23 Mars 2013
March 22, 2013
The operator of the crippled Fukushima No. 1 Nuclear Power Plant suspects that the power outage that knocked out the plant's cooling systems for spent fuel pools was likely caused by a short circuit blamed on a small animal, revealing the utility's insufficient measures against those creatures.
A Tokyo Electric Power Co. (TEPCO) investigation found that a short circuit in a makeshift power switchboard -- which was installed two months after the March 2011 outbreak of the Fukushima nuclear disaster as part of a temporarily outdoor facility -- was likely caused by a small animal. The switchboard had no backup power sources.
It was the plant's first major blackout that affected multiple facilities for longer than 24 hours since the onset of the nuclear crisis, sending shivers throughout the country. The switchboard is connected to the cooling systems for the spent fuel pools of the No. 3 and No. 4 reactors as well as a shared pool, according to TEPCO. The malfunction of the switchboard is suspected to have further affected other equipment connected to it by cables.
The destroyed switchboard was one of four brought in by trailer, and was the last one in operation as TEPCO worked to replace the temporary outdoor switchboards with those inside reactor buildings. The work was scheduled to be completed by the end of the current fiscal year, or later this month.
A shutdown of the cooling systems for spent fuel pools causes fuel temperatures to rise, evaporating coolant water and eventually exposing fuel to bring about meltdowns. While multiple power sources are secured for the cooling systems of nuclear reactors, there were no reserve power sources for the spent fuel pools.
"It takes time for temperatures to rise in spent fuel pools even if their cooling systems are down. There is no need to take the same emergency countermeasures as those for nuclear reactors," TEPCO spokesman Masayuki Ono said.
The blackout also revealed TEPCO's lack of measures against small animals, such as the use of rodent deterrents and other medical agents. Because the switchboard's container has a half-open door to lead in cables, "it leaves the system vulnerable" to place the switchboard outdoors compared to inside the highly-sealable plant buildings, said TEPCO officials.
March 21, 2013(Mainichi Japan)