TOKYO: Engineers at Japan’s crippled Fukushima nuclear plant partially succeeded Tuesday in restarting cooling systems after a power cut underlined its still-precarious state two years after a tsunami struck.
Equipment in pools used to keep used fuel cool — necessary to prevent any spontaneous nuclear reactions — lost their power supply at 7 pm (1000 GMT) on Monday, operator TEPCO said.
By late Tuesday two of the cooling systems were back up, reports said. One other was likely to be online later in the day, the company said earlier.
Even used nuclear fuel becomes dangerous if its temperature is allowed to rise uncontrollably to the point where a self-sustaining critical reaction begins, causing a meltdown.
TEPCO, which was previously criticised for not telling the public or press exactly what was happening at the atomic plant, said there was no imminent danger, although it admitted it does not know what caused the fault.
“Electricity has been cut to pools used to cool spent fuel at reactors 1, 3 and 4” as well as to the equipment used to treat contaminated discharge including radioactive caesium, TEPCO spokesman Kenichi Tanabe said earlier.
Power was restored to part of the equipment, with the cooling system for the fuel pool at reactor 1 having returned to full operation at 2:20 pm Tuesday, TEPCO said in a statement.
Kyodo news reported the cooling system on the fuel pool at reactor 4 was also working again. The system on the pool at reactor 3 will likely return to full operation Tuesday evening, the company said.
A separate cooling system for a common pool is expected to be back online at 8:00 am on Wednesday, ending the current problem, it said. The common pool contains more than 6,000 used fuel rods.
The incident has not so far affected the injection of cooling water to reactors 1, 2 and 3 themselves, Tanabe said. These suffered core meltdowns soon after the start of the March 2011 nuclear crisis.
The temperatures of all fuel pools remains well below the safety limit of 65 degrees Celsius (149 Fahrenheit), and had been rising by 0.3-0.4 degrees every hour, the TEPCO spokesman said.
TEPCO officials said there had been no major changes in the level of radioactivity at nearby monitoring spots. The meltdown of three of Fukushima’s six reactors occurred after an earthquake and ensuing huge tsunami on March 11, 2011, shut off the power supply and cooling system.