PNNL

A molecular model of a new MOF that selectively traps xenon, a gas that is released during reprocessing of nuclear fuel.

How can you capture an element that doesn’t react chemically? As part of a multi-institutional, international collaboration, PNNL’s Praveen Thallapally and team are investigating a new material that might help in nuclear fuel recycling and waste reduction by capturing xenon and krypton gases released during reprocessing. The current technology to remove these noble gases requires extremely low, energy-intensive temperatures, which is costly, and generates hazardous ozone.

The team is investigating metal-organic frameworks (MOFs) that could potentially trap xenon and krypton without cryogenic distillation. They used computer modeling to screen 125,000 MOFs for structures suited to capturing these gases so they could test the most promising ones. The one most selective for xenon had previously been synthesized and named SBMOF-1.

When tested in a PNNL lab to filter a gas mixture that simulated reprocessing conditions, SBMOF-1 showed a xenon adsorption capacity of 13.2 mmol Xe per kg, 20 percent and 275 percent higher, respectively, than the benchmark materials CC3 and Ni-MOF-74; it had a remarkable selectivity for xenon over krypton at ambient temperature, withstood repeated use without degrading, and even worked well at high humidity, retaining more than 85 percent of the amount of xenon as it did under dry conditions. Once the xenon was removed, the same material could capture krypton. By working at ambient temperature, the new material could save energy and make reprocessing cleaner and less expensive—reducing cost by as much as 40 percent. The reclaimed gases can also be used in commercial lighting and insulation markets.

Thallapally said, “This is a great example of computer-inspired material discovery. The computer simulation helped us screen a large number of MOFs, which is very difficult to do experimentally.” This collaboration between experimentalists and modelers from academia, industry, and fellow national labs was recently featured in Nature Communications.

Equipped with these new insights, the researchers can further explore SBMOF-1 and other MOFs for nuclear fuel recycling, which would both reduce nuclear waste and generate carbon-free electricity. These MOFs might also be able to capture other noble gases such as radon, which pools in some basements.

For more information, see the PNNL News Release.

PNNL Research Staff: Radha Motkuri, Jian Liu, Praveen Thallapally, and Debasis Banerjee