What is nuclear fusion and why it still can't help the climate crisis

The next leap of human civilization could be in the stars. More specifically in the domain of stellar energy: nuclear fusion.

Fusion, due to its potential to generate enormous amounts of clean energy, brings the hope that, in the future, nations will no longer depend on fossil fuels for energy generation.

The problem of the previous paragraph is in one word: future. Humanity cannot rely immediately — and considering the current technological stage, even in the medium term — on this energy source to deal with the ongoing climate crisis on Earth.

Nuclear fusion occurs when two hydrogen nuclei fuse together and form a helium atom. There is a caveat here: do not confuse fusion with nuclear fission, which is used in nuclear power plants and consists of, as the name says, bumping two atoms so that they “break”.

If o human being can “break”, so the path to merge should already be known, right?

Right. The problem is to put into practice and control, on Earth, the reactions that occur in stars.

Fusion is only possible when the particles are at very high temperatures — to the point of forming plasma, the fourth state of matter, an ionized gas— under high pressure. This is because the protons (present in the nuclei that one wants to collide) exert repulsion among themselves. To bring them together and fuse them, only under extreme conditions, such as millions of degrees Celsius inside a fusion reactor.

But when the union works and helium forms, large amounts of energy are produced, which, in turn, could serve the energy thirst of humanity.

Currently, we are already able to produce fusion, but there are a series of problems that prevent its use for production commercial energy.

“The biggest problem is that more energy is not generated than is consumed”, says Vinícius Njaim Duarte, a researcher at the Plasma Physics Laboratory at Princeton University, in the United States . In other words, the energy used to put the fusion reactors into operation is greater than the energy generated in the reaction.

In August of this year, from fusion, scientists were able to produce 10 quadrillion watts, at a point the size of a human hair, for 75 trillionths of a second. For this, they bombarded a hydrogen plate with more than a hundred lasers.

This specific initiative, however, has no energy purpose, warns Njaim Duarte. The objective of the Lawrence Livermore National Laboratory’s program, at the National Ignition Facility, in the USA, is military, in search of new weapons.

But, back to peaceful applications, another problem is the very little time. that researchers manage to maintain the reaction. For large-scale power generation, of course, it would be necessary for the process to be more durable.

In June this year, the Chinese reactor East (Experimental Advanced Superconducting Tokamak) announced that it had reached a record: maintain the plasma flow for 75 seconds at 120 million degrees Celsius.

Besides the matter of time, there is also the problem of the raw material of the plasma. Two isotopes of hydrogen are needed, deuterium and tritium.

Deuterium is an isotope widely available in Earth’s oceans. According to the Princeton researcher, the reservoir is virtually inexhaustible. But tritium practically doesn’t exist.

“There is no more tritium in nature, anywhere in the Universe”, says Gustavo Canal, a researcher at USP at the plasma physics laboratory. The element is radioactive and has a half-life (generally, the time it takes for the amount of the substance to decay by half) of only 10 years.

For the production of tritium, it is necessary to bombard lithium with neutrons, one more step for the production of energy from fusion.

“Very high”, “huge”, “millions”, “quadillions”, substances that don’t exist. The descriptions already give an idea of ​​the level of complexity of the process. And, with nuclear accidents that have marked the last decades, grandiloquent descriptions can also sound like a warning of risk.

But, in addition to the promise of clean energy, fusion brings with it the guarantee of safety, experts say.

Any problem in the process, contrary to what one might imagine from an experiment with so many superlatives, would only result in the interruption of the complex reaction.

TOKAMAK

Fusion is now often developed in machinery known as a tokamak. It is where, in a vacuum, heat and magnetic fields conduct the soup of deuterium and lithium, preventing the particles from colliding with the walls.

, have to collide with the walls. The energy contained in this shock is transformed into heat, which heats water, which in turn evaporates and turns turbines, which then generate electrical energy —mechanisms already used in thermoelectric plants.

There are other machines with different tokamak configurations, but the essence is the same.

The test, perhaps definitive, of the viability of fusion for energy production is almost ready, in France, thanks to a group of more than 30 countries that seek the path. “The way”, in Latin: Iter.

The colossal tokamak Iter, at a cost of about US$ 20 billion, has large ambitions: to be the first in which fusion produces more energy than it consumes and the first to work for long periods, two of the problems mentioned above.

A joint international work to carry out the project, which had beginning with Cold War plans of collaboration between the US and the Soviet Union, it ends up, in the current scenario, finding an echo in the universal effort of nations —which at least should happen— to contain the climate crisis.

Logically, the structure of a tokamak also needs to withstand the hurdle of nuclear fusion. And then another question comes in: the development of sufficiently resistant materials.

The hostility of the interior of a fusion reactor is compared, by Duarte, to a spacecraft re-entering the atmosphere. “The nose of the space shuttle is small and it only needs to withstand the bombardment of particles for a few seconds. The Iter has to withstand twice as much bombardment for hours, for years.”

And it doesn’t stop. Ouch. During fusion, instabilities occur that generate filaments at the edges of the plasma, the ELMs (Edge-Localized Mode). Something comparable would be solar eruptions, says Canal, who studies exactly this phenomenon and is looking for answers to the problem with a tokamak at USP.

If in a normal fusion process the bombardment inside the tokamak is already In the extreme, ELMs can take the situation to unimaginable levels.

“We are working at the limit of the materials we know,” says Canal. “During an ELM, the bombing value goes up exorbitantly, it is an order of magnitude above what the materials support.”

The Iter is already about 20% ready, and the first plasma should run through the device already at 2025, if the projections hold up.

Although all this technology still seems like a future Far away, the Princeton researcher points out that there is already enough private money being invested in the merger, which would suggest that stronger results may be closer than imagined. Among the investors in the merger are Google, Bill Gates and Jeff Bezos.

“Developed countries have realized that the future is the merger”, completes the scientist from USP, pointing out the state investments in the area. Canal also says that it is seeking, within Brazil, partnerships with companies to support the national fusion project.

“The domain of fusion will be a civilizing mark”, sums up Duarte, although clean energy, he ponders , it won’t be enough to solve all the problems in the world.

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