Tokyo Electric Power Co. is facing sharp criticism both for its delay in resolving the loss of cooling functions at its Fukushima No. 1 nuclear power plant and for the lax practices that led to the scare.
The blackout cut power to cooling equipment at several nuclear fuel storage pools and had the potential to become catastrophic. With the cooling functions shut down, the temperature of the fuel rods in the pools could have risen enough to evaporate the cooling water, possibly leading to a meltdown of the fuel.
"This clearly shows that the plant has not yet been stabilized," said Shiro Izawa, who on March 10 became mayor of Futaba, one of the municipalities that hosts the plant.
TEPCO officials apparently were not seriously concerned by the possibility of a meltdown of fuel rods in the pools.
Though the company has taken measures to provide several backup electricity sources for the cooling of the reactors at the Fukushima No. 1 plant, it has not implemented such measures for the cooling equipment used in the storage pools. One reason is that utility officials apparently believe the rise in water temperatures in the event of a temporary blackout would be slower than that for reactors, meaning they will likely have more time to deal with a loss of power to the storage pool cooling equipment.
But at a March 19 news conference, Shunichi Tanaka, chairman of the Nuclear Regulation Authority, said TEPCO needed to take measures to ensure backup power sources for the cooling equipment.
At the same time, Tanaka indicated there was a possibility of similar blackouts occurring in the future because the high radiation levels at the plant made it difficult to conduct reinforcement work.
"What will be important is to implement measures to prevent fatal events from happening," he said.
Cooling functions at the No. 1 and No. 4 reactor storage pools were restored between noon and the evening of March 19, but resumption of cooling at the No. 3 reactor storage pool only came at about 10:40 p.m. Cooling of the common storage pool, which contains 6,377 fuel assemblies, the most of any storage pool at the plant, resumed at about 12:10 a.m. on March 20, some 29 hours after the blackout occurred.
TEPCO officials believe the blackout, the longest since the March 2011 accident at the plant, was likely caused by a malfunctioning temporary switchboard. The switchboard is connected to the cooling systems for the No. 3 and No. 4 reactor storage pools and the cooling equipment for the common pool.
The malfunction also affected the switchboards used for the cooling equipment for the No. 1 reactor pool and a separate cooling system for the No. 4 reactor pool.
TEPCO officials said March 20 they found a charred terminal on the temporary switchboard believed to be the cause of the blackout. While a further investigation will be conducted to determine what caused the burning, officials suspect an overcurrent occurred.
To restore cooling functions, TEPCO had to bypass the temporary switchboard to route electricity to various equipment.
Because the switchboard is situated outside, its usage environment is less stable than ones used indoors. For that reason, TEPCO officials had planned to convert some of them to indoor switchboards by the end of March.
But such temporary equipment is still in use at the plant for other functions beyond the supply of electric power.
Local government leaders, meanwhile, criticized TEPCO for the slow manner in which it dealt with the blackout.
Katsunobu Sakurai, the mayor of Minami-Soma, located north of the plant, called TEPCO officials to the municipal government building and asked for an investigation into the cause of the incident, the rapid resumption of electricity and a speedy transmission of information.
"There were many people who were shaken by the news they heard," Sakurai told utility officials. "There is the possibility that some people who thought of returning in the new fiscal year will not be able to do so."
The Fukushima prefectural government also submitted a request to TEPCO to conduct a thorough investigation, restore electricity, diversify power source equipment and provide information on problems at the plant.
The longest previous blackout at the plant was about 10 hours. There have also been planned blackouts in the past when electricity was temporarily shut down to inspect switchboards.
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