Bring the Sun to Earth

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At about 150 million kilometers from us there is a large and very powerful nuclear fusion power plant: the Sun. Without our star we could not imagine such a powerful source of energy, simply because we would not exist and even this article would not exist. The Sun is about 4.57 billion years old and has made the formation of life on our planet possible. It is a formidable source of energy and for this reason, for decades, researchers would like to imitate its mechanisms, creating nuclear fusion reactors on Earth: small suns that could solve most of our problems for the production of clean energy.

The challenge is scientifically and technically enormous, but despite the efforts of researchers and investments of several billion euros, for now it has proved unsuccessful. A new series of progress has now prompted some research groups to be more optimistic, contemplating the possibility of creating a first fusion power plant within twenty years. However, their statements do not convince other experts, who are very skeptical about this eventuality and believe that the production of energy from renewable sources – such as sunlight and wind – may be the only option that can really be used to reduce polluting emissions and consequently reduce the effects of global warming.

Today's nuclear power plants
Nuclear energy has been part of our existence for over half a century. Among the first to build a functioning reactor was the Italian physicist Enrico Fermi, who at the end of 1942 produced a demonstration model in the United States, illustrating the great potential of the new system. Since then, nuclear power plant technologies have evolved considerably, while maintaining the principle underlying their operation unchanged: fission.

In a nuclear fission reaction, the nuclei of heavy atoms (with a high atomic number) such as plutonium 239 or uranium 235 are induced to break, resulting in the production of nuclei with lower atomic numbers. A large amount of energy is released in the process, which in nuclear power plants is used to transform high-pressure water into steam, which then turns turbines to which generators are connected to produce electricity. However, the system implies the production of highly hazardous waste materials, the so-called "radioactive waste", which must be carefully preserved and isolated from the surrounding environment, to avoid contamination.

Nuclear Fission (Zanichelli)

Today there are about 450 nuclear fission reactors in the world, distributed in 31 countries: the United States is the country with the largest number of reactors (104), followed by France (58) and Japan (51). In Italy there were four, then closed following the referendums of 1987 which effectively prevented the construction of new plants and the maintenance of those already active. The referendum came after the Three Mile Island incident in the United States and Chernobyl in the Ukraine.

The fission plants are safe, and the new generation ones adopt additional systems to minimize the risk of damage to the reactors, which could lead to uncontrolled reactions and contamination. The next generation reactors, in the design phase, could be even safer and more efficient, but they would still involve the production of radioactive waste to be reckoned with. For this reason, researchers have been trying for decades to construct an alternative reactor to fission ones, which works with the same principle as what keeps the Sun going: nuclear fusion.

Nuclear fusion
Nuclear fusion is the opposite of fission: instead of breaking up heavy nuclei into smaller fragments, releasing energy, it combines light nuclei (like hydrogen) to obtain heavier ones. The process leads to the formation of new nuclei whose mass is less than the sum of the masses of those of departure: what is missing is emitted as energy in the form of gamma rays, highly energetic waves that can be exploited to produce energy.

The process we have described (with enormous simplifications) is rather linear, but very difficult to reproduce artificially on Earth. The nuclei of the atoms tend to repel each other (electric repulsion) and therefore serve temperatures in the order of several million ° C to tame them by transforming them into plasma and convince them to join together, through the use of very powerful magnets that contain the whole . In nature this mechanism occurs continuously in the stars, including the Sun, which can be considered real nuclear fusion generators.

To date, researchers have failed to implement a system that keeps the phenomenon under control for more than a few seconds, thus missing the possibility of exploiting it to produce electricity. An uncontrolled reaction is produced with the explosions of thermonuclear bombs, but it would not be a highly recommendable or minimally viable solution for the production of electricity.

The difficulties are many, starting with the system for containing the plasma at millions of degrees, produced by the fusion of the hydrogen nuclei. The most explored solution involves the use of large magnets to create a magnetic field that contains it, but to feed them huge amounts of electrical energy are needed, slightly less than those produced by the same fusion. Other researchers are considering the possibility of using simpler elements to melt, such as deuterium and tritium, in order to make reactor management less complicated.

The main advantage of nuclear fusion comes from the production of smaller and easier to handle radioactive waste than fission reactors, with much lower operating costs. The waste product of hydrogen fusion is tritium, an isotope whose radioactivity cannot overcome human skin, thus constituting a low risk to health in the event of accidental contamination. The tritium also decays rapidly, so it would gradually become less radioactive, in times comparable to those of the life of the fusion plants themselves.

