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Researchers advance in managing nuclear waste

There have been many recent advances in understanding the chemistry of nuclear wastes. These developments center around a phenomenon known as complexation, which describes the process that occurs when several molecules surround an atom and attach to it, building a bigger, more complex structure with different behaviors. In the following studies, several teams looked at special complexes created with heavy metal atoms at the center.

Attempts to contain meltdown at the Fukushima-Daiichi nuclear power plant in Japan due to last year’s tsunami involved dumping massive amounts of seawater onto damaged nuclear material to cool the fuel.

An article in the Proceedings of the National Academy of Sciences entitled "Uranyl peroxide enhanced nuclear fuel corrosion in seawater" focuses on the chemistry that occurs when seawater meets nuclear waste. Experiments were carried out in the lab to study the water-waste system. It was found that the radioactive nuclear material would irradiate the water, causing it to form a set of chemicals known as peroxides. These peroxides subsequently corrode the waste and form complexes with radioactive and toxic uranium. These complexes form together into large clusters containing as many as 60 uranium atoms.

The clusters were discovered to be incredibly long-lived. They pose a significant contamination threat since the highly-radioactive uranium complexes can persist and disperse throughout the environment. Such clusters were made in the lab for testing, and at the time of publication, had shown no sign of breaking down over the course of 294 days.

While flowing water may be used to contain radiation, we are now aware of the dangers of allowing stagnant water to interact with nuclear material, as was allowed to at the Fukushima-Daiichi site

An article in the Journal of the American Chemical Society puts complexation to good use in the "Capture of Volatile Iodine, a Gaseous Fission Product, by Zeolitic Imidazolate Framework-8." If handled properly, components of nuclear waste can be separated so that some of the elements can be disposed of and others cleaned up to reuse as fuel. One of the compounds which is most dangerous and difficult to handle is iodine, which easily escapes as a gas. One form of iodine doesn’t break down for millions of years and another type is incredibly hazardous to humans.

Current methods for capturing iodine include the use of silver in special structures, however this is costly and not entirely environmentally friendly. The latest development involves the use of a new material called "ZIF-8," which forms a chemical framework around iodine, thus preventing its release. The researchers not only showed that the material worked in principle, but proceeded to extrude the loose powder into pellets. These pellets are easier to handle and incredibly efficient at binding the iodine gas for easy containment and removal.

In cleaning up wastes to be used again, it’s also necessary to carefully isolate heavy metals known as actinides; this is often accomplished with chemicals known as extractants. A team of scientists spread across Europe were attempting to create modified extractants with increased ability to dissolve in water, when they made a fortuitous discovery outlined in their paper "Synthesis and Evaluation of Lipophilic BTBP Ligands for An/Ln Separation in Nuclear Waste Treatment," published in the European Journal of Organic Chemistry.

They made slight changes to extractant molecules in the hopes that the improved chemicals would mix better with water and wastes. Unexpectedly, the new compounds were actually less soluble in water. However, an unanticipated side effect was observed: When placed in some organic solvents, the extractants were remarkably more efficient at complexing the actinides while not interfering with other components.

With the current widespread use of nuclear power, the understanding from these studies is critical for taking care of the environment and keeping people safe from radioactive exposure. Scientists working independently around the world have increased our knowledge of how to handle nuclear accidents and improved our ability to recycle used nuclear material while minimizing the release of toxic wastes.

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