02 Jun 2025, 11:11
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Global

Q&A: Nuclear fusion - Hype or hope for a cooler planet?

Nuclear fusion could provide limitless, safe, climate-friendly energy - in theory. Countries such as Germany, the US, China, Japan and the UK, as well as the European Union, are investing billions of euros in developing this technology. But is it a viable strategy for achieving climate neutrality, as some proponents suggest? Or is it a harmful distraction from other methods of reducing emissions, as sceptics argue? This Q&A addresses the most significant questions surrounding nuclear fusion, based strictly on scientific consensus.

Please note: We have inserted sources into this Q&A in academic style to remind readers that these texts represent the scientific consensus as accurately as possible - See question 11 to find out more.

This text is part of our new package about frontier climate technologies, which includes further Q&As, factsheets, and interviews.

1. What is nuclear fusion?

Nuclear fusion is the process through which light atomic nuclei are fused together to produce heavier nuclei, generating energy in the process. In principle, this process is what happens in the Sun, which also produces energy, in the form of light and heat, through the fusion of atomic nuclei. To replicate this process here on Earth, the fusion of two different varieties of hydrogen atoms (deuterium and tritium) is considered to be the most promising. These light nuclei lose some mass during fusion, which is released as energy.

Nuclear fusion produces an extremely hot mixture of particles, called plasma. The aim is to use this heat to turn water into steam, which can then power conventional steam turbines and generators to produce electricity and/or heat. To set the process of nuclear fusion in motion, temperatures of around 150 million degrees Celsius and very high pressure are needed to overcome atomic repulsion, which keeps atoms apart under normal conditions.

There are various types of nuclear fusion. While so-called magnetic fusion uses powerful magnets to create the conditions necessary for fusion and hold the resulting plasma in place, inertial or laser fusion uses an array of laser beams for the same purpose. All approaches are at an early stage of research and cannot yet be used on an industrial or commercial scale.

The central challenge in nuclear fusion is generating more energy than is needed to trigger it. This has not yet been achieved. In December 2022, a team at the Lawrence Livermore National Lab (LLNL) in the USA reported a positive energy balance (in the narrow sense) for the first time, and a repetition of the experiment produced even better results in 2023. Laser fusion was pursued here, where the fusion reaction is triggered by laser-generated pressure waves in a very small fusion chamber. Temperatures of more than 120 million degrees Celsius are generated in this so-called pellet, a tiny container filled with the fuel, usually a mixture of deuterium and tritium. However, numerous media reports and public debates have ignored the fact that the energy used to generate the laser pulses must also be taken into account in the overall energy balance. If this is considered, far more energy had to be used for this fusion reaction than was generated (see section 6 for the technical hurdles for a fusion reactor).

Work in progress at the nuclear fusion reactor "Wendelstein" in Greifswald, Germany. Image by Max Planck Gesellschaft
Work in progress at the nuclear fusion "Wendelstein" research facility in Greifswald, Germany. Image by Max Planck Gesellschaft

2. How does nuclear fusion differ from nuclear fission/conventional nuclear power?

Nuclear fusion and nuclear fission are different types of nuclear energy. Both utilise the binding energy within atomic nuclei, but in very different ways. Nuclear fusion fuses light atomic nuclei, like deuterium and tritium, to form helium. In conventional nuclear fission on the other hand, heavy atomic nuclei – for example those found in uranium or plutonium - are split. There are considerable differences between the two technologies.

Availability

The first nuclear fusion reactors were already being considered in the 1950s, alongside the first nuclear power plants (NPPs); however, only nuclear fission was actually able to supply electricity at that time. The hurdles to using nuclear fusion were too high back then, as they still are today (see section 6). Compared to fusion reactors, conventional nuclear power plants are a mature technology. Investment into research and development totalling many billions of euros will be needed if fusion is to become a viable energy technology.

