Special Polymers May Staunch Radioactive Leak

Japanese engineers stuffedsawdust, three garbage bags of shredded newspaper and superabsorbent polymer (SAP)into an eight-inch reactor containment crackin a desperate bid to stop radioactive water from leaking into the PacificOcean.

An earlier effort to fill the hole with concrete failed.

"We will continue to take all measures to ensure the safetyand to continue monitoring the surrounding environment around the PowerStation," the Tokyo Electric Power Co. said in an official statement regardingconditions at the Fukushima Daiichi Nuclear Power Station, which suffered thedouble whammy of an earthquake and a tsunami on March 11.

News reports indicated that the polymer mix was notinitially successful and that workers were stirring the mix in order toactivate the polymers.

Design News couldnot ascertain the supplier of the polymer or the specific formulation lastnight.

That information is critical because superabsorbent polymersare highly engineered to perform specific tasks. It seems logical that thepolymers came from a Japanese source, however, since there are major chemicalcompanies there that manufacture SAPs.

They were first developed in the 1960s by the U.S. Departmentof Agriculture. Their basic chemistry isfascinating.

The USDA was researching materials that could improve waterconservation in soils. USDA scientists designed a resin based on the graftingof acrylonitrile polymer onto the backbone of starch molecules. The hydrolyzedproduct produced water absorption greater than 400 times its weight.Conventional natural materials such as cotton and sponges can only absorb up to20 times their weight.

Japanese companies began independent research to developtheir 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 includedDow Chemical, Hercules, General Mills Chemical, DuPont, National Starch &Chemical and Enka (Akzo), according to a history by M² PolymerTechnologies Inc.

According to an engineering web siteat the University of Buffalo, these Japanese companies produce SAPs: NipponShokubai, Sanyo, Mitsubishi Petrochemical Company and Sumitomo Seika.

Superabsorbent diapers were introduced in Japan in 1983, andare now widely used in plastic diapers globally. Ultra Pampers by Procter &Gamble were the first diaper introduced in the United states to usesuperabsorbent polymers.

The absorbency of the polymer in diapers is carefullyengineered to match the projected output of urine from a baby. SAPs designedfor maximum absorption can create gel blocks that prevent all of the urine fromreaching the diaper. Also, if the absorption rate of the diaper is slower thanthe urination rate of the baby, leakage will occur.

Now SAPs are engineered for other tasks, such as solidifyingwaste waters and sludge.

WasteLock 770 from M² Polymer Technologieshas been engineered to absorb under pressure and has properties that make itideally suited for the absorption and solidification of low-level radioactivewaste and other types of waste sludges. It's approved for use at the nuclearproduction sitein Hanford, WA.

Conventional industrial absorbents include lime kiln dust,Portland cement, dried corn cob, shredded newspaper, bentonite clay and sawdust.

"In the case of radioactive waste, where loads must beshipped long distances and landfill costs can reach $1000 per cubic yard ormore, the use of super absorbent polymer to prevent volume expansion is quicklyrealized in cost saving," said Martin Matushek, vice president of M²Polymer Technologies of West Dundee, IL, in an articlepublished in 2007.

Waste Lock polymers are based on polycarboxylate chemistry that provides a strong ion exchange affinityfor soluble metal ions.