A hypothetical nuclear fusion power plant would also have the advantage of not producing polluting gases and greenhouse gases, which contribute to global warming. The most used power plants today burn fossil fuels, such as gas and coal, releasing enormous amounts of carbon dioxide into the atmosphere that prevent the Earth from dispersing some of the heat received from the Sun. This is causing an increase in the global average temperature, with consequences for whole ecosystems and for our very existence, which could be mitigated through the use of "clean" energy sources.

ITER
The most important project in the field of nuclear fusion research to produce electricity is called ITER. It is the fruit of a collaboration between 35 countries working to build a first experimental reactor in Cadarache, in the south of France. The consortium includes the European Union, the United States, India, Japan, South Korea and Russia.

In these years, ITER has suffered numerous delays and has requested investments of almost 13 billion euros. In the course of this year the construction of some buildings for the electrical control and of the magnets was completed, and the structure was built that will be used to build the cooling tower for the process water, to be completed within a couple of years .

Building ITER buildings (iter.org)

ITER designers believe that by the end of 2025 the plant could be used to produce plasma, but several observers are skeptical about the possibility that this could happen in such tight times. At the moment there are no precise estimates of when other technical obstacles could be overcome to try to produce energy with the new reactor. The shared hypothesis is that a demonstration fusion plant based on ITER research will not be ready before 2050.

JET
The largest and most active experiment on nuclear fusion is always found in Europe and is called JET (Joint European Torus). The plant was built in Oxfordshire, in the United Kingdom, and is the result of an international collaboration that began in the 1970s and that would later form the basis for ITER. The European Union has financed the project until 2020, but it is not clear what will become of JET after that date, also because of the half there could be some complications due to Brexit (which could also concern ITER). Meanwhile, the British government has announced a € 255 million loan to design a fusion plant by 2040.

Tokamak
The experiments conducted in these decades have allowed us to study and perfect a large donut-shaped experimental machine (toroidal) called Tokamak. Inside it is produced the vacuum and the intense magnetic field necessary to isolate the plasma, so that it does not come into contact with the walls of the donut. Research indicates that in this way conditions can be created for thermonuclear fusion in a controlled way, so that it can be exploited to produce thermal energy to be transformed into electricity. The problem is that the Tokamak is a big greedy of electric energy and it is therefore to demonstrate its ability to produce more than is necessary to make it work.

In the UK the approach has been partially revised by making a version of the Tokamak that looks more like an apple than a donut. This spherical Tokamak can be smaller and therefore more practical for building smaller power plants in cities. Generally speaking, the closer a power plant is to where energy is consumed, the better: there are less costs for energy transport, fewer power lines to be built and fewer blackouts due to breakages along the line.

Creative fusion
ITER and JET are of course not the only projects underway for nuclear fusion research. Several countries are funding their own initiatives to explore alternative systems to the Tokamak or to improve their efficiency. One of the projects that concerns us directly is called the Divertor Tokamak Test (DTT) and was proposed by the National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA) and by several other Italian research centers, including 'National Institute of Nuclear Physics.

In September, the European Investment Bank confirmed the allocation of 250 million euros to set up the laboratories that will be used by DTT, and which will be built in Frascati, in the province of Rome. The project was approved by EUROfusion, the European consortium that deals with developing technologies for nuclear fusion.

DTT aims to study the best way to make a fun within a Tokamak. The divertor is the inner part of the reactor where the plasma is diverted that manages to escape the large magnetic containment field: the particles in flight could damage the walls of the Tokamak and therefore other magnetic fields must be used to make them come into contact with only some parts of the inner lining – that is the divertor – treated so as to withstand high temperatures and to be able to dissipate heat and dispose of other reaction residues.

Traditionally, research on nuclear fusion for civil purposes has been carried out by research centers with public funds, given the large amounts of money needed to design and build experimental facilities. However, the advancement of some technologies, the reduction in the size of the reactors and the prospect of producing large revenues with a functioning system have meant that in recent years some private companies have started their own projects, or funded research institutions.