Waste

An important difference lies in waste streams. Nuclear fission in conventional nuclear power plants produces radioactive waste with a very long half-life (Reid et al. 2021), which requires long-term, secure storage. This poses an environmental and safety risk, and discussions about final storage for the waste are highly controversial in many cases. Nuclear fusion, on the other hand, produces helium gas, which is not radioactive. However, radioactive substances are formed in the chamber materials of a fusion reactor, the half-life of which is at least one hundred years, depending on the material. These must also be safely disposed of, but this is much easier than dealing with spent fuel rods from a conventional nuclear power plant (Zinkle/Snead 2014).

Security

One of the biggest challenges in nuclear fusion is achieving the specific conditions required for fusion to occur in the first place. If an accident were to occur in a nuclear fusion reactor, these conditions would no longer exist and the entire process would stop. In the reactor of a conventional nuclear power plant, on the other hand, accidents can lead to meltdowns and result in large-scale and long-lasting environmental pollution, as in Chernobyl in 1986 or Fukushima in 2011. This is because nuclear fission sets a process in motion that is self-sustaining and must be meticulously controlled. In the event of a problem, a chain reaction can get out of control and cause devastating damage. The process in a nuclear fission power plant is very similar to that of a nuclear bomb, but in a slowed and controlled manner.

Arms control

Nuclear power plants can be used indirectly to build nuclear weapons because they produce plutonium as a byproduct, which is suitable for weapons after reprocessing and enrichment, which increases the concentration of certain types atoms needed for fission. Fusion reactors, on the other hand, produce neither uranium nor plutonium during normal operation. And the radioactive tritium used for fusion cannot be used to build a nuclear bomb without fissile material. There are other theoretically conceivable ways of using a fusion reactor to build nuclear weapons, but these can be relatively easily monitored. A study on the subject came to the clear conclusion that "the proliferation risk from fusion systems can be much lower than the equivalent risk from fission systems, if the fusion system is designed to accommodate appropriate safeguards" (Glaser/Goldston 2012).

Raw materials

Last but not least, conventional nuclear power plants and fusion reactors differ considerably in terms of the raw materials they require to operate. Deuterium and tritium would likely be needed for fusion reactors, and in comparatively small quantities. While deuterium occurs naturally in sufficient quantities, tritium must be produced through a reaction of lithium with neutrons. This can be done perspectively done with neutrons that are produced when fusion occurs. However, very large amounts of lithium are also needed for renewable energy technology and electric vehicle batteries, the limited supply of which has been described as a problem for the feasibility of fusion (Junne et al. 2020). In principle, however, the fuel issue in nuclear fusion is considered to be relatively easy to solve. Nuclear power plants, on the other hand, require (enriched) uranium or plutonium, which is rare, expensive, partly very toxic and complex to produce, compared to the available materials for nuclear fusion.

3. What are the advantages of nuclear fusion?

Nuclear fusion itself is a carbon-neutral source of energy (even if greenhouse gases are currently emitted during the construction of the reactors and the generation of the energy used to power the reaction). In addition, nuclear fusion is a very efficient energy source from a purely material point of view. According to the Max Planck Institute for Plasma Physics, one gram of fusion fuel could theoretically provide as much energy as eleven tonnes of coal.

Compared to wind and solar power plants, fusion reactors would have the advantage of being able to generate a great deal of energy regardless of the weather (this is referred to as secured or guaranteed power, more on this in section 7). They also require much less space. Although there are no exact figures for fusion reactors as they do not yet exist, nuclear power plants, for example, require on average only around 0.4 to 4 percent of the area of solar or wind power plants with the same output, depending on the source (Smil 2015, Lovering et al. 2022).

4. What are the downsides of nuclear fusion?

So far, there are no useable or commercially viable fusion reactors in operation or development. For this reason, fusion cannot currently help to decarbonise the energy supply – a task that must happen at least in developed industrialised countries in the very near future and by the middle of the century at the latest, according to the IPCC (IPCC 2023, AR6, SYR, SPM.B.6). Renewable energy sources such as wind or solar power are available immediately and technically mature enough to replace CO2-intensive coal or gas power plants. In contrast, nuclear fusion is entering development too late to help meet climate targets (see also section 5).

