TOKYO (AP) — This week’s power outage at Japan’s tsunami-crippled nuclear plant may have been caused by a rat.

Masayuki Ono, spokesman for Tokyo Electric Power Co., the utility that runs the Fukushima Dai-ichi plant, says a 15-centimeter (6-inch) rat was found dead Wednesday near a switchboard. He says the rat may be linked to the power failure, but that more investigation is needed to be sure.

The carcass of a small animal lies inside a temporary electric switchboard at the Fukushima nuclear plant. Pic: AP.

Cooling systems at the plant for four storage pools for nuclear fuel were knocked out Monday. Power was restored early Wednesday at all nine affected facilities.

The power outage was a reminder that the world’s worst nuclear disaster since Chernobyl is far from resolved. Tsunami-damaged backup generators set off the March 2011 disaster. Decommissioning the Fukushima reactors is expected to take decades.