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NY Times March 13, 2011
Japanese Scramble to Avert Meltdowns as Nuclear Crisis Deepens After Quake
By HIROKO TABUCHI and MATTHEW L. WALD
TOKYO — Japanese officials struggled on Sunday to contain a widening
nuclear crisis in the aftermath of a devastating earthquake and tsunami,
saying they presumed that partial meltdowns had occurred at two crippled
reactors and that they were bracing for a second explosion, even as they
faced serious cooling problems at four more reactors.
The emergency appeared to be the worst involving a nuclear plant since
the Chernobyl disaster 25 years ago. The developments at two separate
nuclear plants prompted the evacuation of more than 200,000 people.
Japanese officials said they had also ordered up the largest
mobilization of their Self-Defense Forces since World War II to assist
in the relief effort.
On Saturday, Japanese officials took the extraordinary step of flooding
the crippled No. 1 reactor at Fukushima Daiichi Nuclear Power Station,
170 miles north of Tokyo, with seawater in a last-ditch effort to avoid
a nuclear meltdown. That came after an explosion caused by hydrogen that
tore the outer wall and roof off the building housing the reactor,
although the steel containment of the reactor remained in place.
Then on Sunday, cooling failed at a second reactor — No. 3 — and core
melting was presumed at both, said the top government spokesman, Chief
Cabinet Secretary Yukio Edano. An explosion could also rock the No. 3
reactor, Mr. Edano warned, because of a buildup of hydrogen within the
reactor.
“The possibility that hydrogen is building up in the upper parts of the
reactor building cannot be denied. There is a possibility of a hydrogen
explosion,” Mr. Edano said. He stressed that as in the No. 1 unit, the
reactor’s steel containment would withstand the explosion.
“It is designed to withstand shocks,” he said.
Officials also said they would release steam and inject water into a
third reactor at the Fukushima Daiichi plant after temperatures rose and
water levels fell around the fuel rods.
Cooling had failed at three reactors at a nuclear complex nearby,
Fukushima Daini, although he said conditions there were considered less
dire for now.
With high pressure inside the reactors at Daiichi hampering efforts to
pump in cooling water, plant operators had to release radioactive vapor
into the atmosphere. Radiation levels outside the plant, which had
retreated overnight, shot up to 1,204 microsieverts per hour, or over
twice Japan’s legal limit, Mr. Edano said.
NHK, Japan’s public broadcaster, flashed instructions to evacuees: close
doors and windows; place a wet towel over the nose and mouth; cover up
as much as possible. At a news conference, Mr. Edano called for calm.
“If measures can be taken, we will be able to ensure the safety of the
reactor,” he said.
Even before Mr. Edano’s statement on Sunday, it was clear from the
radioactive materials turning up in trace amounts outside the reactors
that fuel damage had occurred. The existence or extent of melting might
not be clear until workers can open the reactors and examine the fuel,
which could be months from now.
The Japanese Nuclear and Industrial Safety Agency said that as many as
160 people may have been exposed to radiation around the plant, and
Japanese news media said that three workers at the facility were
suffering from full-on radiation sickness.
Even before the explosion on Saturday, officials said they had detected
radioactive cesium, which is created when uranium fuel is split, an
indication that some of the nuclear fuel in the reactor was already damaged.
How much damage the fuel suffered remained uncertain, though safety
officials insisted repeatedly through the day that radiation leaks
outside the plant remained small and did not pose a major health risk.
However, they also told the International Atomic Energy Agency that they
were making preparations to distribute iodine, which helps protect the
thyroid gland from radiation exposure, to people living near Daiichi and
Daini.
Worries about the safety of the two plants worsened on Saturday because
executives of the company that runs them, Tokyo Electric Power, and
government officials gave confusing accounts of the location and causes
of the dramatic midday explosion and the damage it caused.
Late Saturday night, officials said that the explosion at Daiichi
occurred in a structure housing turbines near its No. 1 reactor at the
plant, rather than inside the reactor itself. But photographs of the
damage did not make clear that this was the case.
They said that the blast, which may have been caused by a sharp buildup
of hydrogen when the reactor’s cooling system failed, destroyed the
concrete structure surrounding the reactor but did not collapse the
critical steel container inside. This pattern of damage cast doubt on
the idea that the explosion was in the turbine building.
“We’ve confirmed that the reactor container was not damaged,” Mr. Edano
said in a news conference on Saturday night. “The explosion didn’t occur
inside the reactor container. As such there was no large amount of
radiation leakage outside. At this point, there has been no major change
to the level of radiation leakage outside, so we’d like everyone to
respond calmly.”
On Sunday morning, an official with Tokyo Electric Power said that the
emergency cooling system at the No. 3 reactor at Daiichi had stopped
working. The official, Atsushi Sugiyama, said that urgent efforts were
being made to cool the reactor with water, and that, as with the first
reactor, there would be a release of vapor containing trace amounts of
radiation to relieve a buildup of pressure.
