Nuclear energy is a hot topic whenever it is discussed. On the one hand, this type of energy generation is considered one of the alternatives with the greatest potential to meet the world's energy needs today. On the other hand, its turbulent beginnings and a long history of accidents since its adoption raise more than one eyebrow when the subject is brought up in any conversation. Therefore, when the question “would you want to live next to a nuclear power plant?” is raised in conversation, the first thoughts that usually cross the other person's mind are the Chernobyl accident, the more recent Fukushima accident, or the issue of nuclear waste. These thoughts, therefore, are usually answered with a resounding “no”.
Fortunately, science continues to advance, and the latest models of nuclear reactors are true safety fortresses. In addition, thanks to the application of new technologies, these plants have become so efficient that they can even use radioactive waste from other plants to minimise their impact on the environment. But it is not all about improvements to classic power plants. New nuclear power plants are also being developed that use thorium as fuel or molten salts instead of water to transfer the heat from the plant's core.
Thus, despite its many bright spots, the long shadow of nuclear energy is casting a shadow over a debate that is anything but straightforward. Like all science, new forms of energy generation from nuclear sources have their advantages and disadvantages. But the former seem to place nuclear energy as one of the linchpins of the society of the future and key players in the ecological transition to a more sustainable future. With 80 years of research behind it and a well-established foundation, the future of nuclear energy can only go forward. To this end, it continues to reinvent itself and to offer new possibilities that match today's reality.
INSIDE. A difficult but possible nuclear alternative
The growing consequences of climate change have led humanity to realise that it needs to rethink the current way of life in order to avoid the collapse of the biosphere. A transition must be made to a more sustainable world, one that makes better use of its resources and has a clear objective: to leave the smallest possible footprint on the environment. However, to achieve this ecological transition and to continue to maintain the comforts of the contemporary world, one of the keys is to guarantee the supply of energy in a way that is clean and consistent with needs.
Following this trend, renewable energy sources, such as solar, wind, hydro, tidal, as well as other minority options, are presented as the most suitable alternatives to achieve complete decarbonisation in the electricity sector. Spain has been a benchmark country in the adoption of renewable energies. Currently, according to Red Eléctrica data, 56.8% of all electricity produced in Spain in 2024 came from renewable sources, the highest figure in a series that has been trending upwards for years. Of the renewable energy mix, wind generated 23.2 % of the total, solar 17 %, hydro 13.3 % and the rest, the remaining percentage. [1]
On the other hand, the seven nuclear reactors located in Spain's five power plants produced another 20% of the total energy, which places only around 23% of the energy generated in our country as coming from sources that release greenhouse gases into the atmosphere. The seven nuclear reactors are capable of producing this amount of electricity by harnessing the heat energy emitted by the uranium atoms as they disintegrate. Specifically, the Spanish reactors in operation, built between 1983 and 1988, are of the PWR class (PWRs).Pressure Water Reactor or pressurised water reactor)[2]. The main feature of this type of reactor is that it has two water circuits to transfer the heat generated in the core of the plant and thus generate electricity.
The first circuit, which is in contact with the core, is closed. In it, water is heated and, as it heats up, it tends to turn into vapour. This is the reason why it is kept at a high pressure: it prevents the liquid from becoming gaseous beyond its boiling point. The hyperheated water pipes come into contact with a second circuit of water that can be converted into steam and drives the electricity-generating turbines. Once it has done its job, the remaining steam escapes through the cooling towers, and the remaining hot water is cooled in reservoirs until it reaches a temperature suitable for return to the environment.
Thanks to this design, an operating nuclear power plant emits only water into the atmosphere and, due to its stability in electricity production, can act as a safeguard for shortfalls in renewable energy production.
However, every technology comes at a cost. Uranium is an extremely scarce element, barely representing 0.0004 % of the weight of the earth's crust. Therefore, according to data from the Spanish nuclear society, only 55,000 to 60,000 tonnes of uranium metal are extracted each year. Of this uranium, 99.27% is uranium-238, and only 0.72% is uranium-235, which is needed in greater proportion to be used as fuel. Therefore, before being used in Spanish nuclear power plants, uranium requires prior enrichment, i.e. an increase in its concentration of uranium-235 to 3% or 5%. For this purpose, different solvents are used to create uranium hexafluoride and gaseous diffusion or ultracentrifugation techniques are used to reach the appropriate percentages. At the end of the process, the result is enriched uranium oxide.
Neither the extraction of the fuel nor its subsequent enrichment is carried out in Spain. The uranium mines with the highest production are in Kazakhstan, where some 20,000 tonnes are extracted each year, followed by Australia with 6,500 tonnes and Namibia with 5,500 tonnes.[3] There have been negotiations to extract and enrich uranium in the Salamanca village of Retortillo, where it is estimated that there are around 25,000 tonnes of uranium.[4], The mine would be enough to supply the needs of Spanish power plants for 20 years. However, the exploitation of this mine could have a profound impact on the orography and ecosystems of the region. This fact, together with the plans to close and dismantle the current power plants by 2035, led the Ministry of Ecological Transition to scrap its operation in 2022.
