What is Advanced Nuclear Technology?

Key Takeaways

New nuclear reactor designs are on the horizon that are fundamentally different from those we operate today.
Innovators are looking for ways to decarbonize with nuclear power that is safer, cheaper, more efficient, and more versatile than ever before.
Modular reactor designs may significantly reduce nuclear construction costs and timelines, allowing reactors to be built in factories and shipped to site.
Other innovations in fabrication and manufacturing techniques may enable advanced reactor production, construction, and operation to be more efficient and cost-effective.
Advanced nuclear reactor designs are still being demonstrated, and are estimated to be ready for commercial-scale deployment within the next decade.

Advanced nuclear technologies represent innovations in the production of electricity through nuclear power. These technologies have distinct differences and advantages over traditional nuclear power plants, which are almost exclusively light-water and heavy-water reactors used for large-scale baseload electricity generation. These innovations are typically seen in the design of advanced reactors, such as small modular reactors (SMRs), non-water cooled reactors, and microreactors. Additional non-reactor advanced technologies can help to revolutionize the nuclear industry. These include novel fabrication methods for nuclear reactor parts, new uses for robotics, high-fidelity data models, and more. In this article, we’ll take a closer look at several designs for advanced nuclear reactors, their advantages over current reactor designs, and non-reactor advanced nuclear technologies.

Advantages of Advanced Nuclear Technologies

While renewable energy is sure to play a major role in decarbonization, most experts believe that nuclear energy must contribute as well. Traditional nuclear reactors have had challenges to on-time deployment in part related to their large scale. As utilities look for smaller options that can be easier to finance and build, many advanced nuclear technologies hold significant promise.

What Are the Advantages of Advanced Nuclear Reactors?

Advanced nuclear reactors, like their predecessors, split atoms using fission to release energy. Fission is completely carbon-neutral, and the energy can be harnessed to generate electricity without emissions. While today’s reactors are typically large, baseload electricity generation facilities, future reactors may be smaller and have a wider range of uses. Here are some of the advantages of tomorrow’s reactor designs.

Cogeneration with Advanced Nuclear Reactors

While today’s nuclear reactors generally only produce electricity, future reactors may simultaneously produce heat and electricity, called cogeneration. This expands the uses for nuclear power significantly and could raise efficiencies to 80%.

Applications of Advanced Nuclear Reactors Beyond Electricity

Advanced nuclear reactor designs often use higher temperatures, making them more viable for non-electric applications such as desalination, hydrogen production, and district and industrial heating. Many advanced reactor designs also have inherent safety features and can be sited closer to densely populated areas, allowing greater efficiency to supply heat for industrial processes. In the past, nuclear energy has had limited potential to decarbonize sectors other than electricity. With cogeneration, nuclear energy can be used to generate heat to decarbonize the industrial or residential sectors. It could also be used to generate hydrogen and other liquid fuels, which could help decarbonize the transportation sector.

Advanced Nuclear Reactors are Safer

To respond to public concerns about the safety of nuclear energy, advanced nuclear reactors are designed to be inherently safer than the reactors used today, which have minimal risks to start with. Advanced reactor designs vary significantly, but most incorporate inherent safety features that reduce or eliminate the risk of contamination. For example, in the event of a power outage or complete loss of cooling systems, NuScale’s SMR could safely shut itself down. This prevents damage to the nuclear fuel and stops the possibility that radioactivity will spread. Most advanced nuclear reactor designs are smaller than reactors today. With less heat produced, they are easier to design for complete safety under all circumstances. Many also function at ambient pressure, reducing the potential for higher energy accidents. The use of advanced fuels that contain fission products helps to reduce the requirement for large containment structures.

Versatility and Flexibility

To meet the needs of tomorrow’s electricity grid, advanced nuclear reactor designs often can be operated with variable electricity generation for load-following. In other words, they could produce a small amount of power when demand is low, or be ramped up to produce larger amounts of power to meet high demand. In contrast, today’s reactors almost exclusively operate at full power and have limited ability to adapt to variable demand. Since advanced reactor designs are typically smaller than today’s large-scale, 1 GW reactors, they have a greater landscape of potential uses. For example, microreactors have been studied as potential power sources to replace diesel generators in military bases, mining operations, and remote settlements.

Modularity

Many advanced reactors have modular designs, meaning that all, or most of, the reactor can be fabricated in a factory and shipped to its end-use site. This can significantly reduce construction timelines and costs, which are the largest drivers of project risk for traditional nuclear plants. Modularity may make it cheaper and faster to scale nuclear power to meet significantly greater energy needs.

Waste-Burning

Some advanced nuclear reactor designs use a fast neutron spectrum which doesn’t require a neutron moderator like current plant designs. This means that the neutrons in the reactor have higher energy levels than today’s reactors. With these higher energy neutrons, the reactor is able to fission essentially all actinide isotopes — including the major components of nuclear waste in the form of spent nuclear fuel. Waste-burning fast reactors can recycle nuclear waste to significantly reduce its quantity and long-term toxicity, all while generating power.

Types of Advanced Nuclear Reactors

Advanced nuclear technology comes in a variety of forms. Broadly, advanced nuclear reactors have different power capacities, fuel forms, moderators, coolants, and/or neutron spectra than today’s reactors, but they all use nuclear fission to produce emissions-free energy. Here are a few of the major categories of advanced nuclear reactors, and some advantages of each.

