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Nuclear power technology development

Updated Monday, 19 January 2026

Most reactors in use today are based around pressurized water reactor (PWR) or boiling water reactor (BWR) designs, with capacities more than 1000 MWe. They use water cooling and operate at around 300 °C.
However, there is increasing interest in a wider range of range of reactor sizes and designs to meet a more diverse range of applications and provide more options for deployment.
New reactor designs are being developed for a range of different capacities, from below 1 MWe to more than 1700 MWe, allowing nuclear technologies to be applied to a wide range of applications.
Designs in development will use gases, molten salts and liquid metals for cooling, which will enable reactors to operate at higher temperatures, and be used for new applications.
Most nuclear reactors currently planned and proposed are intended to be used primarily for electricity generation. However, the use of nuclear technologies for marine propulsion, direct to end user power, district heating, provision of high temperature process heat, desalination, energy storage, hydrogen production and sustainable aviation fuel production is likely to increase in the coming decades, particularly if political commitments to clean energy are pursued and strengthened.
This chapter illustrates how reactors can be categorized by size and coolant used and then illustrates some of the new uses to which new reactor technology is being applied.

2.1 How are reactors categorized by size?

2.1.1 Large reactors

Since the start of nuclear generation in the 1950s the average size of nuclear reactors has tended to increase, as reactor designers sought to improve economies of scale. Some early reactors had relatively small capacities, of similar capacities to those designs classed as small modular reactors today. Most large reactors designs available for construction now have a capacity of 1000 MWe or higher.

Large reactors make up most reactors in use today, and almost all those reactors are water-cooled. A small number of liquid metal-cooled fast reactors have also been constructed. The UK also deployed two types of gas-cooled reactors, the Magnox and AGR series. All Magnox reactors are shutdown, and the last of the AGRs are expected to close by around 2030.

While most large reactors in use today are used for grid electricity production, around 15% also provide district heating.

2.1.2 Small modular reactors

Small modular reactors (SMRs) are nuclear reactors designed for smaller scale power generation. In addition to their size, they are characterized by their modular design, which allows for factory fabrication. According to the International Atomic Energy Agency, SMR designs are typically up to 300 MWe, although larger designs, such as the 470 MWe Rolls-Royce SMR also may have a highly modular design.

Some SMR designs are also based on water-cooled systems, with SMR variants of PWR, BWR and PHWR designs. However, other designs are based on gas, liquid metal, or molten salt systems, and have the potential to provide additional services, such as the provision of high temperature process heat.

2.1.3 Microreactors

Microreactors are compact nuclear reactors, designed to be produced in factories and small enough to be transported by lorry to their deployment site, making them suitable for remote locations. They have much lower power outputs than conventional large reactors or SMRs. This lower power output means that the reactors can rely on fully passive cooling systems.

2.2 How are reactors categorized based on coolant used?

2.2.1 Water-cooled reactors

Water-cooled reactors use water as a primary coolant as well as a moderator. There are three main types – pressurized water reactors, boiling water reactors and pressurized heavy water reactors.

With output heat of around 300 °C these reactors can be used for electricity generation, district heating and low temperature process heat applications. While most water-cooled reactors are large, smaller designs are being developed.

Advanced large water-cooled reactors are evolutions of previous designs, incorporating new technologies. Modular construction approaches are also favoured to reduce building times.

Many water-cooled SMRs are scaled down versions of widely deployed gigawatt-scale light water reactor plants, with an emphasis placed upon modularization, scalability and factory manufacture. Several light water small modular reactor designs feature integral reactor modules for which the key components such as steam generators, the pressurizer and the reactor core are contained within the same single module.

2.2.2 Gas-cooled reactors

High-temperature gas-cooled reactors (HTGRs) operate at significantly higher temperatures than traditional water-cooled reactors, with outlet temperatures from 500 °C to 950 °C. They typically use helium as the coolant, as it does not react with other materials in the core.

The high-temperature heat produced by these reactors will enable nuclear technology to decarbonize hard-to-abate industries such as steel, chemical and concrete production, which currently rely on fossil fuels for process heat. An eventual development of such technology would be the very high temperature reactor (VHTR), able to operate at temperatures exceeding 1000 °C, for high temperature applications above those targeted by HTGRs.

These advanced reactors are being developed at capacities suited for SMRs and microreactors.

2.2.3 Liquid metal-cooled reactors

Fast neutron reactors cooled with liquid metal, usually sodium or lead are reactors without moderators that use high energy neutrons to split atoms rather than slower thermal neutrons used in most commercial power plants. Liquid metal-cooled fast reactors also have efficiency benefits as their use of fast neutrons increases the amount of energy that can be extracted from their nuclear fuel and reduces the amount of long-lived waste generated.

