Feb
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New Answers to the Downside of Nuclear Energy
February 1, 2012 | Leave a Comment
Nuclear energy production as practiced since the cold war days leaves a lot of nasty, radioactive products behind. In the U.S. where regulatory leadership seeks to dismember the industry, discontinued efforts to recover and reuse worthwhile fuel, and has closed down the multi decade effort for a safe repository while no perceptible or credible effort is made to secure electrical base power production, a little good news is dearly welcome.
The news comes from technology research in efforts to contain the worst of fission reaction’s byproducts. Tina Nenoff at Sandia National Laboratories’ Surface and Interface Sciences Department and the collaborating team members have used metal-organic frameworks (MOFs) to capture and remove volatile radioactive gas from spent nuclear fuel to reduce radioactive waste.
Metal Oxide Framework from Sandia Labs. Click image for the largest view.
The Sandia team’s discovery could be applied to nuclear fuel reprocessing or to clean up nuclear reactor accidents. Other countries like France, Russia and India are reprocessing spent fuel, and have in some cases been doing so for decades, exploiting a characteristic of nuclear energy that used fuel can be reprocessed to recover fissile materials and provide fresh fuel for nuclear power plants.
Sandia’s MOF process reduces the volume of high-level wastes, a key concern of the Sandia researchers.
Nenoff starts the explanation, “The goal is to find a methodology for highly selective separations that result in less waste being interred. This is one of the first attempts to use a MOF for iodine capture.” Removing iodine, whose isotopes have a half-life of 16 million years, from spent fuel would cause a very different storage perspective.
The Sandia team studied known materials, including silver-loaded zeolite, a crystalline, porous mineral with regular pore openings, high surface area and high mechanical, thermal and chemical stability. Various zeolite frameworks can trap and remove iodine from a stream of spent nuclear fuel, but need silver added to work well.
Nenoff continues, “Silver attracts iodine to form silver iodide. The zeolite holds the silver in its pores and then reacts with iodine to trap silver iodide.” But silver is expensive and poses environmental problems. In response the team set out to engineer materials without silver that would work like zeolites but have higher capacity for the gas molecules. They explored why and how zeolite absorbs iodine, and then used the critical components discovered to find the best MOF, now named ZIF-8. “We investigated the structural properties on how they work and translated that into new and improved materials,” Nenoff said.
MOFs are crystalline, porous materials made where a metal center is bound to organic molecules by a mild self-assembly chemical synthesis process. The choices of metal and organic compounds will result in a very specific final framework.
The Sandia team’s research is based on a study searching for the best elements of the zeolite Mordenite because of its pores, high surface area, stability and chemical absorption. That information allowed the team to identify a MOF that can separate single iodine molecules from a stream of molecules. The MOF with the pore-trapped iodine gas inside can then be incorporated into glass waste for much safer long-term storage.
The Sandia effort is part of the Off-Gas Sigma Team, which began six years ago and is led by Oak Ridge National Laboratory. The project studies waste-form capture of volatile gasses associated with nuclear fuel reprocessing. Other team members, Pacific Northwest, Argonne and Idaho National Laboratories, are studying other volatile gases such as krypton, tritium and carbon.
The MOF and iodine research has driven two feature articles in the Journal of the American Chemical Society.
Dorina Sava said, “The most important thing we did was introduce a new class of materials to nuclear waste remediation.”
The most relevant information in publishing is another recent paper in Industrial & Engineering Chemistry Research showing a one-step process that incorporates MOFs with iodine in a low-temperature, glass waste form.
Nenoff says, “We have a volatile off-gas capture using a MOF and we have a durable waste form.” Nenoff and her colleagues are continuing their research into new and optimized MOFs for enhanced volatile gas separation and capture.
The Argonne National Lab’s collaborating Karena Chapman sums up with, “We’ve shown that MOFs have the capacity to capture and, more importantly, retain many times more iodine than current materials technologies.”
The national labs efforts are laudable, but the U.S. failure to pursue a program for recycling spent nuclear fuel has put the nation far behind other countries and represents a missed opportunity for investment, jobs, exports, profits and taxed earnings. The failure to enhance the nation’s energy security also fails to influence other nations to operate more safely and increases the risks of proliferating weapons instead of reprocessing fuel.
Perhaps with more views made possible with the Internet, the hysteria of the media elites and the political class pandering to the lowest level of public opinion shrinking, a little progress can be made – someday.
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