Small Modular Reactors (SMRs)

Small modular reactors (SMRs), often used to refer to light-water SMRs, are most similar to today’s nuclear reactors since they use liquid water as both a coolant and moderator to fission uranium fuel. However, small modular reactors are significantly smaller and have the potential to make nuclear energy more economical using modular construction. Another advantage of SMRs comes from their smaller size. They consequently cover much less land with their emergency planning zone (EPZ). With inherent safety measures that decrease the possibility of an accident, these plants can be placed closer to densely populated cities and industrial zones, providing greater opportunities for cogeneration and heat applications beyond electricity.

Molten Salt Reactors

Molten salt reactors often use chemical salts such as fluorine or chlorine, which are both mostly neutron-transparent, as their coolant. The uranium fuel can be introduced as a solid (in the form of TRISO fuel, for example) or dissolved directly in the liquid salt fuel. Both options allow the reactor to refuel without shutdown, also called online refueling. Online refueling and fission product removal in the dissolved fuel design could significantly reduce maintenance and waste costs. Molten salts have relatively low melting temperatures but high boiling points. This means they can operate at ambient pressure, a safety feature that decreases risks of pressurized pipe failure. Freeze plugs could also be used to drain the reactor core above a certain temperature. These are actively cooled segments of pipe that solidify a piece of the salt in the core. When the temperature gets too high, it overwhelms the cooling, melting the plug and draining the core into safe storage basins to stop the chain reaction. Dissolved fuel molten salt reactors come with additional inherent safety features. Thermal expansion can passively cause reactor shutdown by volumetrically decreasing criticality. In other words, if the coolant gets too hot, the expanding salt moves the dissolved fuel molecules farther apart, slowing the chain reaction down. Since the fuel is dissolved into the salt directly, fuel melting is impossible and presents no risk, which is one of the major accident scenarios to avoid in a solid-fueled design.

Liquid Metal Fast Reactors

Liquid metal fast reactors will typically use metallic sodium, lead, or a lead-bismuth mixture as their coolant. Due to the lack of moderating potential these metal fuels have, they enable operation with a high-energy fast neutron spectrum. Some designs are capable of burning nuclear waste as fuel, as the fast neutrons are able to induce fission in uranium-238 and the many transuranic isotopes. Similar to molten salt reactors, the low melting point and relatively high boiling point of liquid metal fast reactors allows for operating at near ambient pressures. This reduces the potential for accidents. Liquid metal reactors have excellent heat-transfer and neutronic properties to operate efficiently, potentially burn nuclear wastes, and enhance nuclear safety.

High-Temperature Gas Reactors (HTGRs)

HTGRs use helium gas coolants with a graphite moderator. Helium is the favored gas in HTGRs because it is chemically inert, reducing corrosion in the primary loop. Using gas coolants allows for higher coolant temperatures. Some designs propose operating temperatures around 1000 degrees Celsius. Helium coolant in a closed secondary loop could be run to a turbine up to a temperature of 850 degrees Celsius, allowing for the high efficiency helium Brayton cycles to produce electricity. These electricity generation methods can reach 45% efficiency compared to today’s 33%. One HTGR design variant is the pebble bed reactor. This reactor uses TRISO fuel made of small kernels of uranium encased in carbon and ceramics. The TRISO kernels are embedded in graphite spheres, about the size of a billiard ball. This fuel allows online refueling and contains fission products, making waste management much easier. Another HTGR variant is the prismatic block type. This variant uses the same TRISO kernels as the pebble bed, but forms them into compacts closer to a pellet of traditional reactor fuel. These pellets stack into hexagonal prismatic blocks which form the majority of the reactor core.

Microreactors

Most of the advanced reactor designs discussed so far have had smaller power outputs than traditional reactors, from 50 MW to around 300. Microreactors are advanced reactor designs with power outputs of around 50 MW or less. These reactors are ideal for replacing generators and operating in remote areas. They can be made with a variety of materials, fuels, neutron spectra, and coolants to generate a continuous flow of electricity for years or even decades — without ever refueling. Portable microreactors that have long lifetimes without refueling could be an excellent way to decarbonize a greater portion of the many remote human settlements. They are simple to operate and are designed to not require maintenance for years or decades.

Have Any Advanced Nuclear Reactors Been Built?

Advanced reactor designs are still emerging. Many designs will be demonstrated in the next ten years and could be deployed at scale in the 2030s. Ontario Power Generation in Canada is pursuing a project to build a series of GE-Hitachi BWRx-300 SMRs within the province. In China, the HTR-PM entered operation in 2022, producing electricity for the grid using a HTGR fueled with TRISO pebbles. A liquid fluoride thorium MSR demonstration reactor entered operation in 2023 at a research complex. Similarly, the Advanced Reactor Demonstration Program has allocated significant funds from the U.S. Department of Energy to help construct pilot plants of several different advanced reactor designs. These include TerraPower’s sodium fast reactor, X-energy’s HTGR, and more.

Non-Reactor Advanced Nuclear Technology

At EPRI, we also look for innovations that support growth in the nuclear energy industry aside from reactors. We’ve studied several advanced fabrication methods that have the potential to significantly lower nuclear power plant construction costs and timelines, especially for advanced reactors. These methods include:

Electron beam welding
Bulk additive manufacturing
Powder metallurgy-hot isostatic pressing (PM-HIP)

We’ve also studied a diverse range of applications of robot and drone technologies that could be used to reduce the operations and maintenance costs of existing reactors, making them more economically competitive. Beyond reactors, several advanced technologies will continue to innovate the industry in parallel — and EPRI seeks to find and highlight helpful solutions.

This article is one of many developed by EPRI’s Advanced Nuclear Technology program. Stay up-to-date on the newest nuclear technologies by becoming a member today.