The storage of waste from nuclear power plants is also a serious problem. At present, the only radioactive waste repository in Spain is located at El Cabril, in the province of Cordoba, which is managed by the public company ENRESA. This repository for intermediate, low and very low level waste occupies the galleries of uranium mines closed in 1956. All materials from hospitals, companies and industry that emit some radiation, such as the clothing of nuclear power plant workers, or medical instruments used in nuclear medicine, end up there.[5]
Instead, high-level nuclear waste is stored in the nuclear power plants themselves for several decades until it is safe to send it to a deep geological disposal facility. Currently, the most important in the world is the Onkalo project in Finland, a mega-construction where spent nuclear fuel from dozens of power plants will be buried. However, this construction is not without its critics, as there are risks associated with the management of this waste, which will have to be maintained for thousands of years.[6].
For these reasons, new technologies related to nuclear power plants have been designed with these problems in mind and with the idea of addressing any complications before they occur. Some new generation models are so efficient that they can even use waste from other nuclear power plants as fuel, which helps to reduce the volume of radioactive waste and to give a new use to existing waste, i.e. to transform it into a new resource. Figure 1 shows one possible alternative.
One of the most promising technologies in this respect is the molten salt reactor or MSR, whose operation can be seen in Figure 2. This type of reactor uses different salts (chlorine, fluorine, lithium or mixed salts) that are melted to transfer heat from the reactor core to the external loops or to the external water circuits. Molten salts are currently used in industries and other power generation systems because of their high calorific value and stability. For example, the solar thermal power plants at Los Arenales and Gemasolar (Seville) use molten salts to collect the heat reflected from the mirrors and deliver it to the power generation systems.[7]. In other words, it is a technology that is used effectively in other contexts and is known to work and has great potential for nuclear power generation.
During the 1960s and 1970s, at the height of the atomic age, the viability of this type of reactor was studied in different experiments carried out in the United States, the United Kingdom and the former Soviet Union. However, due to competition with other types of reactors, and the lack of knowledge of the other key players in the investment decision-making process, the various research programmes for this type of reactor gradually disappeared.[8].
But in the early 2000s, due to the new climate paradigms discussed at the beginning of this chapter, research centres became interested again in molten salt nuclear reactors. This type of reactor has a number of advantages[9] compared to LWRs, but also disadvantages.
Advantages:
- Molten salt reactors can operate at high temperatures, providing high thermal efficiency. This reduces size, cost and environmental impact.
- A low-pressure MSR could have lower costs for both core containment elements and piping and safety equipment.
- In some designs, the fuel and coolant are a single fluid, so that a loss of coolant drags the fuel with it, avoiding the risk of explosion.
- The waste produced by these plants is mostly fission products with short half-lives. This can reduce the necessary containment of the waste to a few hundred years, compared to tens of thousands of years for spent fuel from LWRs.
- Fuel rods are not to be manufactured, but the salts are to be synthesised.
- Such reactors could exploit radioactive waste or thorium as fuel, an element that emits much less radiation.
Disadvantages:
- In circulating molten salt designs, radioactive elements come into contact with equipment such as pumps and heat exchangers. Therefore, maintenance of the equipment should be fully remote.
- Molten salts require careful management of their oxidation state to control corrosion risks. This is a technical challenge, as it requires interchangeable modular parts to achieve greater efficiency.[10].
- Some MSR designs can be converted into nuclear material factories compatible with modern nuclear weapons.
- Regulatory changes are needed to accommodate the characteristics of these reactors.
- There are still no independent studies to validate its economic viability.
Over the last few decades, thorium has gone from being an element that was used in fewer and fewer applications for fear of its radioactivity, to one of the central axes that can shape the electricity generation of the future. Graph 3 provides relevant information to learn a little more about this actinide element, with atomic number 90, which is found almost entirely in its 232Th isotope, an element with a half-life of 1.405×10¹⁰ years. In its pure state it is a soft, silvery-white metal, which in contact with air gradually blackens by oxidation, and is named after the Norwegian mythological thunder god Thor.[11].
Trace amounts of thorium can be found in most rocks and soils at about 10.5 parts per million, three times the amount of uranium. In total, there are an estimated 12 million tonnes of thorium available for exploitation, with the largest deposits on the south and east coasts of India. There are also thorium deposits in other countries such as Australia, Brazil, Canada and the United States.
