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.