 spent-fuel pool and 17 degrees in both the reactors 1 and 3 fuel pools.
Those temperatures are between 1 and 6.3 degrees higher than the levels before the power outage.
Tepco spokesman Masayuki Ono said, “It will take several days for the temperatures to get back to normal.”
The latest trouble occurred more than two years after the plant was ravaged by the tsunami from the March 11, 2011, Great East Japan Earthquake, as well as possibly by the temblor itself. Reactors 1-3 suffered core meltdowns after the disaster struck, as well as hydrogen explosions, which destroyed the building housing reactor 4 and left its spent-fuel pool exposed.