w*p
发帖数: 16484 | 1 In Japan plant, frantic efforts to avoid meltdown
Police officers wearing gas masks patrol in the area of the Fukushima power
plant's Unit 1 in Okumamachi, Fukushima Prefecture (state), northern Japan
AP – Police officers wearing gas masks patrol in the area of the Fukushima
power plant's Unit 1 in Okumamachi, …
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CBC.ca
By MARI YAMAGUCHI and JEFF DONN, Associated Press Mari Yamaguchi And Jeff
Donn, Associated Press – 42 mins ago
TOKYO – Inside the troubled nuclear power plant, officials knew the risks
were high when they decided to vent radioactive steam from a severely
overheated reactor vessel. They knew a hydrogen explosion could occur, and
it did. The decision still trumped the worst-case alternative — total
nuclear meltdown.
At least for the time being.
The chain of events started Friday when a magnitude-8.9 earthquake and
tsunami severed electricity to the Fukushima Dai-ichi nuclear complex 170
miles (270 kilometers) northeast of Tokyo, crippling its cooling system.
Then, backup power did not kick in properly at one of its units.
From there, conditions steadily worsened, although government and nuclear
officials initially said things were improving. Hours after the explosion,
they contended that radiation leaks were reduced and that circumstances had
gotten better at the 460-megawatt Unit 1. But crisis after crisis continued
to develop or be revealed.
Without power, and without plant pipes and pumps that were destroyed in the
explosion of the most-troubled reactor's containment building, authorities
resorted to drawing seawater in an attempt to cool off the overheated
uranium fuel rods.
Robert Alvarez, senior scholar at the Institute for Policy Studies and
former senior policy adviser to the U.S. secretary of energy, said in a
briefing for reporters that the seawater was a desperate measure.
"It's a Hail Mary pass," he said.
He said that the success of using seawater and boron to cool the reactor
will depend on the volume and rate of their distribution. He said the
dousing would need to continue nonstop for days.
Another key, he said, was the restoration of electrical power, so that
normal cooling systems can be restored.
Officials placed Dai-ichi Unit 1, and four other reactors, under states of
emergency Friday because operators had lost the ability to cool the reactors
using usual procedures.
An additional reactor was added to the list early Sunday, for a total of six
— three at the Dai-ichi complex and three at another nearby complex. Local
evacuations have been ordered at each location. Japan has a total of 55
reactors spread across 17 complexes nationwide.
Officials began venting radioactive steam at Fukushima Dai-ichi's Unit 1 to
relieve pressure inside the reactor vessel, which houses the overheated
uranium fuel.
Concerns escalated dramatically Saturday when that unit's containment
building exploded.
It turned out that officials were aware that the steam contained hydrogen,
acknowledged Shinji Kinjo, spokesman for the government Nuclear and
Industrial Safety Agency. More importantly, they also were aware they were
risking an explosion by deciding to vent the steam.
The significance of the hydrogen began to come clear late Saturday:
_Officials decided to reduce rising pressure inside the reactor vessel, so
they vented some of the steam buildup. They needed to do that to prevent the
entire structure from exploding, and thus starting down the road to a
meltdown.
_At the same time, in order to keep the reactor fuel cool, and also prevent
a meltdown, operators needed to keep circulating more and more cool water on
the fuel rods.
_Temperature in the reactor vessel apparently kept rising, heating the
zirconium cladding that makes up the fuel rod casings. Once the zirconium
reached 2,200 degrees Fahrenheit (1,200 Celsius), it reacted with the water,
becoming zirconium oxide and hydrogen.
_When the hydrogen-filled steam was vented from the reactor vessel, the
hydrogen reacted with oxygen, either in the air or water outside the vessel,
and exploded.
A similar "hydrogen bubble" had concerned officials at the 1979 Three Mile
Island nuclear disaster in Pennsylvania until it dissipated.
If the temperature inside the Fukushima reactor vessel continued to rise
even more — to roughly 4,000 degrees Fahrenheit (2,200 Celsius) — then the
uranium fuel pellets would start to melt.
According to experts interviewed by The Associated Press, any melted fuel
would eat through the bottom of the reactor vessel. Next, it would eat
through the floor of the already-damaged containment building. At that point
, the uranium and dangerous byproducts would start escaping into the
environment.
At some point in the process, the walls of the reactor vessel — 6 inches (
15 centimeters) of stainless steel — would melt into a lava-like pile,
slump into any remaining water on the floor, and potentially cause an
explosion much bigger than the one caused by the hydrogen. Such an explosion
would enhance the spread of radioactive contaminants.
If the reactor core became exposed to the external environment, officials
would likely began pouring cement and sand over the entire facility, as was
done at the 1986 Chernobyl nuclear accident in the Ukraine, Peter Bradford,
a former commissioner of the U.S. Nuclear Regulatory Commission, said in a
briefing for reporters.
Another expert on the call, Ken Bergeron, a physicist and former Sandia
scientist, added that as a result of such a meltdown the surrounding land
would be off-limits for a considerable period of time, and "a lot of first
responders would die."
___
AP National Writer Jeff Donn reported from Boston. | w*p
发帖数: 16484 | | A*******e
发帖数: 12486 | 3 操，这么严重，哪像yoh等人说得那么乐观
power
Fukushima
had
continued
the
reactors
six
Local
to
the
prevent
on
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,
【在 w*p 的大作中提到】
: In Japan plant, frantic efforts to avoid meltdown
: Police officers wearing gas masks patrol in the area of the Fukushima power
: plant's Unit 1 in Okumamachi, Fukushima Prefecture (state), northern Japan
: AP – Police officers wearing gas masks patrol in the area of the Fukushima
: power plant's Unit 1 in Okumamachi, …
: * Ring of Fire Play Video Earthquakes Video:Ring of Fire ABC News
: * Greg Palkot Live In Japan Play Video Earthquakes Video:Greg Palkot
: Live In Japan FOX News
: * Withstanding quakes Play Video Earthquakes Video:Withstanding quakes
: CBC.ca
| y**u
发帖数: 7459 | 4 他讲的一听就不靠谱。有些话不错，但是他全往最好的方向靠。
【在 A*******e 的大作中提到】
: 操，这么严重，哪像yoh等人说得那么乐观
:
: power
: Fukushima
: had
: continued
: the
: reactors
: six
: Local
| T*********r
发帖数: 11175 | 5 下午一点已经开始往三号堆注海水了
这事基本就算过去了应该
【在 y**u 的大作中提到】
: 他讲的一听就不靠谱。有些话不错，但是他全往最好的方向靠。
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