Four of the troubled Fukushima Dai-ichi plant's six reactor units have seen fires, explosions or partial meltdowns in the week since the tsunami. While the reactor cores where energy is generated are a concern, water in the pools used to store used nuclear fuel are also major worries. Water in at least one fuel pool - in the complex's Unit 3 - is believed to be dangerously low, exposing the stored fuel rods. Without enough water, the rods may heat further and spew out radiation.
"Dealing with Unit 3 is our utmost priority," Chief Cabinet Secretary Yukio Edano told reporters.
Frantic efforts were made Thursday to douse a number of units with water, and authorities were preparing to repeat many of those efforts Friday. However, they said they would not continue helicopter drops of water. Televised footage of the air drops Thursday appeared to show much of that water blowing away.
Friday's smoke came from the complex's Unit 2, and its cause was not known, the nuclear safety agency said. An explosion had hit the building on Tuesday, possibly damaging a crucial cooling chamber that sits below the reactor core.
In the week since the massive earthquake and tsunami that set off the nuclear crisis by knocking out power to cooling systems for the reactors, Japan's government and the utility that runs Fukushima have struggled to contain the plant's cascading troubles.
"We see it as an extremely serious accident," Yukiya Amano, the head of the U.N.'s International Atomic Energy Agency, told reporters Friday just after arriving in Tokyo. "The international community is extremely concerned."
"This is not something that just Japan should deal with, and people of the entire world should cooperate with Japan and the people in the disaster areas," he said.
If there is good news, it's that the bad situation has not grown significantly more troubled in recent days.
A senior official with the U.N. nuclear agency said Thursday there had been "no significant worsening" at the Fukushima Dai-ichi nuclear plant but that the situation remained "very serious." Graham Andrew told reporters in Vienna that nuclear fuel rods in two reactors were only about half covered with water, and they were also not completely submerged in a third.
Edano said Friday that Tokyo is asking the U.S. government for help and the two are discussing the specifics.
"We are coordinating with the U.S. government as to what the U.S. can provide and what people really need," Edano said. At times, the two close allies have offered starkly differing assessments over the dangers at Fukushima.
U.S. Nuclear Regulatory Commission Chairman Gregory Jazcko said Thursday that it could take days and "possibly weeks" to get the complex under control. He defended the U.S. decision to recommend a 50-mile (80-kilometer) evacuation zone for its citizens, wider than the 30-mile (50-kilometer) band Japan has ordered.
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011 81 90 7170 4769
011 81 90 3080 6711