Game changing new method to increase production of nuclear fusion fuel

If scientists could create a sustained nuclear fusion reaction it would revolutionise the way we produce energy – day or night, rain or shine, sans carbon emissions.

Among the myriad challenges facing physicists trying to make it a reality is the process of isolating lithium-6, an isotope essential to producing the fuel which is used in nuclear fusion.

Producing it has conventionally been done using a process which requires toxic liquid mercury, which was banned in the US in 1963 because of pollution concerns.

Now researchers have developed a new, mercury-free method that is just as effective.

“This is a step towards addressing a major roadblock to nuclear [fusion] energy,” says chemist and senior author of a paper describing the breakthrough, Sarbajit Banerjee of Switzerland’s ETH Zürich and Texas A&M University in the US.

“Lithium-6 is a critical material for the renaissance of nuclear energy, and this method could represent a viable approach to isotope separation.”

In nature, lithium exists as 2 stable isotopes: lithium-6 and lithium-7. Both have 3 protons in their nucleus but contain different numbers of neutrons (3 and 4, respectively).

Lithium-7 is much more abundant, making up between 92.2-98.1% of all lithium on Earth, so the much scarcer lithium-6 must be “enriched” (isolated).

But almost all lithium-6 used in US research has been sourced from a diminishing stockpile at Oak Ridge National Laboratory in Tennessee, which was produced before 1963.  

There has been an urgent need to develop a safe new way to enrich lithium-6 for nuclear fusion research.

The new method was discovered by researchers developing membranes for cleaning “produced water” – groundwater brought to the surface during oil and gas drilling.

The membrane is made of a material called zeta-vanadium oxide, a lab-synthesised compound.

“We saw that [zeta-vanadium oxide] could extract lithium quite selectively,” says Banerjee.

“That led us to wonder whether this material might also have some selectivity for the 6-lithium isotope.”

Further experiments revealed that it did.

They found that a single cycle enriched lithium-6 by 5.7%, so the process must be repeated 25 times to produce fusion-grade lithium.

Repeating the process 45 times results in 90% lithium-6.

“This level of enrichment is very competitive with the [old] process, without the mercury,” says co-first author of the paper, Andrew Ezazi of Texas A&M.

“Of course, we’re not doing industrial production yet, and there are some engineering problems to overcome … but within a bunch of flow cycles, you can get fusion-grade lithium quite cheap.”

Nuclear fusion reactors mimic the process powering the centre of every star.

It involves smashing together 2 isotopes of hydrogen, deuterium and tritium, at millions of degrees Celsius, to produce 2 helium atoms, a neutron, and a massive amount of energy in the form of heat and light. 

Tritium is extremely rare on Earth, only occurring in the atmosphere in trace amounts, and must be artificially produced by irradiating lithium-6.

“I think there’s a lot of interest in nuclear fusion as the ultimate solution for clean energy,” says Banerjee.

“We’re hoping to get some support to build this into a practicable solution.”

The paper is published in the journal Chem.