Nuclear power and fourth generation reactors

Looks like it’s now closed and forever forgotten. Instead, after two opposing referendums (the 1987 referendum and the 2011 referendum), nuclear power today is making a name for itself. Because if it’s true that the Green Deal we’re committed to requires us to bring our net greenhouse gas emissions balance to zero in Europe by 2050, it’s also true that we have to get energy somewhere. And nuclear power, with all its drawbacks, has an undoubted advantage: it does not produce greenhouse gases.

This issue became substantive again at the beginning of 2022, when the European Commission decided to include nuclear energy in the list of economic activities considered sustainable from an environmental point of view, the so-called “classification” that the European Green Agreement envisaged as an essential tool. To guide governments and companies in their development choices.

Is it true that we should use it? Is it correct to classify this type of energy as “green”? Beyond logos, it’s important to understand what we’re talking about. This article aims to explain how the new generation of nuclear power plants works, what are the advantages and risks involved.

chain reaction. The principle underlying all nuclear power plants is fission, according to which the nucleus of a large mass element such as uranium-235 splits into two smaller nuclei by emitting a neutron (atomic nuclei consist of neutrons and protons bound together by nuclear forces). This free neutron, in turn, can strike another uranium-235 nucleus, triggering another cleavage reaction. In this way, a sequential process that generates energy and other waste elements (slag) can be started.

The energy that is released is large, much more than can be produced by conventional chemical reactions of combustion; This is the reason for building these factories. Waste, and accidents such as those in Chernobyl (1986) and Fukushima (2011), on the other hand, are the main reasons why nuclear power is resented by large sections of the population. In the meantime, technology has made progress, so in a relatively short period of time we have moved from the first generation of experimental reactors, such as the one in Latina in 1963, to the fourth generation that has already begun to be studied and that promises to solve even the waste problem; Not only the future, but the existing as well. In between, there is an endless array of solutions on which the discussion must focus.

Better passive safety. “Today in the world there are 440 power plants, almost all of them are of the second generation, designed in the past 15-20 years, and they are generally in good working order,” explains Marco Ricoti, professor of nuclear plants at Milan Polytechnic Institute. “They produce about 10% of the electricity, but the percentage is higher in developed countries: Europe, which has more than 100 reactors, produces almost a third of its electricity from nuclear sources.”

To refer to generations, as is customary, there are actually no official classifications. “In general, the first generation of reactors is the one that was born in the 1960s and 1970s,” Ricotti explains. The reactors were small, about 2-300 megawatts (MW, or millions of watts) of power.

The second generation was developed after this somewhat pioneering phase, and features increasingly larger reactors, to cut costs on the basis of an economy of scale: nuclear power – unlike fossil fuels – actually requires high investment. factory, while operating costs are relatively low.”

Fukushima power plant after the tsunami.

second generation Fukushima power plant after the tsunami.

The second and third generation. Thus in the 1980s and 1990s construction began of 1200-1300 megawatts of reactors, such as the Montalto de Castro reactor (later suspended after the referendum) and the infamous Fukushima reactor in Japan. Remember that most of the existing reactors are of this type. And in many cases, its life is extended from 10 to 20 years with improvements in fuel, components and safety. “Since 2000, mainly third-generation reactors are being designed, for example AP1000 in the United States, VVER-1200 in Russia, French EPR. The Chinese are also developing new machines,” continues Riccuti. In the world there are 50 reactors under construction. Compared to the previous generation, the entire design of the power plant has been improved: volumes have increased (up to 1600 MW), but above all the concept of passive safety was introduced ».

The idea is as simple as it is revolutionary: Instead of having additional emergency systems that activate if something goes wrong, natural phenomena such as spontaneous circulation of coolant, which move up when it’s warmer and when it’s cooler, are used. Go down, close the cycle (Fifth. open diagram). “With these safety systems, the Fukushima accident will probably be avoided,” emphasizes Rikuti, recalling how in this case the reactor’s emergency cooling system, which is powered by diesel, was stopped due to the tsunami. The passive system will continue to operate.

