h****r
发帖数: 2056 | 1 Eastern-Pacific Jet Stream的主力（超过2/3的覆盖面积）直扑北加州而来。
夏威夷，南加不再风道上。 | h****r
发帖数: 2056 | 2 Japan nuclear alert at Fukushima - Q&A
15 March 11 12:19 GMT
There have been two explosions at the Fukushima Daiichi nuclear power plant
in Japan, following Friday's earthquake and tsunami, and a third reactor is
reportedly at risk of fuel-rod meltdown.
How great a danger do these problems pose for people in Japan and further
afield?
Has there been a leakage of radioactive material?
Yes. Local government officials in Fukushima say 190 people have been
exposed to some radiation. An American warship, the USS Ronald Reagan, has
detected low levels of radiation at a distance of 100 miles (161km) from the
Fukushima plant.
How much radioactive material has escaped?
The Japanese authorities say only low levels of radiation have been detected
outside the plant. The International Atomic Energy Agency has described it
as a level four event on the International Nuclear and Radiological Event
Scale (INES), which is used for an accident "with local consequences". No
abnormal levels of radiation have been detected in Russia.
What type of radioactive material has escaped?
There are reports of radioactive isotopes of caesium and iodine in the
vicinity of the plant. Experts say it would be natural for radioactive
isotopes of nitrogen and argon to have escaped as well. There is no evidence
that any uranium or plutonium has escaped.
What harm do these radioactive materials cause?
Radioactive iodine could be harmful to young people living near the plant.
After the 1986 Chernobyl nuclear disaster there were some cases of thyroid
cancer as a result. However, people who were promptly issued with iodine
tablets ought to be safe. Radioactive caesium accumulates in soft tissue,
while plutonium accumulates in the bone and liver. Radioactive nitrogen
decays within seconds of its release, and argon poses no threat to health.
How did the radioactive materials escape?
There have been problems with cooling systems, causing the reactors to
overheat. Production of steam has caused pressure to build up inside the
reactor, so small amounts of steam have been deliberately released. On
Tuesday another reactor exploded, possibly causing a crack in its
suppression chamber. This would allow steam to escape continuously, but the
situation is unclear. Experts say that the presence in the steam of caesium
and iodine - which are among the by-products of nuclear fission - suggests
that the metal casing of some of the fuel rods has melted or broken. But the
uranium fuel itself has a very high melting point so it is less likely to
have melted, let alone vapourised.
Could radioactive materials have escaped by any other means?
The authorities have pumped sea water into three reactors. This water will
be contaminated by its passage through the reactor, but it is currently
unclear whether any of it has been released into the environment.
How long will any contamination last?
Radioactive iodine decays quite quickly. Most will have disappeared within a
month. Radioactive caesium does not last long in the body - most has gone
within a year. However, it lingers in the environment and can continue to
present a problem for many years.
Has there been a meltdown?
The term "meltdown" is used in a variety of ways. As noted above, the
reported detection of radioactive caesium and iodine may indicate that some
of the metal casing enclosing the reactors' uranium fuel has melted (a "fuel
-rod meltdown"). However, there is as yet no indication that the uranium
fuel itself has melted. Still less is there any indication of a "China
Syndrome" where the fuel melts, gathers below the reactor and resumes a
chain reaction, that enables it to melt everything in its way, and bore a
path deep into the earth. If there were to be a serious meltdown, the
Japanese reactor is supposed to be able to handle it, preventing the China
Syndrome from taking place. Reports suggest that underneath the reactor,
within the outer containment vessel, there is a concrete basin designed to
capture and disperse any molten fuel.
Could there be a Chernobyl-like disaster?
Experts say this is highly unlikely. The chain reaction at all Fukushima
reactors has ceased. The explosions that have occurred have taken place
outside the steel and concrete containment vessels enclosing the reactors.
At Chernobyl an explosion exposed the core of the reactor to the air, and a
fire raged for days sending its contents in a plume up into the atmosphere.
At Fukushima the explosions - caused by hydrogen and oxygen vented from the
reactor - have damaged only the roof and walls erected around the
containment vessels.
Could there be a nuclear explosion?
No. A nuclear bomb and a nuclear reactor are different things.
What caused the hydrogen release from the reactor?
At high temperatures, steam can separate into hydrogen and oxygen in the
presence of zirconium, the metal used for encasing the reactor fuel. This
mixture is highly explosive.
How do iodine tablets work?
If the body has all the iodine it needs, it will not absorb further iodine
from the atmosphere. The tablets fill the body up with non-radioactive
iodine, which prevent it absorbing the radioactive iodine.
What kind of radiation levels have been recorded at Fukushima?
The Kyodo news agency reports that a radiation level of 1,557 microsieverts
per hour was registered on Sunday. At this level, one hour's exposure is
roughly equivalent to one chest X-ray. Later measurements included 750
microsieverts per hour at 0200 on Monday, and 20 microsieverts per hour at
1145. On a long-haul flight, passengers are exposed to about five
microsieverts per hour. However, after Tuesday's explosion, readings at the
site rose again beyone safe limits - 400 millisieverts per hour and people
living within 20 miles (32km) of the plant were told to stay indoors. Moving
away from the source of radiation, measurements quickly tail off, and in
Tokyo they were reported to have been higher than normal, but officials said
there were no health dangers.
Is any level of exposure to radiation safe?
In some parts of the world, natural background radiation is significantly
higher than others - for example in Cornwall, in south-west England. And yet
people live in Cornwall, and many others gladly visit the area. Similarly,
every international air flight exposes passengers to higher than normal
levels of radiation - and yet people still fly, and cabin crews spend large
amounts of time exposed to this radiation. Patients in hospitals regularly
undergo X-rays. Scientists dispute whether any level of exposure to
radiation is entirely safe, but exposure to some level of radiation -
whether at normal background levels or higher - is a fact of life.
How do Fukushima's problems affect the rest of the world?
It depends on how much radiation is released. At present, the IAEA says the
effects are of a "local" nature. | J******n
发帖数: 1466 | | h****r
发帖数: 2056 | 4 周六报道说估计第一批辐射云本周二抵达夏威夷。
结果两天后偏了航道北上了，现在的趋势是直奔北美大陆来了。
按图上的速度估计130海里一小时，需要大概1600海里。最坏的结果是今天明天就到。
但是政府啥也没说，估计这第一批来了危害也不大，不值得一提。
【在 J******n 的大作中提到】
: 啥时候登陆了，我好提前休假，
| J******n
发帖数: 1466 | 5 我靠，油看比洗而死里，，，今晚开始打包
【在 h****r 的大作中提到】
: 周六报道说估计第一批辐射云本周二抵达夏威夷。
: 结果两天后偏了航道北上了，现在的趋势是直奔北美大陆来了。
: 按图上的速度估计130海里一小时，需要大概1600海里。最坏的结果是今天明天就到。
: 但是政府啥也没说，估计这第一批来了危害也不大，不值得一提。
| d********1
发帖数: 1269 | 6 事实上政府就是个大骗子
【在 h****r 的大作中提到】
: 周六报道说估计第一批辐射云本周二抵达夏威夷。
: 结果两天后偏了航道北上了，现在的趋势是直奔北美大陆来了。
: 按图上的速度估计130海里一小时，需要大概1600海里。最坏的结果是今天明天就到。
: 但是政府啥也没说，估计这第一批来了危害也不大，不值得一提。
| b*******a
发帖数: 38 | | s*********n
发帖数: 1065 | |
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