Japanese nuclear safety officials and international experts said that
because of crucial design differences, the release of radiation at
Daiichi would most likely be much smaller than at Chernobyl even if the
plant had a complete core meltdown, which they said it had not.
After a full day of worries about the radiation leaking at Daiichi,
Tokyo Electric Power said an explosion occurred “near” the No. 1 reactor
at Daiichi around 3:40 p.m. Japan time on Saturday. It said four of its
workers were injured in the blast.
The decision to flood the reactor core with corrosive seawater, experts
said, was an indication that Tokyo Electric Power and Japanese
authorities had probably decided to scrap the plant. “This plant is
almost 40 years old, and now it’s over for that place,” said Olli
Heinonen, the former chief inspector for the I.A.E.A., and now a
visiting scholar at Harvard.
Mr. Heinonen lived in Japan in the 1980s, monitoring its nuclear
industry, and visited the stricken plant many times. Based on the
reports he was seeing, he said he believed that the explosion was caused
by a hydrogen formation, which could have begun inside the reactor core.
“Now, every hour they gain in keeping the reactor cooling down is
crucial,” he said.
But he was also concerned about the presence of spent nuclear fuel in a
pool inside the same reactor building. The pool, too, needs to remain
full of water to suppress gamma radiation and prevent the old fuel from
melting. If the spent fuel is also exposed — and so far there are only
sketchy reports about the condition of that building — it could also
pose a significant risk to the workers trying to prevent a meltdown.
Both Daiichi and Daini were shut down by Friday’s earthquake, but the
loss of power in the area and damage to the plants’ generators from the
ensuing tsunami crippled the cooling systems. Those are crucial after a
shutdown to cool down the nuclear fuel rods.
The malfunctions allowed pressure to build up beyond the design capacity
of the reactors. Early Saturday, officials had said that small amounts
of radioactive vapor were expected to be released into the atmosphere to
prevent damage to the containment systems and that they were evacuating
people in the area as a precaution.
Those releases apparently did not prevent the buildup of hydrogen inside
the plant, which ignited and exploded Saturday afternoon, government
officials said. They said the explosion itself did not increase the
amount of radioactive material being released into the atmosphere.
However, safety officials urged people who were not evacuating but still
lived relatively nearby to cover their mouths and stay indoors.
David Lochbaum, who worked at three reactors in the United States with
designs similar to Daiichi, and who was later hired by the Nuclear
Regulatory Commission to teach its personnel about that technology, said
that judging by photographs of the stricken plant, the explosion
appeared to have occurred in the turbine hall, not the reactor vessel or
the containment that surrounds the vessel.
The Daiichi reactor is a boiling-water reactor. Inside the containment,
the reactor sends its steam out to a turbine. The turbine converts the
steam’s energy into rotary motion, which turns a generator and makes
electricity.
But as the water goes through the reactor, some water molecules break up
into hydrogen and oxygen. A system in the turbine hall usually scrubs
out those gases. Hydrogen is also used in the turbine hall to cool the
electric generator. Hydrogen from both sources has sometimes escaped and
exploded, Mr. Lochbaum said, but in this case, there is an additional
source of hydrogen: interaction of steam with the metal of the fuel
rods. Operators may have vented that hydrogen into the turbine hall.
Earlier Saturday, before the explosion, a Japanese nuclear safety panel
said the radiation levels were 1,000 times above normal in a reactor
control room at Daiichi. Some radioactive material had also seeped
outside, with radiation levels near the main gate measured at eight
times normal levels, NHK quoted nuclear safety officials as saying.
The emergency at Daiichi began shortly after the earthquake struck
Friday afternoon. Emergency diesel generators, which kicked in to run
the cooling system after the electrical power grid failed, shut down
about an hour after the earthquake. There was speculation that the
tsunami had flooded the generators, knocking them out of service.
For some time, the plant was able to operate in a battery-controlled
cooling mode. Tokyo Electric Power said that by Saturday morning it had
also installed a mobile generator to ensure that the cooling system
would continue operating even after reserve battery power was depleted.
Even so, the company said it needed to conduct “controlled containment
venting” in order to avoid an “uncontrolled rupture and damage” to the
containment unit.
Why the controlled release of pressure did not succeed in addressing the
problem was not immediately explained. Tokyo Electric Power and
government nuclear safety officials also did not explain the precise
sequence of failures at the plant.
Daiichi and other nuclear facilities are designed with extensive backup
systems that are supposed to function in emergencies to ensure the
plants can be shut down safely.
Hiroko Tabuchi reported from Tokyo, and Matthew L. Wald from Washington.
Martin Fackler contributed reporting from Nakaminato, Japan, David E.
Sanger from Washington, and Michael Wines from Tokyo.
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