The cooling system at the No. 4 unit spent fuel pool at the crippled Fukushima Daiichi nuclear power plant temporarily halted Tuesday after an alert over electrical equipment was issued, plant operator Tokyo Electric Power Co. said.
The operation to remove fuel from the spent fuel pool was also suspended. TEPCO said workers damaged a cable during drilling work taking place near the electrical equipment.
According to TEPCO, an alert over the electrical equipment at the site was issued at 9:40 a.m. and the cooling system for the No. 4 spent fuel pool stopped about five minutes later.
While the temperature of the water inside the pool rose to 13.1 C from 13 C while the cooling was suspended, TEPCO said it was able to restart the system by 2:16 p.m.
The damaged cable also caused a fire but it has been extinguished.
Major facilities other than the No. 4 pool cooling system have not shown any abnormalities.
TEPCO started the delicate work to remove over 1,000 fuel assemblies from the spent fuel pool inside the damaged No. 4 reactor building in November.
The Nos. 1 to 3 reactors, all in operation at the time of the earthquake in March 2011, experienced core meltdowns.
The No. 4 reactor, offline for periodic maintenance work, had all of its fuel stored in the spent fuel pool and avoided a meltdown, but concerns have remained over the continued storage of the large volume of fuel in the building, which was weakened by a hydrogen explosion.