Due to its decay, thorium is considered a «fertile» material for fission. That is, although it can act as a nuclear fuel on its own, it can be used to create nuclear fuel. A thorium reactor requires uranium or plutonium to initiate and sustain the nuclear reaction. When irradiated, the thorium eventually forms uranium-233, which then disintegrates to release the energy needed to power the reactor of type Thermal Breeder Reactor.
This introduces certain advantages over uranium, since thorium is more abundant in the earth's crust, can be exploited almost entirely and, due to its operation, generates less radioactive waste. Thorium reactors are also much less accident prone.
As India has the largest reserves of thorium (almost two thirds of the world's reserves), they have been developing a type of reactor for more than a decade, called a advanced heavy water reactor thorium-fuelled. [12]China, for its part, has embraced the use of thorium and in 2023 took its first steps to try to operate an experimental nuclear reactor combining molten salts and thorium. Construction has taken place in the Gobi desert, and the feasibility of the project will be investigated over the next few years.
In the meantime, the rest of the countries are waiting for the results to see if this is indeed a technology worth exploring or whether to put it back in the drawer, as was done in the 1980s. [13]
Globally, countries such as the United States, France and China have led the way in the development and deployment of nuclear technologies. France, for example, has relied on nuclear power for most of its electricity supply for decades, while China is investing in new-generation reactors to diversify its energy mix.
The current climate shows that nuclear energy still has a long life ahead of it. Despite the burden of not being a renewable energy because of its reliance on the earth's resources, its unique conditions and decarbonising potential have made it a key player in the world we envision in the future. The technology of nuclear beyond uranium means that this controversial technology can become a great boon to the world. A world where net emissions end up being zero or even negative, a world where humanity is greener and, ultimately, a world where humans embrace their role as protectors of the environment.
IN ACTION. The road to uranium-free nuclear power is underway
The international energy community was startled in the spring of 2025 when Chinese scientists announced that they had successfully added new fuel to a molten salt thorium reactor, a technological milestone. The experimental reactor, which they have been working on for almost two decades, is located in the Gobi desert in western China, uses molten salts and thorium, but is still small, only able to generate two megawatts of thermal power sustainably.[14].
China claims to have a much larger thorium molten salt reactor ready by 2030, capable of producing 10 megawatts of electricity (slightly more than the six megawatts of the reactor used by MIT for its experiments). In addition, China's state-owned shipbuilding industry is working on a model of thorium-powered container ship, the KUN-24AP.[15], He also envisages that future lunar bases could be powered by reactors of this material.
China is not alone in seeking to exploit thorium's unique properties. Previously, India, Japan, the UK, the US and other countries have shown enthusiasm for its possible application in nuclear energy. Thorium has several advantages over conventional nuclear fuel, uranium-235. It can generate more fissile material (uranium-233) than it consumes, if fed to a water-cooled or molten salt reactor, and it is estimated that the earth's upper crust contains an average of 10.5 parts per million (ppm) of thorium, compared with about 3 ppm of uranium.[16], This poses geopolitical benefits, but also challenges for its economic exploitation.[17]. In addition, all the thorium mined can be used as fuel, compared to less than 1% for uranium.
According to official data, India, Brazil, Australia and the United States hold most of the world's thorium reserves, estimated at 6.4 million tonnes.[18]. World resources of monazite, the mineral from which it is mainly extracted, are around 16 million tonnes, 12 million tonnes of which are found in heavy mineral sands deposits on the south and east coasts of India. Another large lode deposit of thorium and rare earth metals is located in Idaho in the United States.[19], whose Department of Atomic Energy (DAE) has planned to use the large thorium deposits available in the country as a long-term option.[20].
Securing America's Future Energy (SAFE) has urged funding for thorium research to develop industrial, defence and energy applications, including a thorium bank to manage the by-product of the refining process.[21]. One third of the $750 million it considers necessary to devote to rare earth research should be devoted to thorium, while suggesting granting a federal charter to an entity to assume ownership and responsibility. In recent years, the US Congress, the Department of Energy (DOE) and the private sector have expressed considerable interest in the development and deployment of advanced nuclear reactors.[22]. The nation's National Academies formed an expert committee focused on advancing advanced reactors that could be commercially deployed by 2050, and DOE created the Clean Energy Demonstrations Office to manage the two major projects.
The main thorium deposits in Europe are in Greenland, Finland, Norway and Turkey, although no mining has taken place since 2019. It is estimated that only around 10% is economically available, including by-product recovery, but under current market conditions, thorium production in Europe is not expected.[23].
China argues that it has every reason to claim absolute leadership, even though official statistics place it in a lowly position with 100,000 tonnes. It claims to have a thorium-rich mine in Inner Mongolia that could, in theory, meet all its energy needs for tens of thousands of years, while producing minimal radioactive waste. In addition, the Bayan Obo mining complex could produce one million tonnes of thorium, enough to supply China for 60,000 years, and has identified 233 thorium-rich areas clustered in five key belts from Inner Xinjiang to the Guangdong coast, including the Fujian and Hainan coastal sands containing monazite with easily extractable thorium.[24].
