Fukushima radioactive fallout nears Chernobyl levels
* 17:14 24 March 2011 by Debora
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Japan's damaged nuclear plant in Fukushima has been emitting
radioactive iodine and caesium at levels approaching those seen in
the aftermath of theChernobyl
nuclear-accident.html> in 1986. Austrian researchers have used a
worldwide network of radiation detectors designed to spot clandestine
nuclear bomb tests to show that iodine-131 is being released at
daily levels 73 per cent of those seen after the 1986 disaster. The
daily amount of caesium-137 released from Fukushima Daiichi is
around 60 per cent of the amount released from Chernobyl.
The difference between this accident and
ont-be-another-chernobyl.html>, they say, is that at Chernobyl a
huge fire released large amounts of many radioactive materials,
including fuel particles, in smoke. At Fukushima Daiichi, only the
volatile elements, such as iodine and caesium, are bubbling off the
damaged fuel. But these substances could nevertheless pose a
significant health risk outside the
The organisation set up to verify the Comprehensive Nuclear-Test-Ban
er-us.html> (CTBT) has a global network of air samplers that monitor
and trace the origin of around a dozen radionuclides, the radioactive
elements released by atomic bomb blasts and nuclear accidents.
These measurements can be combined with wind observations to track
where the radionuclides come from, and how much was released.
The level of radionuclides leaking from Fukushima Daiichi has been
unclear, but the CTBT air samplers can shed some light, says Gerhard
Wotawa<http://homepage.boku.ac.at/wotawa/> of Austria's Central
Institute for Meteorology and
For the first two days after the accident, the wind blew east from
Fukushima towards monitoring stations on the US west coast; on the
third day it blew south-west over the Japanese monitoring station
at Takasaki, then swung east again. Each day, readings for iodine-131
at Sacramento in California, or at Takasaki, both suggested the
same amount of iodine was coming out of Fukushima, says Wotawa: 1.2
to 1.3 W 1017 becquerels per day.
The agreement between the two "makes us confident that this is
accurate", he says. So do similar readings at CTBT stations in
Alaska, Hawaii and Montreal, Canada readings at the latter, at
least, show that the emissions have
In the 10 days it burned, Chernobyl put out 1.76 W 1018 becquerels
of iodine-131, which amounts to only 50 per cent more per day than
has been calculated for Fukushima Daiichi. It is not yet clear how
long emissions from the Japanese plant will continue.
Similarly, says Wotawa, caesium-137 emissions are on the same order
of magnitude as at Chernobyl. The Sacramento readings suggest it
has emitted 5 W 1015 becquerels of caesium-137 per day; Chernobyl
put out 8.5 W 1016 in total around 70 per cent more per day.
"This is not surprising," says Wotawa. "When the fuel is damaged
there is no reason for the volatile elements not to escape," and
the measured caesium and iodine are in the right ratios for the
fuel used by the Fukushima Daiichi reactors. Also, the Fukushima
plant has around1760 tonnes of fresh and used nuclear fuel on
sk-at-fukushima.html?rss=1>, and an unknown amount has been damaged.
The Chernobyl reactor had only 180 tonnes.
The amounts being released, he says, are "entirely consistent" with
the relatively low amounts of caesium and iodine being measured in
soil, plants and water in Japan, because so much has blown out to
sea. The amounts crossing the Pacific to places like Sacramento are
vanishingly small they were detected there because the CTBT network
is designed to sniff out the tiniest traces.
The Chernobyl accident emitted much more radioactivity and a wider
diversity of radioactive elements than Fukushima Daiichi has so
far, but it was iodine and caesium that caused most of the health
risk especially outside the immediate area of the Chernobyl plant,
says Malcolm Crick, secretary of a United Nations body that has
byl_Report.pdf> the health effects of Chernobyl. Unlike other
elements, he says, they were carried far and wide by the wind.
Moreover the human body absorbs iodine and caesium readily.
"Essentially all the iodine or caesium inhaled or swallowed crosses
into the blood," says Keith Baverstock<http://www.kbaverstock.org/>,
former head of radiation protection for the World Health Organization's
European office, who has studied Chernobyl's health effects.
Iodine is rapidly absorbed by the thyroid, and leaves only as it
decays radioactively, with a half-life of eight days. Caesium is
absorbed by muscles, where its half-life of 30 years means that it
remains until it is excreted by the body. It takes between 10 and
100 days to excrete half of what has been consumed.
While in the body the isotopes' radioactive emissions can do
significant damage, mainly to DNA. Children who ingest iodine-131
can develop thyroid cancer 10 or more years later; adults seem
relatively resistant.A study published in the US last
week<http://www.nih.gov/news/health/mar2011/nci-17.htm> found that
iodine-131 from Chernobyl is still causing new cases of thyroid
cancer to appear at an undiminished rate in the most heavily affected
regions of Ukraine, Belarus and Russia.
Caesium-137 lingers in the environment because of its long
ffects-of-nuclear-crisis.html> over how much damage environmental
exposure to low doses has done since Chernobyl. Some researchers
think it could still cause thousands of new cases of cancer across
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