Japanese engineers stuffed
sawdust, three garbage bags of shredded newspaper and superabsorbent polymer (SAP)
into an eight-inch reactor containment crack
in a desperate bid to stop radioactive water from leaking into the Pacific
Ocean.
An earlier effort to fill the hole with concrete failed.
"We will continue to take all measures to ensure the safety
and to continue monitoring the surrounding environment around the Power
Station," the Tokyo Electric Power Co. said in an official statement regarding
conditions at the Fukushima Daiichi Nuclear Power Station, which suffered the
double whammy of an earthquake and a tsunami on March 11.
News reports indicated that the polymer mix was not
initially successful and that workers were stirring the mix in order to
activate the polymers.
Design News could
not ascertain the supplier of the polymer or the specific formulation last
night.
That information is critical because superabsorbent polymers
are highly engineered to perform specific tasks. It seems logical that the
polymers came from a Japanese source, however, since there are major chemical
companies there that manufacture SAPs.
They were first developed in the 1960s by the U.S. Department
of Agriculture. Their basic chemistry is
fascinating.
The USDA was researching materials that could improve water
conservation in soils. USDA scientists designed a resin based on the grafting
of acrylonitrile polymer onto the backbone of starch molecules. The hydrolyzed
product produced water absorption greater than 400 times its weight.
Conventional natural materials such as cotton and sponges can only absorb up to
20 times their weight.
Japanese companies began independent research to develop
their own technology, and focused on use of starch, carboxy methyl cellulose
(CMC), acrylic acid, polyvinyl alcohol (PVA) and isobutylene maleic anhydride
(IMA).
Early Japanese researchers worked at Sanyo Chemical,
Sumitomo Chemical, Kao, Nihon Starch and Japan Exlan. Other global players included
Dow Chemical, Hercules, General Mills Chemical, DuPont, National Starch &
Chemical and Enka (Akzo), according to a history by M2 Polymer
Technologies Inc.
|
According to an engineering
web site
at the University of Buffalo, these Japanese companies produce SAPs: Nippon
Shokubai, Sanyo, Mitsubishi Petrochemical Company and Sumitomo Seika.
Superabsorbent diapers were introduced in Japan in 1983, and
are now widely used in plastic diapers globally. Ultra Pampers by Procter &
Gamble were the first diaper introduced in the United states to use
superabsorbent polymers.
The absorbency of the polymer in diapers is carefully
engineered to match the projected output of urine from a baby. SAPs designed
for maximum absorption can create gel blocks that prevent all of the urine from
reaching the diaper. Also, if the absorption rate of the diaper is slower than
the urination rate of the baby, leakage will occur.
Now SAPs are engineered for other
tasks, such as solidifying
waste waters and sludge.
Waste
Lock 770 from M
2 Polymer Technologies
has been engineered to absorb under pressure and has properties that make it
ideally suited for the absorption and solidification of low-level radioactive
waste and other types of waste sludges. It's approved for use at the nuclear
production
site
in Hanford, WA.
Conventional industrial absorbents include lime kiln dust,
Portland cement, dried corn cob, shredded newspaper, bentonite clay and saw
dust.
"In the case of radioactive waste, where loads must be
shipped long distances and landfill costs can reach $1000 per cubic yard or
more, the use of super absorbent polymer to prevent volume expansion is quickly
realized in cost saving," said Martin Matushek, vice president of M
2
Polymer Technologies of West Dundee, IL, in an
article
published in 2007.
Waste Lock polymers are based on polycarboxylate chemistry that provides a strong ion exchange affinity
for soluble metal ions.
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