2.2.4 Molten salt reactors

Molten salt reactors use a mixture of molten salts as their primary circuit coolant; fuel can either be dissolved within the coolant or contained within pins. The use of molten salt enables the reactors to operate at lower pressures to traditional commercial nuclear plants. The higher temperatures found within their cores also enable decarbonization solutions, similarly to high temperature reactors. Some molten salt reactors are designed to operate as fast neutron reactors, so have the potential to reduce waste outputs.

Table 2.1 Characteristics of reactor designs based on coolant type and capacity

Coolant	Water			Gas		Liquid Metal (Sodium or Lead)	Molten Salt
Process	PWR	BWR	PHWR	HTGR	Gas Fast Reactor	Fast Reactor	Fluoride HTR	Chloride Fast Reactor
Fuel Enrichment	LEU, LEU+	LEU, LEU+	Natural U or VLEU	HALEU	HALEU	HALEU	HALEU	HALEU
Outlet Temperature	~300 C	~285 C	~300 C	~750 C	~550 C	~550 C	~750 C	~750 C
Large	AP1000	ABWR	Monark			BN-1200
Reactor designs	EPR / EPR2 APR1400	ESBWR	PHWR-700			CFR-600 PFBR
	VVER-1000/
	1200/TOI
	Hualong One/
	HPR1000
	SRZ-1200
Small Modular Reactor designs	Holtec SMR-300 NuScale Power Module AP300	BWRX-300	BSMR-200	Xe-100 HTR-PM (China)	EM2 (850C)	Terrapower-Natrium ARC-100 (510C)	Kairos Power FHR (650 C) Terrestrial IMSR (700 C)	Terrapower MCFR
	Rolls-Royce SMR					BREST-300
	ACP100					SSR-W
	RITM-200N/S
	Nuward
Micro Modular Reactors	KLT-40S			BANR Jimmy Radiant-Kaleidos		Oklo Newcleo-LFR-AS-30
				eVinci (Heatpipe)

2.3 Applications of nuclear technology – grid electricity supply

Nuclear reactors have been supplying electricity to grids for more than 70 years. The 5 MWe AM-1 (Atom Mirny, ‘Peaceful Atom’) reactor at Obninsk first supplied electricity to the Moscow grid in June 1954, with reactors in France, the UK, and the USA following soon after.

As discussed in Chapter 1, growth in nuclear generation accelerated during the 1970s and 1980s, with the global share of electricity supplied by nuclear generation reaching 17% in the mid-1980s.

While growth in nuclear generation has slowed, global generation in 2024 achieved a new high, with 2667 TWh of electricity supply. There has been particularly strong growth in Asia over the last decade, with nuclear electricity generation more than doubling, from 402 TWh in 2015 to 811 TWh in 2024.

While the use of nuclear technology for non-electric applications is expected to grow, grid electricity supply is expected to remain the predominant use of nuclear technology.

2.4 Applications of nuclear technology – non-electric nuclear applications

Nuclear technology has been used in several power applications besides grid electricity supply for more than 70 years. The first nuclear-powered submarine – the USS Nautilus (SSN-571) – was launched in 1954. Calder Hall, the UK’s first nuclear power plant, which started up in 1956, supplied steam to the Windscale (later Sellafield) site, as well as generating electricity for grid supply. More than 40 reactors worldwide have supplied district heating systems.

With growing demand for decarbonization, new applications for nuclear reactors are being developed.

2.4.1 Marine propulsion

Nuclear powered marine propulsion has historically been mostly limited to naval vessels and icebreakers. A new interest in nuclear power is arising from the commercial shipping sector following the International Maritime Organization’s 2023 Greenhouse Gas Strategy, which demands a reduction across international shipping in carbon emissions of at least 40% by 2030 (compared to 2008 levels) and to reach net zero emissions by 2050.

Advanced nuclear reactors to power emissions-free shipping freighters are being developed, such as Core Power’s Molten Chloride Fast Reactor, which is designed to improve on insurability and emergency preparedness zones, compared to the PWRs that have so far been used to power naval vessels. There is currently no precedent for insuring a mobile commercial nuclear power plant, or liability regime for moving a reactor from one jurisdiction to another.

The Sibir, a nuclear-powered icebreaker (Image: Rosatom)

2.4.2 Direct to end user power

Small modular reactors and microreactors can provide remote facilities with a direct supply of electricity, without connecting to the grid. This enables remote industrial operations such as mining facilities to decarbonize their operations without installing an expensive link to the grid. Data centre owners have also started looking to small reactors and microreactors to support their operations as they require large amounts of constant power which corporate sustainability policies require to be as low carbon as possible. With larger data centres larger capacity reactors may be preferred. With the significant growth of this sector, which currently accounts for 1-1.5%of global electricity use, forecast over coming years, there is a need to ensure it is supplied with decarbonized, reliable power.

