Research Could Save Money and Reform Nuclear Waste ReprocessingSiobhan Treacy | November 01, 2017
Rutgers-New Brunswick scientists have been seeking a better way to capture radioactive iodides in spent nuclear reactor fuel. They have developed an extremely efficient “molecular trap” that can be recycled and reused.
The trap is a small, porous super-sponge. The internal surface area of one gram of this material could stretch out to cover five 84 x 50 ft. basketball courts, or 23,500 square feet. Once caught inside, radioactive iodides will remain trapped for eons.
"This type of material has tremendous potential because of its high porosity," said Jing Li, distinguished professor in the Department of Chemistry and Chemical Biology at Rutgers University-New Brunswick. "It has far more space than a sponge and it can trap lots of stuff."
Reprocessing means separating spent nuclear reactor fuel into materials that may be recycled for use in new nuclear fuel or discarded as waste, according to the U.S. Nuclear Regulatory Commission. The U.S. has no commercial reprocessing facilities at the moment, but commercial facilities are operating in other countries.
When spent fuel is reprocessed, radioactive molecular iodine and organic iodide gases that pose health and environmental risks must be captured and sequestered. The long-lived gases are hard to capture and can leak into the environment, according to the Rutgers study.
Solid adsorbents — like silver-infused silica, alumina and zeolites — can capture iodides, but their low uptake capacity and poor recyclability to make them inefficient and costly, according to Li.
Because of this, Rutgers and other researchers developed a “molecular trap” made of a highly porous metal-organic framework. Its performance exceeds the standard set by nuclear industry rules, which require waste reprocessing plants to remove more than 99.9% of radioactive iodides from spent nuclear fuel rods.
It also far outperforms all current industrial materials in adsorbing, or binding to, radioactive organic iodides. For example, its ability to adsorb methyl iodide at 302˚ F exceeds that of a benchmark industrial product by more than 340 percent.
Another benefit of this molecular trap is that captured methyl iodide can be removed from metal-organic frameworks, enabling their recycling and reuse. This is not possible with the current industrial product, from which adsorbent must be sequestered along with captured radioactive iodides.
The metal-organic framework is also cheaper than existing products because it doesn’t use silver or other precious metals, and is robust and able to handle harsh reprocessing conditions like high temperatures, high acidity and high humidity.
"We're off to a very good start and we'd like to make improvements," Li said. "Eventually, we hope it can be commercialized."
The paper on this research was published in Nature Communications.