The power outage that affected the spent nuclear fuel pools at the Fukushima-Daiichi nuclear power plant earlier this week was apparently caused by a rat or rat-like animal, according to TEPCO officials quoted in news reports.
As of March 20, power had been fully restored to all fuel cooling pools at the facility.
The glitch knocked out the cooling system at four of Fukushima's nuclear pools, which contain thousands of used fuel rods.
Temperatures in the pools then began to rise gradually, and it took TEPCO more than 24 hours to get all the cooling systems back up and running.
The company says it found burn marks on a makeshift power switchboard, and has blamed a "rat-like animal" for short-circuiting it.
The cooling shutdown highlights just how vulnerable the shattered plant remains, two years after the nuclear meltdowns.
TEPCO released an image of the rodent carcass found near the damaged switchboard unit that caused led to the surprise outage. Burn marks were found on the switchboard, which was apparently short circuited by the rat.