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Fukushima Meltdown Mitigation Aims to Prevent Radioactive
Flood
http://www.emfnews.org
Three months after its meltdown, the
stricken nuclear power plant continues to struggle to cool
its nuclear fuel--and cope with growing amounts of
radioactive cooling water
By David Biello |
June 24, 2011
More than three months after a powerful
earthquake and 14-meter-high tsunami struck Japan, the
Fukushima Daiichi nuclear power plant remains flooded with a
salty mix of ocean and fresh water that is contaminated with
the radioactive residue of three reactors and four spent
fuel pools' worth of nuclear fuel. Every day an additional
500 metric tons of seawater is poured onto the still hot
nuclear fuel in the stricken reactors and fuel pools. More
than 100,000 metric tons of such water now sits in the
basement and trenches of the reactors—or evaporates inside
the hot reactor buildings, making for a radioactive
onsen (hot bath).
Thus far, neither the nation's 75 aftershocks of magnitude
6.0 or greater—the latest of which struck on June 23—nor
inclement weather has halted ongoing efforts to cool the
stricken nuclear power plant. With the start of any
decommissioning process still at least year away, cooling
the fuel with water remains the focus—as well as a potential
source of additional problems as contaminated water
threatens to overwhelm the plant and its environs.
In early June Tokyo Electric Power Co. (TEPCO) installed a
series of devices—from nuclear equipment manufacturers
Kurion and Areva Group—meant to filter radioactive material
from the contaminated cooling water and enable it to be
reused on the hot nuclear fuel rods. Without such
filtration, radiation levels in the reactor buildings can
climb too high to permit workers to advance their efforts to
control and clean up the damaged power plant. But a trial
run of the new filtration system was halted on June 18 in
less than five hours when it captured as much radioactive
cesium 137 in that span as was expected to be filtered in a
month.
Massive tanks have been delivered to store some of the
excess radioactive water, given that spraying must continue
due to leaks in the reactors themselves that prevent
restoration of the normal cooling system. "The most
important thing is to keep the reactor fuel cool. If the
only alternative is to use saltwater then that's the best
thing to do," said Bill Borchardt, executive director for
operations at the U.S. Nuclear Regulatory Commission (NRC)
at a talk in May. "Given the situation that existed and that
there were very few options available, I think injection of
saltwater was clearly the appropriate thing to do," although
TEPCO has switched to using fresh water more recently.
With just centimeters remaining before the radioactive water
overtops its storage, however, another release of
contaminated water into the ocean looks ever more likely.
Already, pools of this water burned at least two workers at
the plant when they stepped in the puddles, and TEPCO was
forced to dump more than 11,000 metric tons of such
contaminated water in early April.
"The reactors weren't designed to have water poured in the
top, pour out the bottom and pool in the basement," says
nuclear energy advisor Arnie Gundersen of Fairewinds
Associates consultants. "What TEPCO should be doing is
building a trench around the reactors down to bedrock, 20
meters deep and 1.5 meters wide, and fill that trench with
zeolite." Zeolite minerals capture radioactive particles,
and are used in the reprocessing of spent nuclear fuel.
The normal equipment for such cooling is inoperable thanks
to the complete meltdown and corrosion from seawater, so
spraying new water on the hot nuclear fuel remains the only
option. Debris and detritus—radioactive and inert,
alike—continue to impair human and robot workers' attempts
to achieve so-called "cold shutdown," which would allow the
real work of tearing down and cleaning up the contaminated
site to begin.
"It's going to be very complicated to decommission this
thing," physicist Arjun Makhijani, president of the
Institute for Energy and Environmental Research notes. "The
handling equipment has been destroyed, it was a complete
meltdown, it's a highly radioactive environment and there's
radioactive water."
The rising level of used cooling water is just one of the
challenges at the plant, more than three months after the
crisis started. Radiation levels continue to spike at times
as high as 4,000 millisieverts an hour, impairing repair
efforts, even with robots. (A sievert is a unit of ionizing
radiation equal to 100 rems; a rem is a dosage unit of x-ray
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}div.Section1 { page: Section1; } Despite the restoration of
electric power in April, cooling systems remain inoperable.
And radioactive material—cesium 134, cesium 137 and some 50
other longer-lived radioactive isotopes—continue to be found
farther and farther afield from the site itself,
concentrating in hot spots as far as 225 kilometers from the
stricken complex. For its part, Japan's Nuclear and
Industrial Safety Agency now estimates Fukushima has
released some 770,000 terabecquerels worth of radiation—or
roughly 15 percent of the amount released by the
catastrophic 1986 fire at Chernobyl in Ukraine. (One
becquerel represents the rate of radioactive decay—or
radiation emitted by a substance—as one disintegration, or
count, per second.)
"When you have an accident for months and certain patterns
of rainfall, you get hot spots," Makhijani says. As a
result, entire towns, such as Date, Iitate and Iwaki City,
may have to be permanently abandoned and roughly 80,000
people have lost their homes to radioactive contamination.
In addition to the failed water filtration system, TEPCO has
proposed enshrouding in plastic the reactor buildings torn
apart by hydrogen explosions to prevent further releases
from that source of radioactive material. The good news is
that the heat from the melted down nuclear fuel and still
intact fresh fuel rods continues to decline. "As time goes
on, the decay heat gets less and less," the NRC's Borchardt
noted. "Around 90 to 100 days the problem becomes much less
severe"—a time period Fukushima Daiichi has now entered.
More than 3,700 workers continue to attempt to control and
contain the crisis. Nine of those workers have already
reached the legal "emergency limit" of 250 millisieverts of
cumulative radiation exposure, and 124 have received more
than 100 millisieverts, the prior limit. In the U.S. annual
exposure for nuclear power plant workers is limited to 50
millisieverts per year, and it is estimated by some that
their risk of cancer increases by 4 percent per sievert.
(This risk figure remains controversial as either too high
or too low, by scientists who study the impact of radiation
on health, primarily based on data collected after the 1945
detonation of the atomic bombs over Hiroshima and Nagasaki
during World War II.)
In the end TEPCO plans call for a cold shutdown of the
stricken reactors by April 2012—more than a year after the
crisis began—and that means some kind of treatment plan for
hundreds of thousands of metric tons of radioactive cooling
water will be needed as soon as possible. Beyond that lies
the challenge of hundreds of thousands of metric tons of
soil contaminated with radioactive isotopes across at least
600 square kilometers of northeastern Japan.
The challenge is not insurmountable, just costly. "You can
clean up almost anything if you're prepared to spend enough
money on it," adds Peter Bradford, a former member of the
NRC.
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