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Military版 - Ocean Spill Feared as Toxic Water Rises; Plutonium Found in Soil
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话题: water话题: reactor话题: monday话题: tepco话题: said
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http://online.wsj.com/article/SB1000142405274870447190457622801
* MARCH 28, 2011, 4:56 P.M. ET
By MITSURU OBE
TOKYO—Workers at Japan's damaged Fukushima Daiichi nuclear plant faced a
new threat Monday as they battled to keep toxic water from spilling into the
ocean, as the water's radiation levels offered the strongest sign yet that
the core of one reactor may have partially melted.
Also late Monday, plant operator Tokyo Electric Power Co. said that small
quantities of plutonium were detected in samples of soil taken from the
nuclear plant's compounds. They pose no risk to human health, the company
said, and are unlikely to affect the repair work. But the discovery of
highly toxic plutonium is expected to add to the urgency of the task to
bring the reactors under control.
View Full Image
0328jnuke2
European Pressphoto Agency
Nuclear and Industrial Safety Agency (NISA) deputy director general Hidehiko
Nishiyama gives a daily report in Tokyo, Monday.
0328jnuke2
0328jnuke2
Monday's events added a new layer of urgency to the battle to stem disaster
at the hobbled nuclear complex. Since Japan's March 11 earthquake and
tsunami knocked out cooling systems at the plant, the prime battle has been
to bring overheating reactors under control. Temperatures stopped rising
last week after crews doused reactors with salt- and fresh water. But plant
officials are now coming to grips with standing water at four of the
reactors—at least one of the pools containing highly radioactive water—
that pose dangers to personnel on the site and could challenge further
efforts.
The plutonium that Tepco reported Monday was found after workers tested five
sites around the plant on March 21 and 22. The highest readings by far were
from an athletic field for employees, not next to any reactor. Some spots
showed no results, making pinpointing a source difficult. Neither the
company nor government officials released further information late Monday.
View Slideshow
[SB10001424052748704471904576228142696830816]
Kazuhiro Nogi/Agence France-Presse/Getty Images
Tsuyako Ito, at a shelter in Kamaishi, Iwate prefecture, on March 25, is the
'last geisha' of this once-bustling steel city.
The amounts found at the field—0.54 becquerel per kilogram for plutonium
238 and 0.27 per kilogram each for plutonium 239 and plutonium 240—are
considered small and unlikely to hinder work at the plant. But they could
pose a major obstacle if levels rise because plutonium is highly radioactive.
At the troubled reactor No. 2, standing water has reached a depth of one
meter, according to Tepco.
Water in an underground trench that houses pipes in the No. 2 reactor had a
radioactivity level of 1,000 millisieverts per hour, officials said. That is
four times as great as the cumulative annual limit emergency workers at the
facility are allowed to receive.
Radiation Levels in Japan
View Interactive
The Japanese government monitors radiation levels around the country. Track
these measurements over time.
Reactor Monitor
View Interactive
Japan's nuclear regulator said the water would begin to leak into the ocean
through a shaft if it rose another meter. Officials at Tepco said they were
exploring ways to put pumps at the site despite the water's radioactivity.
Also Monday, government officials said the radiation level in the water at
No. 2 offered the strongest indication yet that the fuel there may have
partially melted after the March 11 earthquake and tsunami struck the plant.
Previously, officials had theorized that exposed fuel rods may have
partially melted in the days following the quake.
A partial melting can release large amounts of radioactivity and threaten
the environment if the reactor vessels designed to prevent the release of
that radioactivity fail. It can also make the reactor harder to control if
it begins to heat again significantly, though workers have kept its
temperature steady for about a week.
Radioactivity soars inside Japanese reactors as hundreds of antinuclear
demonstrators take to the streets in Tokyo. Video courtesy of Reuters.
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A partial melting falls short of a nuclear meltdown—an imprecise term that
often refers to fuel that melts, flows to the bottom of the reactor vessel
that houses the fuel and then melts through it.
The findings also renewed speculation among observers about the integrity of
the pressure vessel of reactor No. 2, which houses the fuel rods behind a
thick curtain of steel—though government officials said there was no
evidence of such a breach. They also make the No. 2 reactor the main focus
of government and company officials battling to set up crucial cooling
systems at the plant.
"We have received the analysis estimating that the water that came in
contact with the melted fuel in the containment building has somehow leaked
out," chief government spokesman Yukio Edano said in a press conference on
Monday. The containment building houses the reactor.
Radiation levels in the water around Japan's Fukushima nuclear plant spiked
over the weekend, setting back plans to get the plant under control. WSJ's
Mariko Sanchanta and Yumiko Ono discuss.
