A momentary voltage drop on Jan. 17 stopped the cooling equipment for storage pools containing spent fuel at the Fukushima No. 1 and No. 2 nuclear power plants, Tokyo Electric Power Co. officials said.
A momentary voltage drop on Jan. 17 stopped the cooling equipment for storage pools containing spent fuel at the Fukushima No. 1 and No. 2 nuclear power plants, Tokyo Electric Power Co. officials said.
While cooling equipment for the reactors of the two nuclear plants continued to operate, the stoppage showed that no backup system was in place to continue operations even with a momentary drop in voltage.
A malfunction in electricity transmission equipment in Tamura, Fukushima Prefecture, led to the momentary voltage drop over a wide area, but TEPCO officials said they did not immediately know the reason for the glitch.
TEPCO officials said the equipment was back in operation after about three hours. Eleven pieces of equipment stopped after the voltage drop, including those used to inject nitrogen to prevent a hydrogen explosion in the reactors. The nitrogen injection equipment resumed operations in about 50 minutes.
Although the cooling equipment for storage pools containing spent nuclear fuel at two reactors at the Fukushima No. 2 nuclear power plant shut down, TEPCO officials said there was no major increase in the water temperature of the pools nor any unusually high radiation readings in the vicinity.
TEPCO officials said all the equipment that stopped would not lead to a critical situation unless a considerable amount of time passed. For that reason, there was no system to automatically restart the equipment.
Because external power sources were available, the equipment was gradually restarted after TEPCO confirmed the condition of the equipment.
That was a far cry from what happened after the March 11 Great East Japan Earthquake, when not only all external power sources were lost at the Fukushima No. 1 nuclear power plant, but emergency diesel generators and batteries were also rendered inoperable by the tsunami.
The inability to adequately cool the reactor cores and storage pools led to the accident spiraling out of control.
After those natural disasters and accident, TEPCO installed or prepared alternative power sources to cool the reactors in case of emergencies. Firefighting vehicles have also been placed on high ground within plant grounds to pump water into the reactor cores in emergencies.
Because the momentary voltage drop did not lead to a power outage, there was no need to use such emergency power sources.
Batteries are installed in equipment such as computers to prevent serious incidents from a momentary voltage drop. But batteries are not used in other equipment if they are unlikely to cause problems if operations are temporarily stopped and later restarted.
One issue TEPCO officials will still have to deal with is the large number of temporary equipment now being used at the Fukushima No. 1 nuclear power plant. That is one reason it took as long as three hours to restart some of the equipment after the voltage drop.