Nuclear power is also being considered for extra-terrestrial applications, with companies such as Rolls-Royce and BWXT developing reactors for lunar and Martian deployment.

Increased demand from data centres

The rapid emergence of AI over recent years has highlighted how digitization and technological growth is leading to increased electricity demand from data centres. Companies such as Meta, Amazon Google and Microsoft are all looking to nuclear energy to help supply their growing demand for electricity from low-carbon sources.

The global electricity demand from data centres is expected to increase rapidly over the next 5-10 years. The IEA projects that global electricity demand will more than double, from 415 TWh in 2024 to 945 TWh in 2030 and 1300 TWh in 2035, according to their base case scenario. Of this around 220 TWh is projected to be supplied by nuclear power.¹²

Nuclear is well suited to supplying power to data centres, providing firm, clean power with high reliability. With some data centres requiring gigawatts of power, nuclear is also scalable to meet these needs.A number of technology companies have already invested in nuclear technology to meet their future energy needs. While the IEA expect new nuclear capacity to be focused on meeting additional demand post-2030, another option is to secure the output of existing nuclear capacity, including plants that have recently shut down, some examples of such agreements are summarized below:

Microsoft have agreed a 20-year power purchase agreement with Constellation to enable the restart of the 880 MWe (gross) TMI 1, now named the Crane Clean Energy Center.¹³
Amazon (AWS) have a long-term power purchase agreement with Talen Energy for nuclear power to support the AWS data centre near Susquehanna nuclear plant. The delivery is initially 960 MW for AWS, with a ramp schedule of 840–1,200 MW by 2029; 1,680–1,920 MW by 2032; and then full capacity through to 2042, with options to extend the duration of the agreement.¹⁴
Amazon is investing, with off-take rights, to support the development of X-Energy’s Xe-100 SMR at Energy Northwest’s Columbia site. Initially there will be four Xe-100 modules, with a capacity of ~320 MW, with the option to expand this up to twelve modules.¹⁵
Amazon has also signed an MOU with Dominion Energy to explore SMR development at the North Anna site.¹⁶
Meta has signed a 20-year power purchase agreement with Constellation for 1,121 MW from the Climate Clean Energy Centre in Illinois.¹⁷
Google is collaborating with Kairos Power and TVA for the supply of power from Kairos’s Hermes demonstration plant.¹⁸ In October 2024 Google signed an agreement with Kairos Power to purchase energy from small modular reactors, which will support the deployment of Kairos Power's molten salt-cooled reactor using ceramic pebble-type fuel by 2030 and a fleet totalling 500 MWe of capacity by 2035 .
TerraPower and US data centre developer Sabey Data Centers have signed a memorandum of understanding to explore the deployment of Natrium power plants at current and future data centres.¹⁹
Equinix, a data centre operator, has signed agreements with Oklo and Radiant in the US, as well as ULC-Energy and Stellaria in Europe.²⁰
Holtec, EDF and Tritax plan to develop advanced data centres power by SMRs at the former Cottam coal-fired power plant in the UK. This was announced as part of the Atlantic Partnership for Advanced Nuclear Energy announced by the UK and US governments in September 2025.²¹

2.4.3 District heating

Nuclear district heating involves using heat generated by a nuclear power plant to provide warmth to residential, commercial, or industrial areas. The heat is collected via the condenser used to cool the steam leaving the turbine and fed into the district heating system rather than into cooling towers or bodies of water. Using nuclear power to heat buildings in this way reduces the need for fossil fuel powered boilers, reducing emissions and improving air quality in urban areas. Additionally, hot water can be piped over long distances from the plants to where it is needed, with low heat loss.

District heating has been provided by conventional nuclear power plants in Russia and Switzerland for several decades. More recently, the Haiyang nuclear power plant in Shandong province, China, supplies steam from its two AP1000 units, which is then fed through an onsite heat exchanger. This heat is then fed to an offsite heat exchange station belonging to Fengyuan Thermal Power, from where heated water flows through municipal heating pipes to consumers over an area of 13 million square metres.

2.4.4 High-temperature process heat

Some advanced nuclear power reactors designs are intended to provide heat above 700 °C. This would enable them to supply industrial facilities with the heat they require for processes such as the manufacture of concrete, steel, paper, chemicals and glass that are currently provided by fossil fuels or other unsustainable means. Interest in high temperature reactors to decarbonize these processes has grown substantially.

Shidaowan, in Shandong province, features two small reactors (each 250 MWt) that drive a single 210 MWe steam turbine. It uses helium as coolant and graphite as moderator. Each reactor is loaded with more than 400,000 spherical fuel elements (‘pebbles’), each 60 mm in diameter and containing 7 g of fuel enriched to 8.5%. The HTR-PM is expected to be followed by the HTR-PM600 , with one turbine rated at 650 MWe driven by three twin-reactor units.

