Tokyo Electric Power Co. (9501.TO) said Tuesday it has resumed cooling the spent fuel pools of the Nos. 1, 3 and 4 reactors at the crippled Fukushima Daiichi nuclear power plant, a day after the key system was suspended due to a suspected problem with a power switchboard, Kyodo News reported.
Tokyo Electric Power Co. (9501.TO) said Tuesday it has resumed cooling the spent fuel pools of the Nos. 1, 3 and 4 reactors at the crippled Fukushima Daiichi nuclear power plant, a day after the key system was suspended due to a suspected problem with a power switchboard, Kyodo News reported.

The incident did not affect the injection of water into the Nos. 1, 2 and 3 reactors that suffered core meltdowns, but indicated that the situation remains vulnerable more than two years after the plant was ravaged by the quake-triggered tsunami on March 11, 2011 .

TEPCO spokesman Masayuki Ono told a press conference that the utility has yet to determine the cause of the incident.

Electricity went out at a total of nine facilities, including an installation to remove radioactive substances from water used to cool reactors and a cooling system for a common pool located inside another building at the site.

Mr. Ono said it was the first time such a large number of facilities, including important instruments, had suffered an electricity failure simultaneously since the plant was brought under control in December 2011.

TEPCO said the electricity instantaneously went out at the plant's accident response center at 6:57 p.m. Monday.

The cooling system for the Nos. 1 and 3 spent fuel pools was also put back online on Tuesday.

The temperature of the No. 4 spent fuel pool stood at 30 C at 4:30 p.m. , compared with 25 C at 4 p.m. a day earlier. TEPCO has set an upper limit of 65 C to secure safety during normal operations.

TEPCO said the cooling system of the common pool was restored shortly after midnight Tuesday, meaning the operation of all nine facilities has recovered. The pool stores a total of 6,377 fuel assemblies.

The company suspects a problem at a makeshift power switchboard caused the suspension of the cooling system. The equipment in question is the only remaining makeshift power switchboard at the plant, installed after the nuclear crisis, according to Mr. Ono.

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