US nuclear reactor breakthrough unravels plutonium oxide’s secrets at 3000 K

Scientists at the Argonne National Laboratory, which is part of the US Department of Energy, have made a significant discovery by studying how liquid plutonium oxide (PuO2) behaves at extremely high temperatures, up to 3,000 Kelvin.

This important research could greatly improve how safe and effective future nuclear reactors are designed. The need for this study came from the critical importance of knowing how nuclear fuel materials act in extreme conditions.

In 2014, Argonne scientists were able to measure the structure of molten uranium dioxide (UO2), which is a key part of nuclear fuel.

However, examining PuO2 was much more challenging because of safety issues and the complex nature of the material itself.

Innovative experimental technique

The research team used a novel technique where they suspended tiny samples of PuO2 in a stream of gas and heated them with a laser. “Samples of PuO2 measuring about 2 mm in diameter were levitated on a gas stream and then heated by a carbon dioxide laser beam until they melted,” stated the researchers in a press release.

“This allowed the team to measure the samples’ structure at temperatures as high as 3,000 K without risking sample contamination from container interactions.”

The findings of this study were notable. By heating the sample at different temperatures using various gas streams, researchers observed changes in the melt’s volatility and structure across different atmospheric conditions.

“We solved the structure of liquid plutonium oxide and found that some covalent bonding was indeed present,” said Argonne Senior Physicist Chris Benmore.

“We also discovered that the liquid structure was similar to cerium oxide, which can be used as a non-radioactive substitute.”

While researchers have used levitators to melt materials at very high temperatures before, using this method with nuclear fuel materials involved additional challenges, requiring a higher level of technical skill and thorough safety reviews.

Simulating electrons’ behavior

In addition to their experimental success, the research team utilized Argonne’s powerful supercomputers.

They developed machine learning models to simulate how electrons behave in the system, which aims to shed light on bonding mechanisms and safety issues when using mixed oxide fuels in future nuclear reactors .

Mark Williamson, the director of Argonne’s Chemical and Fuel Cycle Technologies division, pointed out the broader significance of their findings.

“The data from the combined set of experiments not only provides information of technological importance, it also provides insights into the fundamental behavior of actinide oxides at extreme temperatures,” asserted Williamson.

Special role of Argonne lab

At Argonne National Laboratory, scientists have access to specialized facilities and possess extensive expertise, which enabled them to tackle this complex challenge.

“Argonne is probably the only place in the world capable of performing this very difficult type of experiment,” highlighted Benmore.

The latest research represents a major step forward in creating safer and more efficient nuclear energy systems.

​“This has been a fantastic collaboration of experts, and it’s an excellent example of how we work together to continually improve nuclear energy systems,” concluded Williamson.