Plutonium chemistry a boon for nuclear waste management

New insights into how the radioactive heavy metal bonds with other elements may pave the way for cleaner nuclear power, writes Joel Hooper.

Techniques for handling radioactive substances have come a long way since the 1950s.
Bettmann / Getty

Scientists at Florida State University have gained new insight into the chemistry of plutonium, breaking ground in the search for cleaner nuclear processes.

The radioactive heavy metal plutonium (Pu) has left a huge footprint on our society. Only five years after the element was discovered in 1940, a little over six kilograms of plutonium was at the heart of the atomic bomb that levelled the Japanese city of Nagasaki. Plutonium is also a key energy source in around one-third of nuclear power generated worldwide.

It’s also an extremely dangerous substance: not only is it radioactive, it’s also conventionally toxic like other heavy metals. So it’s critical that chemists find ways to manipulate it and clean it up in the event of a spill like the one that occurred in the 2011 Fukushima disaster.

However, plutonium is tough to manage because its chemistry, like that of other heavy elements towards the bottom of the periodic table, is incredibly complex. An element’s chemistry depends mainly on the number of electrons in orbit around the nucleus of the atom, and heavier elements have more of them. (Radioactivity, on the other hand, depends on the configuration of the protons and neutrons in the nucleus.) This complex chemistry makes plutonium more difficult to recover, process and purify than lighter metals such as iron or copper.

In their research, published this week in Nature Chemistry, the team at FSU, led by Professor Thomas Albrecht-Schmitt, showed that plutonium, surrounded by supporting organic molecules, can behave much like the lighter elements that chemists are more used to handling.

In this newly discovered plutonium compound, the team could observe that electrons were able to transfer between two neighbouring plutonium atoms, a phenomenon seen in lighter elements, but previously not observed with plutonium.

Chemists can often learn how the electrons in a chemical compound are behaving based on the colours that are produced. Albrecht-Schmitt said that the colour of their new material immediately grabbed their attention.

“Plutonium makes wild, vibrant colours,” he said. “It can be purple, it can be these beautiful pinks. It can be this super dark black-blue. This compound was brown, like a beautiful brown chocolate bar.”

“In order to develop materials that, say, trap plutonium,” Albrecht-Schmitt added, “you first have to understand at the most basic level, the electronic properties of plutonium.”

Understanding plutonium chemistry may pave the way for cleaner nuclear power with less toxic waste. David Clark, a leading chemist at the Los Alamos National Laboratory has written that a “zero effluent” nuclear facility using “molecularly engineered plutonium compounds and total recycle of environmentally benign designer solvents” may not be far away.

Joel Hooper is a senior research fellow at Monash University, in Melbourne, Australia.