Collectible, like Lego. Among the third-generation reactors, other solutions are also on the table. “In 10 to 15 years, we should also have what are called small modular reactors, that is, small reactors with a capacity of 100-300 megawatts, such as first-generation reactors,” explains Ricoti. “It may seem like a step back, but it is not: the whole design has changed. Many components that once stood outside the reactor (pumps, steam generator, etc.) have now been combined into a single structure, simplifying the design and facilitating the adoption of passive safety systems. In addition, being small, these reactors cost less and therefore have less financial risk. ” In fact, it can be considered as Lego, because it consists of standard parts that are assembled on site, avoiding huge construction sites. This allows the construction of large power plants consisting of smaller units that are added over time.

Flamanville nuclear power plant

third generation The construction site of the third generation EPR (European Pressure Reactor or Evolutionary Power Reactor) in Flamanville, France. On the left are the first two reactors, on the right, the Flamanville 3 reactor whose construction began in December 2007. It was supposed to be completed in 2012 at a cost of 3.3 billion euros. The project has faced many construction problems and is expected to be completed by the end of 2022 at a cost of €19.1 billion.
© Schoella / Panoramio / CC Commons

in miniatures. Finally, there are the microreactors, which are smaller (1 to 10 MW) and easier to build. “They are designed for specific purposes, such as mines, structures located in isolated or hard-to-reach places, and emergencies,” explains Ricotti. In fact, microreactors can be kept in a container and moved when needed.

However, the most advanced lines of research relate to the fourth generation. In this case, the main difference is in the reactor core. In fact, all current plants are based on an idea dating back to Enrico Fermi: immersing fuel rods in water to cool them and at the same time slow the speed of neutrons emitted by reactions that travel from one rod to the other. Doing so, Fermi understood, increases the likelihood of fission of the main fuel used, uranium-235. In practice, nuclear combustion occurs much better.

So reactors up to the third generation, based on this idea, are said to use “slow” neutrons. “The fourth generation, on the other hand, uses fast neutrons,” explains Ricoti, “so there are no longer rods immersed in water. These reactors must be cooled in a different way, especially liquid metals (sodium, lead or molten salts) – which exchange heat well – or gases at high temperatures.” They are more complex and expensive systems, still in development, but they look promising.

The fourth generation Fourth-generation power plants, such as the Proryv (“Turn”) project in Russia, promise the ability to solve the problem of radioactive waste as they can “burn” the most dangerous.
© Focus

Perfect recycling. The beauty of this technology is that it allows you to use more abundant nuclear fuel (uranium-235 is rare and expensive) and even has excess neutrons that can also be used to “burn” the most dangerous nuclear waste, transuranium elements, which have a very long life.

“The Russians, who are far ahead on this front and would like to have an experimental reactor by 2029, are actually building a triple plant (In the illustration above, project): one generates energy, one separates the waste (consisting of a mixture of elements) and the other introduces it into the new fuel, to be burned in the reactor. If we succeed in this, the radiotoxicity time of the spent fuel will take from 100,000 years to 300 years, and there will be no need to search for stable and deep geological sites to preserve them.”

There will also be another advantage: the uranium-235 and plutonium used in current reactors can also find applications in the development of atomic weapons. Using other fuels, fourth-generation reactors could pose fewer geopolitical problems.

Comparing nuclear and industrial waste

The graph schematically shows the amount of nuclear waste generated in the world each year, in proportion to the often overlooked toxic industrial waste. (Sources: Nuclear and Renewable Energy (Rome: Accademia Nazionale dei Lincei, 2000), updated with data from the European Commission, Radioactive Waste Management in the European Union (Brussels: European Commission, 1998).
© Focus

Returning to the growling, Ricoti still thinks that even today, while the problem is undeniable, it’s more contained than it sounds: “Just make a little comparison,” he says. “Each year Europe produces millions of tons of harmful toxic waste (arsenic, mercury, etc.) through industrial activities. Nuclear waste, also in Europe, is thousands of cubic metres. There are orders of magnitude difference (Fifth. Chart above), not that chemical waste is less dangerous. Hence, the scale of the problem is greatly exaggerated. And then, until yesterday, there was no solution to the most dangerous radioactive waste. But, as we have seen, in a few years (hopefully, soThere will be a solution.”

This article, also published in Focus 352 (February 2022), is part of a series called Focus on the next 30 in which we tell you how the world of science and technology has changed (and how it will change in the future) in light of the achievements of the past thirty years, that is, since Fox, whose first issue was published in 1992. Let us recall some of the topics we wrote about then, report on progress in the meantime and explain What awaits us in the next (30) years.

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