The IPCC shares this assessment: nuclear fusion does not appear in Chapter 6 of Volume 3 of its Sixth Assessment Report (AR6) from 2022, which analyses options and technologies for reducing emissions in the energy sector. Nuclear fusion is also generally not considered in scientific energy system studies, mainly because reasonably reliable estimates of the costs and efficiency are required as input data for energy system modelling. Fusion research is at such an early stage that such estimates are not yet available.

Even if fusion power plants were already operational, they would have clear disadvantages compared to renewable energy. Only rich countries or large companies can operate fusion reactors, given that they are complex and expensive. The ITER fusion research reactor in France already shows that there is a rift running through the global community. Countries pursuing nuclear fusion technology (EU, USA, Russia, China, India, South Korea, Japan, UK, Switzerland) are at an advantage over the rest of the world (Carayannis et al. 2022). Renewable energy, on the other hand, is "low-tech" compared to fusion reactors. Solar PV systems for example, can be installed very easily and contribute not only to climate protection, but also to initial electrification and poverty reduction, even in low-income countries without a developed electricity grid (Bogdanov et al. 2021, Ortega-Arriaga et al. 2021, Wassie/Adaramola 2021).

In addition, nuclear fusion will certainly be more expensive than renewable energy in the longer term. According to one calculation, so-called tokamak-type reactors, the most common type of magnetic confinement reactor, aren’t likely to become commercially competitive until 2040 at the earliest – even under the assumption that costs fall once the technology is in use. The authors put the cost of the resulting electricity at 150 US dollars per megawatt hour (Lindley et al. 2023). A study for the European fusion programme in 2005 arrived at lower figures: 50 to 90 euros, depending on the model. Adjusted for inflation, this corresponds to around 70 to 125 euros (74 to 133 US dollars) in 2023 prices.

Even then, nuclear fusion would still be significantly more expensive than renewables. In 2024, the Fraunhofer Institute for Solar Energy Systems (ISE) found that the levelized cost of electricity in Germany for onshore wind turbines fluctuated between 43 and 92 euros and for large solar plants, between 41 and 69 euros per megawatt hour. However, in order to compare the price level with that of fusion power plants, which would supply electricity regardless of weather conditions, the costs of storing renewably-produced energy would also need to be factored in. Fraunhofer’s calculations suggest that large solar arrays with battery systems would cost between 37 and 76 euros per megawatt hour in 2045. Even if such estimates are ultimately overly optimistic, the low costs that renewable energy has already reached and will reach in the future set a very high bar for fusion reactors to compete witth.

5. When can we expect to see the first commercially viable fusion reactor?

Two types of fusion technology are currently in development (see also section 1). One is plasma-based fusion reactors, where the kinetic energy of hydrogen nuclei in a very hot plasma is used to initiate the fusion reaction. Two designs exist here, known as tokamaks and stellarators, and there is currently intense debate among researchers as to which variant should be pursued further. Both governments and private companies are currently developing both types of fusion reactors. The forecast date of both groups for a first operational reactor differs significantly.

The ITER facility in France, which is currently being built by Europe, China, India, Japan, South Korea, Russia and the US, in 2024 postponed the target date for energy producing fusion reactions – the goal of the project - to 2039. The first demonstration reactor, which could be connected to the European power grid for testing purposes, is scheduled for operational trials around 20 years later, by in the mid-2050s, according to the European research plan. A fusion reactor that is part of an energy supplier's power plant fleet is expected much later.

But fusion start-ups argue that the ITER timetable is not a good indicator for the technology’s progress. They say the political nature of the project, the complicated coordination between many states, the integration of components delivered from across the globe, bureaucracy, as well as its massive size, make ITER inherently slow. Private companies are not held back by these constraints, allowing them to move much faster.

This is why the timetables of private companies are much more ambitious. US company Helios wants to produce electricity as early as 2028; Commonwealth Fusion, also based in the US, aims for the world’s first grid-scale commercial reactor in the early 2030s; German start-up Proxima Fusion plans to launch a reactor capable of continuous operation in 2031, “opening the door to the commercial application of fusion energy”.