Thorium is a by-product mainly of monazite, and its extraction requires more expensive methods than those for uranium, at least as long as the demand for thorium and its application in nuclear energy do not help to find ways to make them cheaper. Its separation requires large amounts of acid and energy and could generate hundreds of tonnes of wastewater for every gram of thorium purified. R&D and experiments to test thorium-fuelled nuclear facilities are also uneconomical, due to the lack of development of the industry and the historical pre-eminence of uranium. This is compounded by its difficult handling and the fact that, as a fertile, non-fissile material, it needs a trigger, such as uranium or plutonium, to activate and sustain a chain reaction. Thorium and uranium-233 are more dangerous because of their radioactivity when chemically processed and are therefore more difficult to handle.[25]. Graph 4 shows the transformative capacity of its energy.
Thorium-uranium fuel is expensive, to the extent that equilibrium with uranium would only be reached if the price of uranium doubled. However, the revenues generated by electricity sales, combined with the cost of refuelling during reactor downtime, show that it can be advantageous: a saving of 14.8% when compared over equivalent periods of time.[26]. The high cost of fabrication is partly due to the high level of radioactivity that accumulates in the U-233 chemically separated from the irradiated thorium fuel. Its recycling poses similar problems due to the presence of highly radioactive thorium (Th-228).
Some of these problems are solved by molten salt reactors, where the equilibrium fuel cycle is expected to have relatively low radiotoxicity. In that case, the thorium fuel cycle would offer energy security benefits that would allow credible long-term nuclear energy scenarios to be drawn: mastering nuclear fission thorium breeder cycle reactors could increase the amount of fissile material by more than 100 times.[27] and the thorium-uranium fuel cycle could be implemented in small modular molten salt reactors.[28], emissions, where in the long term the energy contribution of thorium could reach 89.1%.
The reality is that it is not easy to justify economically, in the short term, a commitment to commercialising thorium fuels and this slows its expansion as a possible alternative. It requires a great deal of testing, analysis and licensing to bring it into service, and this distances it from the market and complicates government support. Moreover, uranium is abundant and cheap, and represents only a small part of the cost of nuclear electricity generation, so there is no real incentive to invest in a new type of fuel today.
From a geo-strategic point of view, however, there is reason to believe that demand will underpin this exciting technology race in the future. Amazon, Meta, Google and DOW are among the signatories of the so-called “Major Energy User Commitment” that supports the goal of at least tripling global nuclear capacity by 2050.[29]. The current 391 GWe of operational nuclear capacity could rise to 686 GWe in 2040; and if global reactor uranium requirements were around 65,650 tU in 2023, they could rise to almost 130,000 tU in 2040.[30].
The Red Book, a joint publication by the International Atomic Energy Agency (IAEA) and the OECD's Nuclear Energy Agency (NEA), agrees that global nuclear energy production could increase by more than 50% by 2040, and goes beyond that date: its projection is that annual global uranium demand could be between 200,000 and 250,000 tU in the second half of the 21st century.[31]. The current mining capacity of the mines is far short of these figures, and not much can be expected from the secondary uranium supply, whose share of the world market will decrease from the current level of 11-14% of reactor uranium requirements to 4-11% in 2050.
At current global nuclear capacity, excluding the 50% build-up planned to 2040, proven uranium reserves are estimated to last about 90 years. The oceans contain this radioactive mineral at a concentration of 3.3 micrograms per litre, so could provide tens of thousands of years of supply, so scientists at Oak Ridge National Laboratory in the US have developed a material capable of adsorbing six grams of uranium for every kilogram of adsorbent material. Stormwater runoff from land masses will renewably replenish the uranium extracted from the sea.[32]. But these future options will have to coexist with new episodes of geopolitical instability, such as the recent war between Russia and Ukraine, which increase the strategic value of nuclear energy for security and energy sovereignty reasons.
It is logical that utilities, suppliers and governments around the world are therefore looking for opportunities to diversify their energy supplies. Countries with the largest reactor parks are extending the life of existing plants to 60 years, and even to 80 years in the case of the US, but more than 140 reactors will reach that limit by 2040.[33]. Small modular reactors and micro-reactors could contribute up to 10% of the total capacity in the most favourable scenario, but are not a clear alternative.
Thorium fuels require a fissile material such as inductor and the only options in that regard are uranium (U-233 and U-235) and plutonium (Pu-239), neither of which is easy to supply. It is also difficult to design thorium fuels that produce more U-233 in thermal reactors than the fissile material they consume, a process known as breeding. A different option is to use thorium as a fertile matrix for plutonium-containing fuels, such as thorium-plutonium mixed oxide fuel (Th-Pu MOX). The problem here is that no new plutonium is produced from thorium, so the net plutonium consumption level is high.
