As of 14:00 local time (05:00 GMT) on Friday, the temperature of water inside the cooling pool at reactor 3 was 15.1C, well below the safety limit of 65C, Tepco said.

BBC: Fukushima nuclear plant: Cooling system power restored

Louis, high temperatures prompted city officials to open eight cooling centers and extend pool hours, steps similar to those taken by many other municipalities, including ones more than 1, 000 miles away in the Washington area.

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Restarting cooling to the spent fuel pool at reactor 4 had been of particular urgency for Tepco as it had the highest number of fuel assemblies stored there, Kyodo news agency reported.

BBC: Power at Fukushima nuclear fuel ponds restored

This is a very difficult situation, and there will be a lot of work continuing as we go forward to deal with continuing to cool the reactors and to provide cooling to the spent fuel pool.

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The IAEA statement was released hours after Tepco temporarily shut down the cooling system in the second unit's spent fuel pool following the discovery of dead rodents near a transformer.

BBC: IAEA calls for improvements at Japan's Fukushima plant