However, ever since the first fusion reactors were planned, schedules have had to be reconsidered. In 2004, for example, the ITER researchers believed that the first demonstration reactor could go online in 2033. Eight years later, they pushed this back to the early 2040s, and in 2018, the reactor was finally announced for the 2050s. A study reviewing the progress of fusion research stated that:

"It is therefore important to state that roadmaps from enterprises, both public and private, are not considered to be credible sources for timescales of fusion. Many developers have published pathways to commercialisation that are a moonshot approach, in other words all milestones are achieved with no showstoppers, delays, and assume that there is adequate funding for all the activities at each step. […] That is not to say that that the timescales are un-achievable, but these are often optimistic in order to attract investment and are lacking in accompanying data that back up predictions.” (Griffiths et al. 2022)

Opening schedules weren’t the only things to be underestimated in the past, but also cost forecasts. In the case of the international ITER project in Cadarache in the south of France, the estimates were around EUR 5.9 billion (excluding the contributions in kind that the project partners in the participating countries are providing on their own responsibility) in 2008. Two years later, the EU Commission already assumed that it alone would have to contribute 7.3 billion euros (as the European Union bears 45.5 per cent of the total costs, this corresponds to a tripling). In 2016, ITER increased cost estimated to 22 billion euros. In May 2022, the European Parliament in a resolution expressed its concern that there was a risk of further "significant cost increases and/or further delays in the implementation of the ITER project". When project management presented a new, postponed schedule in July 2024, there was also talk of further cost increases of five billion euros.

The second type of fusion that is distinct from plasma-based fusion is laser or inertial confinement fusion. The successes of the Lawrence Livermore National Lab in the USA (see section 1) has given this approach strong tailwind. The race for the best, cheapest, most efficient, and most rapidly available concept is thus wide open. A number of start-ups with strong financial backing are aiming for rapid commercial realisation of laser fusion technology. However, estimates of future costs and timetables remain unreliable.

6. What are the technical hurdles to a functioning fusion reactor?

Fusion research has achieved considerable success since the 1980s, but there are still many problems to be solved. The specialist literature lists a number of hurdles that need to be overcome before functioning fusion power plants can be realised (see, for example, Donné et al. 2017; Takeda/Pearson 2018):

  • Firstly, plasma-based fusion reactors have not yet succeeded in reliably generating and handling the energy-rich plasma and keeping it stable long enough for it to be utilised.
  • Secondly, there is still a lack of special materials for them that can contain the plasma and withstand both high heat and radiation.
  • Thirdly, it has not yet been fully clarified how the heat generated can be captured and dissipated so that it can be used outside the reactor to produce electricity or heat.
  • Fourthly, it has not yet been possible to establish a genuine “tritium cycle”, which involves producing tritium using the fusion reaction itself, extracting it, processing it, and returning it to the fusion plasma for fuel. This is theoretically possible and in practice essential for nuclear fusion, because the only source of tritium to date has been certain older types of nuclear power plant, which are gradually being shut down. From the mid-2030s, fusion research could therefore face a supply problem.

The other type of fusion, laser or inertial fusion, also still has a number of problems to solve. For example, a continuous fusion reaction would require many improvements regarding the burning time in the reactor and a continuous supply of new fuel pellets.

Some critics of fusion research have described at least some of the problems mentioned as unsolvable.

7. Are fusion reactors and renewables compatible?

If the first commercially viable fusion power plants are connected to the grid from the 2040s in an optimistic scenario, or from the 2060s in a conservative one, the electricity grid in the major countries is likely to be dominated by a mixture of renewable energies and nuclear power plants. This is because the EU as well as China and the USA have announced their intention to be climate-neutral between 2045 and 2060. Several studies dealing with the future role of fusion power plants assume this scenario (Hamacher et al. 2013; Nicholas et al. 2021). Several other studies show that the respective demand for energy projected in different countries could theoretically also be covered by renewable energy alone (Breyer et al. 2022; Zappa 2019). In any case, there is a consensus among researchers that renewables will cover a very large proportion of global energy demand in a few decades. Fusion proponents argue that rising electricity demand, for example for data centres running AI, will require additional sources to complement renewables.