Integrated thorium mining could be particularly beneficial in closing the critical metals resource gap.[34]. The adoption and expansion of the thorium nuclear fuel cycle should not imperatively require the construction of new mines, because there are many opportunities to recover thorium along with uranium and mainly titanium mining, as well as smaller amounts from tin and iron mining. It is estimated that at least 100,000 tonnes per year could be obtained without the need for new mines. And if all current nuclear power generation were to switch from uranium to thorium, the potential supply via by-products would reach 12 times the amount of thorium required, and 250 times if the reprocessing fuel cycle were implemented.
Ongoing research[35] The first of these looks at the possible application of thorium in heavy water reactorsCandu is the line on which Canadian and Chinese groups are working together. Indian nuclear developers have designed an Advanced Heavy Water Reactor (AHWR) specifically for thorium combustion, capable of 300 MWe of power, approximately 75% of which will come from thorium. The same country has also designed an AHWR300-LEU reactor using low enriched uranium and thorium as fuel capable of providing 39% of the power.
The field of light water reactors is an extremely dynamic one, as another possible option. Norwegian researchers are developing thorium-plutonium oxide (Th-MOX) fuels, which can be used in existing reactors with minimal modifications, thanks to uranium-MOX technology. Hitachi and the Japan Atomic Energy Agency (JAEA) are evaluating the option of using thorium fuels in a water reactor. The thorium reactor Radkowsky has been adapted to Russian-type light water reactors by introducing the design of the seed fuel rods in the central portion typical of Russian naval reactors.
The European Framework Programme has supported three irradiation tests with thorium-plutonium fuels and, in the United States, the Idaho National Laboratory and the Nuclear Science and Engineering Center at Texas A&M University, together with Clean Core Thorium Energy, have supported three irradiation tests with thorium-plutonium fuels.[36], have collaborated on the development of an Advanced Nuclear Energy for Enriched Life (ANEEL) fuel, which blends Highly Enriched Low Enriched Uranium (HALEU) and thorium.
In molten salt technology, there is renewed interest in thorium-fuelled mass reaction reactors (MSRs). Projects are underway in China, Japan, Russia, France and the United States. It is one of six Generation IV reactor designs.[37] considered worthy of further development. The Shanghai Institute of Applied Physics (SINAP) is driving two lines of work on MSRs, with significant support from the US Department of Energy through the Oak Ridge Laboratory, which is collaborating with the Chinese Academy of Sciences on the programme, with an initial budget of $350 million. Its first major result was the spring 2025 scientific achievement mentioned above, which will result in a 10 MWe (electricity) reactor located near Wuwei in Gansu province from 2030.
When operational, it will also be able to generate hydrogen, as it will be designed to produce 60 MW of thermal energy. In fact, the thorium molten salt system is being considered for non-electric applications, thanks to the high temperatures of the reactor. In case of overheating or power failure, the system uses a plug of frozen salt at the bottom of the reactor vessel that melts automatically, and allows the molten radioactive salt to drain into a secondary cooling chamber.[38]. The environmental impact report of the Chinese Academy of Sciences indicates that the molten salt reactor core will be three metres high and 2.8 metres in diameter.[39]. One of the issues to consider is precisely the corrosive nature of molten salts, which calls for tailor-made alloys such as Hastelloy-N, capable of resisting both radiation and chemical degradation and of operating reliably for decades, at extreme temperatures and in radioactive environments.
At the state level, India's three-stage plan for the thorium cycle, first proposed at the University of Chicago in 1944, is also well known. The country is currently commissioning a fleet of 500 MWe sodium-cooled fast reactors, which will produce the plutonium needed to unlock the energy potential of thorium in its advanced heavy water reactors (AHWRs). This will take 15-20 years, so it will still be some time before it can use thorium energy to any extent. In the final part of the model, India's AHWRs will burn thorium-plutonium fuels and generate U-233, which can eventually be reused as a fissile propellant, as demonstrated in the final reactor core. Shippingport in the USA.
There is no shortage of science and technology-based start-ups that are daring to enter the race to replace uranium in nuclear power plants. Natura Resources[40] and Abilene Christian University (Texas, USA) are collaborating on a one MW molten molten salt liquid reactor. Kairos Power is developing a high-temperature fluoride salt-cooled reactor at Oak Ridge National Laboratory that will use uranium-based tri-structural isotropic particle (TRISO) fuel. The company has signed an agreement with Google to supply a total of 500 MW by 2035 to power its data centres.
