WHY DON’T WE HAVE NUCLEAR FUSION YET?

TEXT TANITA HECKING
ILLUSTRATION ANTON HALLMAN / SEPIA

—— Nuclear fusion has been talked about for decades as an inexhaustible and environmentally friendly energy source. What sounds so enticing in theory, however, has continued to fail in practice thus far. The following are five problems that nuclear fusion is still struggling with today.

HOW DOES IT WORK?

Nuclear fusion mimics the high-energy processes of the sun. Two tiny atomic nuclei of hydrogen fuse to become one larger atomic nucleus, releasing a neutron and a whole lot of energy in the form of heat, which could then be converted into electricity. In practice, the hydrogen isotopes of deuterium and tritium are meant to fuse together to form helium. One of the biggest challenges of nuclear fusion lies in the atomic nuclei themselves, which both have a positive charge and normally repel one another. Fusion only becomes possible if the hydrogen atoms can get close enough together that the attracting forces outweigh the repelling forces, and the two atoms can fuse. To achieve this, however, requires temperatures of several million degrees Celsius.

Why is it stuck?

1. THE PLASMA

For the atomic nuclei to fuse with one another, there must be a stable plasma in the vacuum vessel of the fusion reactor. Plasma describes the fourth state of matter along with liquid, solid and gas. To achieve a plasma state, gas is heated to the extreme until the atoms and electrons begin to move and separate from one another. However, the ability to maintain this sort of plasma at the scale necessary over weeks, much less months, has not yet been managed.

2. THE RAW MATERIALS

Nuclear fusion could be achieved using the hydrogen isotopes deuterium and tritium. While deuterium can be extracted from seawater, tritium only occurs in trace amounts in nature and must be secured by other means.

3. THE EQUIPMENT

The interior of the reactor is subject to a tremendous amount of heat of up to 150 million degrees, several times hotter than the interior of the sun. There is not yet any material known to us that can withstand such unimaginable heat over the long term.

4. THE BREEDING BLANKET

One solution could be to generate tritium with the help of what is known as a breeding blanket. Scientists describe this blanket as a shell that surrounds the plasma. When neutrons in this breeding blanket strike lithium molecules, tritium and helium are produced. However, no breeding blanket has ever been built or tested, nor has the concept been shown to work yet in computer simulations.

5. THE ENERGY

Fusing atoms together requires a lot of heat and tons of pressure. The problem is that producing both of these requires vast amounts of energy. So far, researchers haven’t been able to use nuclear fusion to generate more energy than the process consumes. Until this is the case, however, nuclear fusion will remain economically unviable.

THE ITER FUSION REACTOR

Researchers from 35 countries hope that the ITER Fusion Reactor will bring them one step closer to nuclear fusion. The reactor has been under construction in Saint-Paul-lès-Durance, France, since 2007. ITER received the first component for the vacuum vessel just this March. The reactor should be ready by early 2025 and it will generate the first plasma by late 2025. Yet several more decades may pass before nuclear fusion becomes a reality. Many of the processes involved simply don’t work yet, not even in theory.

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