New material may make nuclear fuel recycling cleaner, cheaper

Scientists, including one of Indian-origin, have found a new material that may help recycle and reduce wastage of nuclear fuels as well as save energy, making the reprocessing of radioactive materials cleaner and less expensive.
Conventional technologies to remove these radioactive gases operate at extremely low, energy-intensive temperatures.
By working at ambient temperature, the new material - known as metal-organic frameworks - can save energy, make reprocessing cleaner and less expensive. The reclaimed materials can also be reused commercially.
"This is a great example of computer-inspired material discovery," said Praveen Thallapally of the US Department of Energy's Pacific Northwest National Laboratory.

"Usually the experimental results are more realistic than computational ones. This time, the computer modeling showed us something the experiments weren't telling us," he said.
Recycling nuclear fuel can reuse uranium and plutonium - the majority of the used fuel - that would otherwise be destined for waste.

Researchers are exploring technologies that enable safe, efficient and reliable recycling of nuclear fuel.
They are studying materials to replace costly, inefficient recycling steps. One important step is collecting radioactive gases xenon and krypton, which arise during reprocessing.
To capture xenon and krypton, conventional technologies use cryogenic methods in which entire gas streams are brought to a temperature far below where water freezes - such methods are energy intensive and expensive.

Thallapally, working with Maciej Haranczyk and Berend Smit of Lawrence Berkeley National Laboratory, has been studying materials called metal-organic frameworks, also known as MOFs, that could potentially trap xenon and krypton without having to use cryogenics.
These materials have tiny pores inside, so small that often only a single molecule can fit inside each pore.
When one gas species has a higher affinity for the pore walls than other gas species, metal-organic frameworks can be used to separate gaseous mixtures by selectively adsorbing.
To find the best MOF for xenon and krypton separation, computational chemists screened 125,000 possible MOFs for their ability to trap the gases.

The team's models identified the MOF that trapped xenon most selectively and had a pore size close to the size of a xenon atom - SBMOF-1.
After optimising the preparation of SBMOF-1, researchers tested the material by running a mixture of gases through it - including a non-radioactive form of xenon and krypton - and measuring what came out the other end.
Oxygen, helium, nitrogen, krypton, and carbon dioxide all beat xenon out. This indicated that xenon becomes trapped within SBMOF-1's pores until the gas saturates the material.
The researchers will explore SBMOF-1 and other MOFs further for nuclear fuel recycling.

The research appears in the journal Nature Communications.