Copenhagen Atomics[41] (Denmark) is working on a thorium-based molten salt reactor and plans to weld it so that would-be thieves will have to break into a highly radioactive system if they want to get to the material and use it in weapons. Transmutex received a $23 million investment to develop its thorium reactor concept.[42]. The Swiss start-up builds on decades of work started by Nobel Physics Laureate Carlo Rubbia at CERN in the 1990s.[43]. It combines a particle accelerator called a cyclotron with a lead-cooled subcritical reactor. Transmutex intends to use this investment to develop a complete digital simulation of the entire reactor system to minimise errors during construction. It could build its first reactor within 10 to 12 years.
Copenhagen Atomics is taking a completely different approach, focusing on small molten salt reactors to meet the energy needs of private companies. The modular reactors produce 100 MW of thermal power each, and the company envisages the possibility of combining an unlimited number of units to achieve higher output. Rather than selling the reactors themselves, Copenhagen Atomics' business model allows customers to purchase thermal power as a service, and handles the implementation, operation and decommissioning of the reactors. If the UK adopts its experimental prototype, Copenhagen Atomics wants to build its first commercial reactor in 2028 and deploy additional units with a total capacity of 12 GW by 2035. It estimates that the energy cost savings in the country could be around £8 billion.
The French-Dutch startup Thorizon[44] has announced plans to build a small modular molten salt reactor that will use existing stocks of spent nuclear fuel, mixed with thorium, to produce 100 megawatts of electricity, enough to power 250,000 homes for more than 40 years. Experts estimate that the current stockpile of nuclear waste could supply Europe for more than four decades.
Like Thorizon, French company NAAREA has set out to capitalise on them and is developing the XAMR, a molten salt microreactor designed to generate 40 megawatts of electricity and 80 megawatts of heat using spent fuel from conventional nuclear power plants.[45]. It has signed nearly 30 memoranda of understanding with industrial players, including Automotive Cells Company (ACC), to power its gigafactories for batteries; EO Concept, a subsidiary of Energy Observer, to produce hydrogen and low-carbon fuels for shipping; and Phoenix Manufacture, which seeks to industrialise the reactor from prototype to mass production. In Norway, Thor Energy is testing a thorium fuel for use in existing nuclear power plants. Flibe[46] and ThorCon[47], Terrestrial Energy, for its part, plans to use a thorium-based fuel cycle instead of uranium in its reactors. Terrestrial Energy is also considering operating its reactor as a thorium generator in the future.
Any fuel cycle option considered will require relatively long lead times for implementation: 15-20 years to design, build, permit and commission a new fuel cycle facility; deployment of the first commercial reactor could take several years; and full implementation of a fuel cycle could require a couple of decades to a century to transition from a fleet using a single fuel cycle.
Thorium has raised an interesting debate about its possible impact on nuclear proliferation. In principle, thorium-based power reactor fuels would be a poor source of fissile material usable in the illicit manufacture of an explosive device. The U-233 in spent thorium fuel contains U-232, which decays to produce highly radioactive daughter nuclides, and this makes proliferation more difficult as it creates significant handling problems and greatly enhances the possibility of detection.
Other experts point out, however, that if fuel circulates in and out of the reactor core during operation, this movement facilitates the theft of U-233. A study funded by the National Nuclear Security Administration (NSA) concluded that the by-products of the thorium fuel cycle, in particular U-233, could be an attractive material for the manufacture of nuclear weapons.[48]. And another from Cambridge University also concluded that thorium fuel cycles pose significant proliferation risks.[49].
In addition, the health of miners in the pursuit of thorium resources should also be taken into account.[50]. At the Steenkampskraal mine in South Africa, naturally high concentrations of thorium lead to a high presence of thoron gas. And as for the risk from the waste, a comprehensive DOE study in 2014 revealed that waste from thorium-uranium fuel cycles has similar radioactivity to uranium-plutonium fuel cycles at 100 years, and even higher at 100,000 years.[51].
China is also a pioneer in advanced reactor technologies. High-temperature reactors using gas as a coolant are an area of great interest for China; some reactors using this technology have recently been commissioned, and more are in the planning or construction phase.[52].
IN SPAIN. Advanced industry in a country that is getting off the nuclear train.
Spain's pioneering status in the field of nuclear energy, which gave it the impetus for the plants 50 years ago, has consolidated an industrial fabric with enormous scientific and technological capabilities. With the emergence of uranium-free generation projects, especially those based on thorium and molten salts, it should come as no surprise that a company such as Empresarios Agrupados should sign a contract in 2022 for the engineering development of a Generation IV nuclear power plant (GEN IV) in Indonesia.[53] with 500 MW of power and promoted by ThorCon. The Spanish company is involved in project management, documentation control, regulatory compliance, site preparation, pre-construction activities and licensing agreements, according to Foro Nuclear. In addition, its engineering services will be present from design to construction, operation and decommissioning. ThorCon's TMSR-500 is inspired by the experiments at the US Department of Energy's Oak Ridge National Laboratory, discussed in the previous section, as is the 2 MW molten salt reactor at the Shanghai Institute of Applied Physics. It will be the world's first commercial-scale Molten Salt Reactor.