The question is what role fusion power plants can and should play in a future electricity system. Like gas, coal or nuclear power plants, fusion power plants are what is referred to as "base-load capable" in traditional energy systems. This means that they can meet a certain amount of energy demand at all times, regardless of weather conditions. However, the higher the proportion of renewable energy in an energy system, the less important (or even obstructive) "base load power plants" with continuous production become, as flexibility and rapid controllability become more important. The key question might be whether a power plant can step in rapidly when solar and wind are not supplying enough energy.

In principle, fusion power plants are able to adjust their output (Ward/Kemp 2015). However, ramping up and down worsens the economic efficiency of the plants. According to various studies, in the energy supply systems of a decarbonised world, fusion power plants will compete with two other technologies to serve as a supplement to the cheaper but fluctuating renewables: fission nuclear power plants on the one hand, and gas-fired power plants with CCS capture facilities on the other. However, as fusion reactors will produce comparatively expensive energy even at full load (see section 4), they may need to be subsidised or otherwise (politically) supported in order to survive on the market.

A study that specifically analysed the possible role of fusion power plants in a future energy system dominated by renewables came to the following conclusion:

"While there remains a clear motivation to develop fusion power plants, this motivation is likely weakened by the time they become available." (Nicholas et al. 2021)

A reactor that can supply so-called base load energy could be obsolete in the post-fossil energy future, the research team warns. It therefore urgently recommends that fusion research and the design of future reactors pay more attention to their flexible controllability. German research academies also said in late 2024 that an energy system dominated by solar and wind energy does not require baseload power stations to guarantee supply security.

Some studies also see a possible role for fusion reactors in the production of hydrogen, which is to play a key role in a climate-neutral energy system and will then be needed in very large quantities (Gi et al. 2020). Fusion proponents also argue that the technology could not only serve to generate electricity, but could also be used to supply heat to industrial processes.

8. Are there any other hurdles?

In addition to technical and financial hurdles, public opinion could also become a problem for nuclear fusion. Examples of other technologies, such as nuclear power in Germany, show that social considerations can ultimately determine whether and how a technology is utilised.

There are therefore already discussions among fusion advocates about how to ensure a positive social framing for this new technology (Hoedl 2023). For example, a study with test subjects from the UK and Germany found that fusion reactors could face acceptance problems if they were lumped together with conventional nuclear power (Jones et al. 2019).

The German parliament’s Office of Technology Assessment also emphasised that "Social acceptance of fusion technology will depend to a large extent on environmental criteria being adequately taken into account at the time of technology decisions. [...] In order to avoid crises of acceptance and trust, an early, intensive and open-ended dialogue between science, interest groups and the public is required." (Grunwald et al. 2002)

9. What is the EU’s role in nuclear fusion?

The development of fusion science and technology in Europe gained momentum with the 1957 Euratom treaty, which established a European atomic energy community. Since then, Euratom has coordinated European fusion research by funding initiatives such as the Joint Undertaking Fusion for Energy and EUROfusion, which aim to accelerate the development of fusion plants. The ITER agreement, signed by Euratom along with China, India, Japan, South Korea, Russia and the US, is responsible for managing and constructing the ITER facility in France. The goal of the project is to prove that a plasma-based fusion reactor can produce ten times the thermal power injected into the plasma.

Fusion for Energy is tasked with delivering Euratom’s contributions to the ITER project. Another key initiative is the International Fusion Materials Irradiation Facility (IFMIF), a joint European-Japanese project that will be constructed in Japan and set to operate in parallel with ITER. IFMIF will test and select materials capable of withstanding the extreme conditions inside a reactor, which include very high temperatures and high-energy neutrons. EUROfusion, on the other hand, represents a pan-European consortium with 30 members across 29 countries collaborating on fusion research.

The European fusion research follows a long-term strategy set out 2018 in the European research roadmap which charts the path for achieving fusion energy connected to the grid in the second half of the century. ITER is pivotal to this roadmap, because it is meant to prove the scientific and technological feasibility of this approach.