In the USA, Dow Chemical is working with X-energy to deploy HTGRs at its Seadrift site in Texas, and in northeast UK, X-energy is seeking to develop its reactors to support an industrial site. In France, Jimmy is looking to build its high-temperature microreactor to supply a distillery with process heat.

The High Temperature Gas-Cooled Reactor – Pebble-bed Module (HTR-PM) in Shidaowan, in Shandong province, features two small reactors (each 250 MWt) that drive a single 210 MWe steam turbine. It uses helium as coolant and graphite as moderator. Each reactor is loaded with more than 400,000 spherical fuel elements (‘pebbles’), each 60 mm in diameter and containing 7 g of fuel enriched to 8.5%. The HTR-PM is expected to be followed by the HTR-PM600 , with one turbine rated at 650 MWe driven by three twin-reactor units.

2.4.5 Desalination

There are more than 20,000 desalination plants in operation globally, the majority of which are powered by fossil fuels.²² Two methods of desalination can be facilitated by nuclear power: distillation and reverse osmosis. For distillation, heat from a nuclear reactor is used to boil seawater, which is then condensed, separating the salts and impurities from the water. For reverse osmosis, electric power produced by a reactor is used to pump seawater at very high pressure through a semi-permeable membrane which allows water molecules to pass through while blocking the passage of salts and other impurities. The widespread use of nuclear power in desalination would decarbonize this energy-intensive process.

Nuclear powered desalination has been used in India, Japan, Kazakhstan and Pakistan and new projects have been proposed in Saudi Arabia, South Africa and the USA.²³ Some of the output from the reactors under construction at El Dabaa in Egypt is planned to be used to power desalination plants. Nuclear reactors powering navy vessels have been used to produce clean water for use on the vessels, and have been used to provide water to areas affected by natural disasters.^24, ²⁵

2.4.6 Energy storage

Some advanced nuclear reactors have been designed specifically for energy storage. Reactors such as the MoltexFLEX reactor in the UK and TerraPower’s Natrium plant in the USA have thermal storage tanks that can deliver power when required. The reactor can therefore either deliver power to the grid or to its storage tanks depending on demand.

2.4.7 Hydrogen production

Hydrogen is considered to be a key component of future energy systems due to its ability to be used as a fuel, in the production of fuels and as a replacement for high-carbon compounds in industrial processes such as coke in steelmaking.

Nuclear reactors can be used to produce hydrogen through electrolysis. For example, the Bay Hydrogen Hub project aims to use a small amount of heat from the Heysham II nuclear plant to a solid oxide electrolyzer cell (SOEC) to produce hydrogen.²⁶

Advanced high temperature nuclear technologies would be able to produce hydrogen through thermochemical reactions by providing the high temperature heat required.

2.4.8 Sustainable aviation fuel

Sustainable aviation fuel (SAF) has the potential of reducing carbon emissions from aircraft by up to 80% compared to traditional jet fuel and therefore provides a solution to one of the hardest sectors to decarbonize. Advanced nuclear power could supply the high temperature heat required for the synthesis of SAF.

2.4.9 Floating nuclear power plants

While a floating nuclear power plant is type of nuclear energy installation, rather than an application, such a plant can deployed in situations where it may not be preferable to build a land-based plant.

A floating nuclear power plant consists of a nuclear reactor installed onto a barge that would then be towed to its deployment location, where it could be connected to provide power, heat or other services, such as supply of potable water through desalination.

Floating nuclear power plants have the potential to benefit from the scaling and series production offered by shipyard construction. They should also require less infrastructure to be established at their eventual deployment location.

It may be possible to deploy floating nuclear power plants more rapidly than siting an equivalent reactor on land, as fewer site-specific constraints would be involved.

The only floating nuclear power plant currently in operation is Rosatom’s Akademik Lomonosov, which is located at the Russian port of Pevek, in northeast Russia, where its two KLT-40S reactors provide power and heat to the region.

Four RITM-200S floating nuclear power reactors are under construction, with the reactors to supply power to the Baimskaya mine in northeast Russia. The reactors are being manufactured in Russia, with the vessels being built at a shipyard in China.²⁷

Several companies are currently developing their own floating nuclear power plant offerings with a variety of technologies, including light water reactors and molten salt reactors. These include Core Power, KEPCO E&C’s BANDI, Saltfoss Energys’ CMSR power barge and Prodigy Clean Energy’s nuclear barge, which is designed to accommodate SMRs from other vendors.

Floating nuclear power plant Akademik Lomonosov (Image: Rosatom)

It may be possible to deploy floating nuclear power plants more rapidly than siting an equivalent reactor on land, as fewer site-specific constraints would be involved.