Interview with Isabel García Cortés, who holds a doctor in physics and works as a researcher at fusion laboratory of Spain’s energy, environment and technology research center, CIEMAT
What is nuclear fusion and how does it differ from nuclear fission at nuclear power plants?
Both nuclear fission and nuclear fusion are energies that come from the nucleus of atoms, which is why we call them ‘nuclear.’ They differ in that fusion obtains energy through the union of two nuclei, while fission involves the splitting of a heavy nucleus into two lighter nuclei.
The fission of a nucleus of a heavy element of the periodic table releases a huge amount of energy, as we know from the nuclear fission power plants across the planet. However, nuclear fusion consists of the reverse process, i.e., the union of two nuclei of light elements to obtain a heavier element, which also releases a large amount of energy.
The fusion process is the driving force of all stars in the universe. The Sun, for instance, produces so much energy because fusion reactions are continuously taking place there. The heat that reaches the Earth and fuels life here arises from the fusion of nuclei of hydrogen atoms forming helium atoms. Fusion research aims to simulate the Sun’s processes in a controlled manner on Earth for use as a new energy source. This could supply an answer to humanity’s growing demand for energy consumption.
Seventy years ago, when the search for this energy source began, researchers looked precisely at the processes in stars. However, something that seems simple in stars turns out to be one of the biggest challenges we face today.
What are the pros and cons of nuclear fusion versus nuclear fission?
I should say the main drawback of fusion versus fission is that we don’t have it up and running yet. There are no fusion reactors supplying power like fission power plants do. It’s also much more technologically challenging. Given what we know today, a fusion power plant will be far more technically complex than a fission power plant.
But fusion also has many things going for it. To begin with, it’s fueled by hydrogen, which is easily found in nature. On the face of it, we would have inexhaustible fuel. Moreover, nuclear fusion doesn’t involve chain reactions. In magnetic confinement reactors, for example, processes continue only if there is a magnetic bottle that keeps them stable and away from material surfaces. If we switch off the magnetic field, the reactions stop and the fuel cools down and ends up as a harmless hydrogen gas. There are no chain reactions, unlike fission, where the process can be hard to control.
Finally, the waste generated by nuclear fusion is of medium or low activity, unlike the waste from fission power plants, which lasts for hundreds or even thousands of years. However, let’s not forget that fusion energy is also nuclear. Therefore, it will require waste supervision and management following the regulations established by the competent nuclear authorities.
How does a fusion reactor work?
In a magnetic confinement fusion reactor there are several basic procedures. The first procedure involves the fusion process itself, in the fuel container. In our case the container resembles a large hollow doughnut where a vacuum forms to ensure that no other element that is in the air enters and thus only the hydrogen is acted on.
Once the vacuum arises in our chamber, we need the fuel. We introduce hydrogen in gaseous form. We will need to heat it so that the nuclei will fuse. For this to happen, the fuel needs to be at hundreds of millions of degrees. We must raise the temperature of the gas in the chamber until it is no longer a neutral gas, in which the electrons are bound to the protons and the nucleus. Instead, the electrons (negatively charged) detach from their positively charged nuclei and form a ‘plasma.’ This plasma is our fuel. Plasma, an ionized gas at extremely high temperature, is the fourth state of matter.
Finally, we set up magnets that generate a magnetic ‘bottle’ that confines the plasma (as an ionized gas, the particles will follow the magnetic field lines). This prevents the plasma from approaching the walls. These steps require the use of sophisticated technology in the latest generation reactors. For example, we use superconducting coils to achieve stronger magnetic fields and more effectively trap all the particles and keep them away from the container walls. The development of superconducting coils is one of the scientific breakthroughs that have come to the aid of fusion technology.
Once all this is set in motion and continues long enough, the particles begin to coalesce and the reactions begin. In addition to supplying power to the grid, the heat given off by the process can heat the plasma itself. The heating systems needed to start the reactions become unnecessary.
There are many experiments underway that help us toward an advanced understanding of what fusion reactors could be like, but the fact is that there is still no prototype fusion reactor in operation. The ITER (International Thermonuclear Experimental Reactor) aims to prove that such a reactor can supply enough energy to counteract the energy expenditure involved in igniting fusion reactions. This is an international project that in 10 years’ time should give answers to this and many other questions on the road to the design of a commercially viable reactor.
What is ITER? What is it for?
ITER is the big dream on the road to fusion. When I started in fusion research many years ago, there was already talk of ITER. The project has evolved from a simple and unambitious machine to what it is today: a large-scale project that brings together myriad systems that push the limits of technology.
It has had its ups and downs, in step with the cost of fossil fuels. Fusion energy research really took off with the oil crisis of the 1970s. Then, with oil becoming cheap, investment in fusion petered out and research has progressed more slowly. The same has happened with projects such as ITER.
ITER is currently well advanced, however. It’s an international partnership of 35 countries (the 27 countries of the European Union, Switzerland, the United Kingdom, China, India, Japan, South Korea, Russia and the United States) that seeks to answer the big questions of fusion, such as whether controlled fusion is viable as a stable energy source. The fact is, we know that fusion reactions do happen, but we also need to know if we can control them in a stable and predictable way. We cannot have plasma instabilities in the many systems needed for the plant as this would fail to ensure the desired continuity in the power supply.