Spain is not currently developing thorium nuclear power plant projects, but some of its rare earth deposits include this metal, such as Matamulas (Ciudad Real). Among the companies that make up the technology sector with a presence in nuclear energy projects worldwide are the following[54] Amphos 21, EDP EAG (Empresarios Agrupados GHESA), Endesa, ENUSA, Enwesa Equipos Nucleares, Grupo Eulen, Naturgy, Proinso, Ringo Válvulas and Tamoin. They specialise in support services for nuclear facilities, both for operation and maintenance, in more than twenty countries, where they have developed strong technological links. This has provided a mutually beneficial framework through which Spanish industry has been able to participate in the development of nuclear projects all over the world.
The fuel assembly factory at Juzbado (Salamanca) has supplied nearly 30,000 fuel assemblies for both Spanish and foreign nuclear power plants since it began operations in 1985. In the field of capital goods, the sector in Spain produces turbo-alternators, valves, cranes and piping, boilermaking and equipment for fuel handling and storage, mostly for export. Engineering services, meanwhile, range from the supply of simulators to inspection and improvement in operation.
In short, it is an industrial potential with the leadership capacity to adapt to the technological change that could be brought about by the introduction of alternatives to uranium in nuclear energy. In fact, the Spanish nuclear industry participates in international R&D projects on advanced nuclear power plants, small modular reactors (SMRs), nuclear fusion such as the ITER International Project and in programmes related to high-energy physics.
An example of this is the award by the Centre for Technological Development and Innovation (CDTI) to the joint venture formed by Asturfeito, Empresarios Agrupados Internacional and Ingecid of a contract for the development of innovative solutions in the field of validation of fusion energy systems and materials (DONES). Another lot of the VATIST contract is for the development of the technological validator of the test cell of the IFMIF-DONES project (International Fusion Materials Irradiation Facility - DEMO-Oriented Neutron Source), a scientific infrastructure located in Granada and designed to support the development of nuclear fusion energy, a clean, safe and sustainable type of energy. Its main objective is to test and evaluate advanced materials capable of withstanding the extreme conditions inside a nuclear fusion reactor, such as high temperatures and high doses of radiation. Specifically, the scope of the VATIST contract includes the design, manufacturing, assembly and testing of the validator, consisting of the vacuum vessel, the lithium target, the radiation shielding, the service systems and the equipment control system.
[1] Integration of Renewables. Red Eléctrica (Accessed 18/06/2025).
[2] Nuclear power plants in Spain. (2025) Ministry for Ecological Transition and the Demographic Challenge. (Accessed 18/06/2025).
[3] Top 10 Largest Uranium Mines in the World (2020) Nuclear Forum. Available at: (Accessed 18/06/2025).
[4] Verificartve, G.I./ (2025) Uranium in Spain: YES, there are reserves, but by law it cannot be extracted., RTVE.es. (Accessed 18/06/2025).
[5] J. Guillermo Sánchez León / The Conversation. (2024) What We Know About Spain's Only Radioactive Waste Storage Facility, National Geographic Spain. Available at: (Accessed 18/06/2025).
[6] Benke, E. (2023) Finland's plan to Bury spent nuclear fuel for 100,000 years, BBC News. (Accessed 18/06/2025).
[7] New, D. (no date) Solar thermal plants in Spain location and environmental impacts, Engineering education. (Accessed 18/06/2025).
[8] History of Molten Salt Reactors (undated) FHR, UC Berkeley. (Accessed 18/06/2025).
[9] Midgley, E. and the agency, I.A.E. (2025) What are molten salt reactors?, IAEA (Accessed 18/06/2025).
[10] Molten Salt Corrosion in the Service of Energy Technologies: From Renewable to Nuclear (undated) CIC energiGUNE. (Accessed 18/06/2025).
[11] Thorium, World Nuclear Association. (Accessed 18/06/2025).
[12] Advanced Heavy Water Reactor (AHWR) Research & Development Activities - Research Projects:AHWR , BARC. (Accessed 18/06/2025).
[13] Near term and promising long term options for the deployment of thorium based nuclear energy (2022) International Atomic Energy Agency. (Accessed 18/06/2025).
[14] Stephen Chen, “China has world's first operational thorium nuclear reactor thanks to ‘strategic stamina’”, scmp.com, 17 April 2025, accessed 22/05/2025
[15] Stephen Chen, “Chinese shipyard unveils plans for world's first nuclear container powered by cutting-edge molten salt reactor”, SCMP, 5 December 2023.