Despite fusion research dating back to the 1950s, to date only the US and the UK have established regulatory frameworks. The EU Commission has lamented that the absence of national and international rules creates a “regulatory vacuum,” which could potentially lead to the application of very strict (and hence expensive and obstructive) fission power-plant regulations to fusion power plants, which would complicate development. This has been the case for the ITER facility, which was classified as a nuclear reactor facility and thus subjected to a fission-based regulatory framework. However, there are compelling reasons why a fission regulatory approach would not be appropriate for fusion (as pointed out in section 2).

Ursula von der Leyen, president of the European Commission, affirmed need for action. “We need to put in place a specific regulatory framework for nuclear fusion,” she said, adding “we need to send a clear political signal that this is also a secure investment for private capital.” Later, the EU adopted the Net Zero Industry Act, which included a list of net-zero technologies and also covered nuclear fusion under “other nuclear technologies.” The act sets the target of producing 40 percent of net-zero technologies deployed in Europe on the continent by 2030, and to capture 25 percent of the global market value for these technologies. It also intends to deal with the challenges in scaling up manufacturing capacities in these technologies.

The Fusion Industry Association, representing the private fusion sector, advocates for fusion to be listed as a distinct subcategory of net-zero technologies. According to the association, this distinction is crucial, because conflating fusion and fission could result in unintended complications in both regional and international markets.

10. What is Germany’s approach to fusion energy?

In Germany, there is no law specifically regulating fusion facilities. The German Atomic Energy Act, a law on the peaceful use of nuclear energy and protection against its dangers, does not apply, as it is limited to facilities using fissile materials like uranium or plutonium. Germany’s largest fusion facility, the Stellarator Wendelstein 7-X run by the Max Planck Society, is regulated under the German Radiation Protection Act, which provides the legal framework for comprehensive protection against harmful radiation. The German government’s committee on “Education, Research and Technology Assessment” held a consultation in July 2024 on the legal framework for fusion power plants in Germany and Europe, where various stakeholders spoke out in favour of a clear delineation of fusion from fission.  

With the introduction of the Fusion 2040 funding programme, which encompasses both laser and magnetic fusion, Germany is investing over one billion euros in fusion research until 2029. When unveiling the programme in 2024, then research minister Bettina Stark-Watzinger said Germany should use its “pole-position” in the technology to pioneer the construction of a fusion power plant, by creating an “ecosystem” of industry, start-ups, and science. This aspiration was echoed by Germany’s new government, which promised more support for nuclear fusion research in its 2025 coalition treaty with the goal of building the world's first fusion reactor in the country.

11. Why does this text reflect the "scientific consensus"?

Scientists have accumulated a surprising amount of specific knowledge about how effective various technologies can be. Their findings can be found, for example, in the IPCC’s Sixth Assessment Report, which runs to more than 2000 pages.

To highlight that the selection of sources is central to this project, we have deviated from our usual editorial guidelines in this Q&A, and inserted sources in academic style - to remind readers that these texts represent the scientific consensus as accurately as possible.

With this aim in mind, we ranked sources in the following order, which values relevance much more than a very recent publication date:

1)     Wherever possible, the texts rely on the IPCC, which provides highly reliable summaries and assessments of the state of research.

2)     A second-best are thorough meta-studies (studies that evaluate many other studies), as well as synthesis reports from large research consortia or organisations, where a broad circle of participants and intensive review processes are common.

3)     Only in third place, we used individual studies - limited to publications in recognised research journals that guarantee a peer review process, meaning each publication is checked by competent specialist colleagues.

This Q&A and others in this series are based on texts published by our German-language sister project Klimafakten, which were written by expert journalists, and double checked by relevant experts. Two foundations supported this editorial project, which was overseen by our colleague Toralf Staud: the Marga und Kurt Möllgaard-Stiftung and the Deutsche Bundesstiftung Umwelt.

All texts created by the Clean Energy Wire are available under a “Creative Commons Attribution 4.0 International Licence (CC BY 4.0)” . They can be copied, shared and made publicly accessible by users so long as they give appropriate credit, provide a link to the license, and indicate if changes were made.

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