TOKYO // A rat may have caused a power cut that knocked out cooling systems at Japan's tsunami-wrecked Fukushima nuclear plant, the operator said yesterday.
Equipment keeping spent nuclear fuel at a safe temperature in four different pools was out for up to 29 hours from Monday, with Tokyo Electric Power Company (Tepco) admitting its recovery work was sometimes less than perfect.
The incident was a reminder of the precarious state of the plant two years after the tsunami, which sparked meltdowns in three reactors, spewing radiation over land and sea and forcing tens of thousands from their homes.
"We suspect a small animal may have caused a short-circuit in a switchboard" leading to the power cut and disabling cooling systems for used fuel pools, a spokesman for Tepco said.
"We cannot be sure exactly what it was, but can say what we saw at the scene was the body of a dead animal below the switchboard," he said.
"In our investigation we will concentrate on getting assurances that it was definitely this animal that caused the short-circuit."
A photograph Tepco released showed a creature that appeared to be a rat, with a body around 15 centimetres long.
The switchboard was a temporary one on the back of a vehicle, which was due to be replaced by a permanent one, Tepco said, without specifying a time frame.
The crisis began Monday night when power was cut at a building that serves as the central command for work to contain the nuclear accident and dismantle the reactors.
By Tuesday afternoon some electricity had been restored, but it was not until 29 hours after the original power cut that the supply was normalised.
TEPCO and the government said in December 2011 that the crippled reactors were "in a state of cold shutdown" — a phrase carefully chosen, commentators said, to imply the normality of units that were so broken they would not easily fit classical descriptions.
Authorities insist they are getting on top of the problem and the reactors are not leaking significant amounts of radiation.
"Despite the fact it is now two years since the crisis began, TEPCO is still doing a very poor job," said Muneo Morokuzu, professor of nuclear regulation at Tokyo University.