California-based TAE Technologies has received funding from several private companies, including Google, and has among its objectives the construction of small and cheaper reactors. Its researchers have long explored the possibility of using elements such as hydrogen and boron for the reaction in a special reactor (CBFR) which, heating the gas, leads to the shape of two plasma rings, then fused and held together by other particle beams neutral, so as to make the reaction last and reduce the problems related to the management of magnetic fields.

Commonwealth Fusion Systems is another private company set up by some former researchers at the Massachusetts Institute of Technology (MIT). Their approach is more orthodox and always linked to the Tokamak concept, but concentrated on the construction of more efficient superconducting magnets, which can simplify plasma containment.

There are also those who are working on alternative systems, such as the Canadian company General Fusion, which says it wants to build spherical reactors of small dimensions, in which to pump liquid metal so as to "make it produce a vortex", in which it is then injected. of plasma (always with the system to contain it magnetically). Around the sphere there is a complex of pistons that are activated all together to exert a strong pressure and bring the plasma to the conditions of the fusion.

The heat produced by the reaction is transferred to the liquid metal, which in turn evaporates water which activates steam turbines. The process is repeated over and over, a bit like in a diesel engine. According to the designers, General Fusion could build a first functioning reactor within five years, and this is also why the company received funding from several entrepreneurs, including Jeff Bezos, Amazon's CEO.

The problem of problems
The problem, the biggest of all, is that at the moment no satisfactory energy balance has been reached in any experiment. Put simply: in fusion tests, more energy is used than is then produced by the process. Researchers and experts agree that it is only a matter of time, and of scale, to arrive at some more encouraging results. Research in the sector, however, requires billions of dollars in investments and the solution of international consortia involves some slowdown, for simple diplomatic reasons and of opportunism on the part of the single participating states, which understandably try to have a return on investment by encouraging research and induced within their borders.

Rethinking fission
The most critical, on the other hand, believe that excessive interest in fusion distracts attention from fission, that is, from the system we already use today in nuclear power plants, and from opportunities to improve it by making it safer and with the production of less waste. Bill Gates, the former head of Microsoft and one of the richest people in the world, thinks that the most viable solution to have energy and reduce carbon dioxide emissions passes through new-generation fission nuclear power plants.

Through its foundation, Gates has invested hundreds of millions of dollars in TerraPower, an initiative to design new reactors smaller than traditional ones, which use depleted uranium and whose waste can be used for other reactors made with the same technology. The system is also safer and makes the possibility of a nuclear accident comparable to the (few) in the past extremely remote.

TerraPower has made agreements with the Chinese government to build a prototype of the new reactors, but the activities have recently stopped due to the so-called "trade war" with China wanted by US president Donald Trump, which led to a suspension of the agreements . According to many observers, the solution proposed by Gates should be tried, because it is one of the most promising to change the way we produce electricity through fission.

Fusion and renewable sources
In the energy sector, people have been researching alternatives to fossil fuels for years. According to the Intergovernmental Panel on Climate Change, the scientific organization of the United Nations that deals with global warming, by 2030 the emissions of carbon dioxide on a planetary scale should be reduced by 45 percent to prevent the global average temperature from rising by more than 1.5 ° C with more serious consequences than those we will still have to face. The problem is that to date most of the electricity is produced by burning fossil fuels, and such a rapid transition to alternative sources seems to be difficult to implement.

Given the times, except for revolutionary progress, there will be hardly any fusion reactors available over the next decade to compensate for the disposal of coal and gas plants. For this reason the most viable solution is considered to be the use of renewable sources, such as wind and solar energy, whose operating costs have fallen considerably in recent years. The problem is that solar panels and wind turbines supply electricity intermittently and do not allow the peaks to be easily managed, ie the moments when greater amounts of energy are required, such as fossil fuel or fission plants.

(Tesla)

A solution could be offered by the new generation current accumulators: huge batteries that collect the electricity produced and not used during the low demand phases, then supplying it to the electricity grid when the peaks occur. Tesla, Elon Musk's company, has already implemented some solutions of this kind on a small scale, but many wonder if the model can be applied on a large scale and at sustainable costs.

Even with the best possible integrated system, with current technologies no country will be able to produce electricity solely from renewable sources, and this is one of the biggest motivations that push researchers to work on a somewhat crazy idea how to bring a piece of Sun on the Earth.



Source link
https://www.ilpost.it/2019/11/10/centrali-fusione-nucleare/

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