Nuclear fusion is a reaction that has been known for more than a century, but little money has been invested in research on fusion reactors. According to Principal Scientist Tuomas Tala from the VTT Technical Research Centre of Finland, quick profits are easier to make by investing in conventional forms of energy.
“The war in Ukraine probably costs as much in a matter of days as has ever been spent on fusion research.”
Over the past few years, the situation has changed as a result of the climate and energy crisis. Fusion technology is rapidly being developed in Europe, the United States and China.
“In the last few years, risk investors have also joined in,” Tala says.
That is a good thing. Tala believes fusion energy would be the best way to replace fossil fuels and nuclear fission as a primary source of energy. Primary energy sources encompass forms of stable power generation that are not dependent on, for example, weather conditions.
No nuclear disasters, no waste problems
The nuclear reactors currently used in energy production are based on nuclear fission, where heavy elements such as uranium are split. The process generates nuclear waste, which is fatally radioactive for as many as 100,000 years. Should an accident occur in a reactor, the consequences can be catastrophic.
In nuclear fusion, elements are fused together. As fuel, fusion power plants use two isotopes of hydrogen, deuterium and tritium. The first can be obtained from seawater. The second can possibly be produced, as a by-product of the fusion reaction, from lithium.
When the different hydrogen isotopes are fused together, they transform into helium. As the mass of helium is smaller than that of the two hydrogen isotopes, the reaction releases a great deal of energy.
“Helium is also quite a valuable gas, which can be recovered and sold,” Tala says.
Nuclear fusion also generates radioactive waste, but it is not nearly as active as the waste from fission plants. In addition, most of the radioactivity dissipates in a few decades.
And accidents in fusion reactors do not result in nuclear disasters. The reaction simply stops.
Researchers are creating stars on Earth – not an easy task
For a fusion reaction to be initiated, the elements must be sufficiently hot and close to each other for a sufficiently long time. The longer the plasma remains confined, the more likely it is for the hydrogen atoms to collide and fuse into helium.
It is a fusion reaction that makes the sun blaze. In fact, fusion researchers are creating miniature stars in their laboratories.
“Thanks to its large size, keeping the elements confined is easy in the sun. We are trying to do the same in the laboratory within the space of a few hundred cubic metres,” Tala says.
Fusion reactors are equipped with the world’s strongest magnets, which are used to hold together plasma heated to as much as 100 million degrees. In the current reactors, the plasma can be confined for roughly a second at the most.
The heat generates turbulence, which makes it increasingly difficult to sustain the reaction.
“Increasing heat increases turbulence, hampering confinement. I investigate the minimisation of turbulence,” Tala says.
A problem: radioactive hydrogen trapped in the reactor
At the University of Helsinki’s Kumpula Campus, researchers are investigating which materials are best suited to the extreme conditions of a fusion reactor. At the moment, the most popular option is tungsten, which is used, for example, in the ITER reactor being built in France.
“But that doesn’t mean that tungsten is the best option. It may be that something more appropriate will be identified for the subsequent reactor,” says University Researcher Kenichiro Mizohata from the Department of Physics.
Tritium, one of the two fuels of fusion reactors, is radioactive – not to the same degree as the uranium used in nuclear fission, but radioactive nonetheless. This poses problems for the materials used. The magnets confine the fuel, but the hydrogen emitted from the plasma is stored, or trapped, in parts of the reactor.
“If the reactor stores a lot of tritium, it will become highly radioactive. However, for the most part this activity will dissipate in a few decades,” Mizohata explains.
Like tungsten, only better?
The problem with tungsten is that radiation damages its atomic structure. Once the material is damaged, the hydrogen becomes even more easily trapped in it. With the help of a particle accelerator, Mizohata’s research group is currently investigating material mixtures which have the useful properties of tungsten that would not be as easily damaged by radiation as tungsten is.
In any case, all materials store a certain amount of hydrogen. This is why the removal of hydrogen from materials is also studied at the Accelerator Laboratory.
“One new insight is isotope exchange. We are driving into the material a non-radioactive isotope of hydrogen, which kicks out the radioactive one.”
Fusion power in the 2030s
Fusion reactors are not yet used for energy production, because the maintenance of existing reactors consumes more energy than it produces. In December, American researchers announced that they had managed, for the first time ever, to generate a fusion reactor with laser beams that produced more energy than was consumed by the lasers maintaining it.
“To make it commercially viable, the energy output must be probably 30 times greater than what the fusion reactor consumes,” Tuomas Tala notes.
He believes that fusion power will be released into the grid in sample form in the United States in the 2030s. It may take longer to achieve a 30-fold gain factor.