ITER is not a commercially viable reactor, but it is necessary to understand and decide on a safe pathway to a fusion power plant.
What are the main difficulties in creating a fusion reactor?
There are many challenges. For many of them, we won’t have an answer until ITER is operational.
For example, I said earlier that we use hydrogen. But in reality hydrogen comprises three different elements: hydrogen, deuterium and tritium. Hydrogen has no neutrons in its nucleus, while deuterium has one and tritium has two. The most effective reactions, which would lead us to have energy more easily, are those of deuterium and tritium. We can easily get deuterium from seawater, but tritium is much harder to come by. It’s half-life is only nine years, and it must be produced initially in a fission power plant. We need to have it available to start fusion reactions in ITER and future reactors.
During reactions, a tritium atom plus a deuterium atom results in a helium atom plus a high-energy neutron, which gives up its energy in a lithium mantle on the first wall of the vessel. The lithium in the mantle, reacting with the neutron, yields tritium again, which we will need to be capture and redirect back into the plasma to continue fueling the fusion reactions. Therefore, for fusion to be commercially workable, tritium must be recycled. And the process of capturing that neutron in the special materials of the first reactor wall is what we will put to the test in ITER.
Another challenge lies in the materials themselves. How will the materials react to such a heavy flow of neutrons? And not only in that first wall, but also in the structures and systems next to the reactor, which the neutrons also pass through. We must be sure that neither the first wall, which is critical in the recovery of tritium, nor the structure, nor the various basic diagnostics in plasma control, lose their properties.
Yet another challenge is the development of new special materials that can withstand the conditions of future fusion reactors. The key to this is the large particle accelerator IFMIF-DONES to be built in Granada. This is a project promoted and developed by CIEMAT in partnership with the University of Granada. The accelerator will serve as a test bed for developing the best materials for future fusion plants.
But there are still a lot of unknowns.
You are a researcher at CIEMAT’s fusion lab. What are you looking into there?
The flagship of our lab is the TJ-II fusion device at CIEMAT’s Moncloa headquarters. It has been producing plasmas since the 1990s. The device is part of the European project for developing fusion as an energy source. We work with other international institutions to try to answer questions about magnetic confinement. For instance, how do different magnetic setups affect plasma confinement?
Building machines to investigate plasma under fusion conditions and their operation is expensive. Investment in this branch of science is therefore centralized at the labs that house these devices. In Spain, for example, the leading center is CIEMAT, because it houses the TJ-II. In addition, each device has unique features and specializes in certain lines of research. The intention is that all the knowledge will converge toward the development of ultramodern devices.
At our lab, besides the research using TJ-II, several successful working groups have appeared. Some of our researchers–all women, incidentally–are working with JET in the UK, for instance. It’s the only device capable of simulating reactor conditions. They have conducted recent experiments and their results will have profound impact on the development of ITER and future machines.
We are a multidisciplinary group. Therefore, we have a strong capability to address technological developments related to fusion energy. For example, CIEMAT is coordinating the design of several diagnostic and control systems for ITER that will be key to its start-up and scientific output. Another key group at our lab is developing the IFMIF-DONES infrastructure, which addresses the challenge of fusion reactor materials.
In my own group, we are looking at an alternative method to feed the plasma using solid hydrogen pellets of one millimeter in diameter at cryogenic temperature (4 degrees Kelvin), which we inject at high speed to easily reach the center of the plasma, where the best conditions for fusion reactions occur. Using TJ-II we have seen that this way of introducing the fuel into the plasma extends the operational range of the device, with better plasma quality and enhanced confinement. We have achieved records in these parameters. It’s a partnership between three labs in Spain, Germany and Japan. The results have an impact on the development of these systems for future reactors.
What role will nuclear fusion play in future in the international energy mix?
There are still hurdles to overcome, which is why most of the investment in fusion energy research is government-funded. If there were absolute certainty that fusion power plants are a viable business, in fact, their development and construction would already be in the hands of the leading power utilities.
But I believe human beings are used to overcome challenges that may have seemed impossible for generations. So I do believe fusion power plants will be a reality in the not too distant future.
What role will fusion play? Fusion will play a role, but it will not solve the whole energy problem. Humankind is a voracious consumer of energy, and I am sure we will have to make use of all sources available to us.
We should be far more careful with the environment and try to scale down our dependence on fossil fuels. The future of the energy mix should be geared toward renewables plus nuclear. This is essential to make progress in the decarbonization of the planet.
What will the future look like? Given the geopolitical changes we’re seeing lately, it’s hard to imagine. These changes have a huge influence on countries’ energy policymaking. At one time it may be a priority to close down nuclear power plants in Germany. Yet, at another time, in the face of the impossibility of importing gas to produce energy, nuclear power could be a lifeline.
Some sociological studies suggest that fusion power will replace fission power as resources run out. But this, as I said earlier, is part of the long term view, and is hard to foresee.
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