Monday's developments don't indicate a resumption of the dangerous heating
that followed the quake and turned the situation into a major nuclear crisis
. But the potential to spill water into the sea or elsewhere raise fears of
increased discharges of radiation that have already led to positive, if
relatively low, findings in some food and water in the surrounding area. It
also complicates efforts to keep the reactor cool because they depend on
using large amounts of water.
Officials at Japan's Nuclear and Industrial Safety Agency reiterated Monday
that they believe reports of radiation in the ocean near the plant likely
stem from airborne radioactive particles that subsequently fell into the
ocean water, not direct leaks from the plant into the ocean.
However, Hidehiko Nishiyama, a senior regulator at the agency, said a runoff
of toxic water from the surface of the facility may have reached the ocean.
View Full Image
0328jnuke
Reuters
Yumi Saitou, who lives in Fukushima, is silhouetted as she is tested for
possible nuclear radiation at an evacuation centre in Fukushima, northern
Japan, on Monday.
0328jnuke
0328jnuke
Meanwhile, levels of radioactive iodine-131 in the ocean appeared to level
off, falling to 250 times the allowable limit at a location tested Sunday
south of a discharge outlet for reactor Nos. 1-4. The level had stood at 1,
850.5 times the legal limit on Saturday.
In addition to the meter-deep standing water at reactor No. 3, Tepco
reported a half-meter or less at units 1 and 3. The water found in the
trench at the No. 1 unit was determined to have a radioactivity level of 0.4
millisievert per hour, a small fraction of that at No. 2. The reading for
the No. 3 reactor couldn't be confirmed, but authorities believe its
radiation level is similar to the water from the No. 1 unit.
Tepco didn't say if water at No. 4, which also stood nearly a meter deep
showed elevated radioactivity.
Separately on Monday, Tepco said President Masataka Shimizu fell ill earlier
this month and spent several days—it wasn't immediately clear how many—
away from crisis headquarters starting March 16. The company said that
during his time away, Mr. Shimizu, who hasn't been seen in public since
March 13, continued to monitor the situation from another part of Tepco's
home office.
Mr. Nishiyama, the senior government regulator, said the executive is back
at work. He said Mr. Shimizu's absence didn't affect cooperation between the
company and the government, and said the utility executive was currently
engaged in addressing the crisis.
Also on Monday, speculation grew in Japan that Tepco could be subject to
government takeover amid fears over how it would handle its liabilities, and
Tepco shares hit a 34-year low. A spokesman for Prime Minister Naoto Kan
said nationalization isn't on the agenda.
Tepco said Monday it had reached out to companies in the U.S., South Korea
and France to provide an array of equipment including masks, filters, clean
gloves, protective suits.
It is unclear where the water flooding the buildings is coming from, but
levels have risen dramatically since Thursday, when three workers stepped in
roughly 15 centimeters of contaminated water and later needed to be
hospitalized.
Members of the Japanese military and firefighters from around the country
have doused the damaged units with both seawater and freshwater. That water
has splashed over spent-fuel-rod pools, which are housed above each reactor,
as well as over the reactors themselves. The have also injected water
directly into the cooling systems of the facility's units.
Some experts are focusing on the possibility that one of the scores of
valves and pipes that run in and out of the containment vessel may have
snapped. Agency officials say the cannot rule out the possibility that the
radioactive water indicates that the pressure vessel of reactor No. 2 —
which contains the core—has been damaged. But they also say they have no
evidence it has been.
If the reactor pressure vessel is damaged, melted fuel could escape into the
containment vessel, which serves as the final barrier.
Hiroaki Koide, an assistant professor of Kyoto University's Research Reactor
Institute, said the containment vessel's main valve may be broken, allowing
radioactive steam to escape.
"All the seawater that has been poured in to cool the reactor immediately
evaporated into steam and escaped from the broken valve," Mr. Koide said. "
As it contacted the outside air, it condensed into water and soaked the
building."
The pooling radioactive water also raise new questions for the government
and Tepco. Among the most pressing: What to do with it?
Draining the water into the nearby Pacific Ocean, where spots close to
Fukushima Daiichi have already shown elevated radiation readings, is out of
the question because its high radioactivity would likely damage the
environment. An early plan to store it in the condensers, which are normally
used to convert the steam that powers the plant's turbines into water, has
been delayed because that machinery is already full.
Officials have said they would consider bringing in an outside container to
store the water if a suitable receptacle can be found. It could also be used
as coolant and run back into the reactor.
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相关话题的讨论汇总
话题: water话题: reactor话题: monday话题: tepco话题: said