[16] Artem Vlasov, “Thorium's Long-Term Potential in Nuclear Energy: New IAEA Analysis”, IAEA, 13 March 2023, accessed 22/05/2025
[17] Rajesh Kumar Jyothi et al. An overview of thorium as a prospective natural resource for future energy, Front. Energy Res., 15 May 2023, doi.org/10.3389/fenrg.2023.1132611
[18] Caroline Banton, “4 Clean Energy Alternatives to Uranium”, Investopedia, 12 July 2022, accessed 22/05/2025
[19] “Thorium”, WNA, 2 May 2024, accessed 23/05/2025.
[20] “Thorium-Based Nuclear Reactors, Government of India, 26 June 2019.
[21] The Commanding Heights of Global Transportation, SAFE, March 2021
[22] “Merits and Viability of Different Nuclear Fuel Cycles and Technology Options and the Waste Aspects of Advanced Nuclear Reactors (2023)”, National Academy of Sciences, 2023, DOI: 10.17226/26500
[23] “World thorium occurrences, deposits and resources”, International Atomic Energy Agency, 2019.
[24] Stephen Chen, “China's thorium survey finds ‘endless energy source right under our feet’”, SCMP, 1 March 2025, accessed 23/05/2025
[25] Jesslyn Shields, “Could Thorium Power the Next Generation of Nuclear Reactors?”, howstuffworks.com, 16 April 2024, accessed 23/05/2025
[26] Du Toit, M. H., Cilliers, A. C., Preliminary economic evaluation of thorium-based fuels in PWRs. Nucl. Technol., 2014, doi: 10.13182/NT13-134
[27] Dittmar, M., The future of nuclear energy: Facts and fiction chapter IV: Energy from breeder reactors and from fusion? Phys. Soc., 2018, doi:10.48550/arXiv.0911.2628
[28] Yu, C. et al. Thorium utilization in a small modular molten salt reactor with progressive fuel cycle modes, Int. J. Energy Res. 25 June 2019, doi:10.1002/er.4511
[29] “Large Energy Users Pledge”, WNA, 2025
[30] “The Nuclear Fuel Report”, WNA, 21 May 2024
[31] “Uranium Supply is Not a Significant Constraint to Using Nuclear Energy for Climate Mitigation”, NIA, 18 January 2023.
[32] Thomas E Rehm, Advanced nuclear energy: the safest and most renewable clean energy, Chemical Engineering, March 2023, doi.org/10.1016/j.coche.2022.100878
[33] WNA, 21 May 2024
[34] Ault, T. et al. Assessment of the potential of by-product recovery of thorium to satisfy demands of a future thorium fuel cycle, Nucl. Technol., 22 Mar 2017, doi: 10.13182/NT14-19
[35] WNA, 2 May 2024
[36] Clean Core Thorium Energy
[37] “Generation IV Nuclear Reactors”, WNA, 30 April 2024, accessed 23/05/2025.
[38] “China refuels thorium reactor without shutdown”, Nuclear Engineering International, 22 April 2025, accessed 23/05/2025.
[39] Emily Waltz, Yu-Tzu Chiu, “Why China Is Building a Thorium Molten-Salt Reactor”, IEEE Spectrum, 30 December 2024, accessed 23/05/2025.
[40] https://www.naturaresources.com/
[41] https://www.copenhagenatomics.com/
[42] Victoria Atkinson, “‘It's an efficient machine to destroy nuclear waste’: nuclear future powered by thorium beckons”, Chemistry World, 17 April 2024, accessed 23/05/2025
[43] https://www.nobelprize.org/prizes/physics/1984/rubbia/biographical/
[44] Aman Tripathi, “Europe's firm to use nuclear waste to generate 100 MW power for 250,000 households”, Interesting Engineering, 19 May 2025, accessed 23/05/2025
[45] Aamir Khollam, “France's NAAREA advances 40 MW reactor that uses spent fuel as energy source”, Interesting Engineering, 8 April 2025, accessed 23/05/2025
[46] https://flibe.com/
[47] https://thorconpower.com/
[48] Charles G. Bathke et al. Cycles for Various Proliferation and Theft Scenarios, Nuclear Technology, 2012, doi.org/10.13182/NT10-203
[49] Stephen F. Ashley et al. Thorium fuel has risks, Nature, 5 December 2012, doi.org/10.1038/492031ª.
[50] Lindsay, R. et al. Pilot study of thoron concentration in an underground thorium mine, Health Phys., 1 October 2022, doi: 10.1097/HP.0000000000001598
[51] “Nuclear Fuel Cycle Evaluation and Screening - Final Report”, US Department of Energy, 8 October 2014.
[52] Casey Crownhart, “A long-abandoned US nuclear technology is making a comeback in China”, MIT Technology Review, 1 May 2025.
[53] “Spain's Empresarios Agrupados participates in the world's first commercial molten salt reactor”, Nuclear Forum, 25 February 2022.
[54] “Spanish Nuclear Industry 2025”, Foro Nuclear, 2025