Advanced Nuclear Technologies
Today’s development of a new generation of advanced reactors, often referred to as Generation IV, build on the government-funded R&D that gave us the Generation I reactors in the 1950s and 60s. These reactors can be cooled by molten salts, liquid metals, and high temperature gasses, and they can be either thermal or fast. Advanced nuclear technologies hold the promise of zero-carbon electricity necessary to combat climate change and benefits far beyond those of nuclear reactors used today.
In an era of advanced materials, supercomputing, and modular construction, different options are emerging. A new generation of engineers motivated by climate change is picking up the mantle of innovation from their forebearers and developing advanced reactor designs that can provide clean, reliable power at a competitive price. They are considering how to use coolants other than light water; how to operate at normal atmospheric pressure; how to use physics in addition to engineering to keep reactors safe; and how to make reactors small enough to be mass-produced in factories, significantly slashing construction costs and saving time.
If you’re new to the concept of advanced nuclear, this “library” can help get you up to speed on the basics in no time and includes definitions of key terms used by the pros. If you’d like to go a bit deeper, we’d recommend checking out the World Nuclear Association Information Library or taking a look at the additional resources we’ve provided for each of the following major topics to get you started.
How Different Reactors Work
Fission reactors use the splitting of atoms to generate heat. When an atom is split, it gives off particle radiation and light radiation. Some of the particle radiation is made up of neutrons that go on to further the nuclear reaction by getting absorbed into other atoms. Once absorbed by another atom, the neutron makes the atom that absorbed it unstable, causing the atom to break apart and continuing the chain reaction. Fusion reactors create energy by fusing the nuclei of smaller, lighter atoms into one heavier nucleus. The most well known fusion reaction is that which powers our sun, where two hydrogen atoms fuse into a single helium atom. During this process, some matter is converted into energy.
Fission reactors can be broken down by the way in which the neutrons released during fission are used and are either Fast Reactors or Thermal Reactors. Thermal reactors use moderators like water to slow down neutrons, which allows absorption of the neutron into another atom to happen more easily. Neutrons released during the fission process all start out as fast neutrons but bounce back and forth between the molecules of the moderator and lose lots of their energy, becoming slow or thermal neutrons. Most commercial reactors today are thermal and the vast majority of the 16,000 cumulative reactor-years of experience in operating commercial nuclear power comes from thermal reactors. Fast Reactors use the fast neutrons immediately after the neutrons are released during the fission process.
Nuclear reactors in use today (which account for 20% of the United States’ electricity generation and 60% of its carbon-free electricity generation) are light-water reactors. These traditional reactor types have been used since the 1960s. They use highly pressurized water to cool the reactor core. As a result of these high pressures, the reactor core requires specially made vessels, all of which are manufactured outside the U.S. and only made by a tiny number of global manufacturers. The process of manufacturing this traditional reactor type is slow and costly, a problem advanced nuclear technologies promise to remedy.
Fast breeder or neutron reactors, collectively known in this paper as fast reactors, keep the neutrons moving quickly, which makes the fission reaction more efficient and in some cases can actually breed more nuclear fuel. These reactors can consume the most dangerous waste of light-water reactors, thereby reducing the total quantity of waste requiring deep geologic disposal.
Benefits of Advanced Nuclear Technologies
Developers are working to create reactors with simpler designs, modular construction, scaling, and other innovations to be cost competitive with fossil fuels. A number of the benefits we list here also contribute to lower overall costs, including passive safety systems, increased time between refueling, and improved reliability. Some of the significant cost reductions come from standardardized design and modularization of the plants. According to an EIRP report, the Levelized Cost of Electricity (LCOE) for these plants can be as low as $37/MWh, with an average of $60/MWh. This is significantly less than the $97/MWh of traditional nuclear plants and is competitive with other types of energy generation.
- What Will Advanced Nuclear Plants Cost?
- Westinghouse 3D printing trials reveal cost savings for all reactor types
Some micro-reactors are being designed specifically for the most remote locations—think mining operations, military installations, or isolated villages. These reactors are completely self-contained, generate relatively small amounts of electricity (around 2 to 5 MW), and can be easily brought to remote locations, installed, and left to operate for years at a time without intervention. Such a reactor could power a defense facility, avoiding the costly and often dangerous practice of transporting millions of gallons of liquid fuels over inhospitable terrain or relying on a vulnerable public grid.
- Advanced Microgrids
- The Role of Microgrids in Helping to Advance the Nation’s Energy System
- Assessment of Small Modular Reactor Suitability for Use On or Near Air Force Space Command Installations
While existing reactors need to be refueled every 18 to 24 months and some advanced reactors can operate for as many as 20 years between refueling, there is the potential to develop a reactor that could run essentially in perpetuity. These designs would use innovative fuel cycles or simply the physics of the reactors to reuse the waste produced from the reaction process to operate for as long as a century without having to go offline for a sustained period of time. A handful of developers are working on fusion, rather than fission, reactors. While much more complicated and still far off from commercialization, fusion reactors, which run on hydrogen, could have a nearly unlimited supply of inexpensive fuel, without the problem of waste to manage, recycle, or secure.
- Start-Ups Take On Challenge of Nuclear Fusion
- The Future of the Nuclear Fuel Cycle
- Nuclear researchers seek to extend nuclear fuel life and efficiency through improved fuel pellets
Modern Safety Features
The reactors we use in the United States today have an impressive safety record. Advanced reactors are being designed with features that can allow nuclear to maintain this tradition of excellence, but in a more efficient and cost-effective way. Because many advanced reactor designs do not use high pressure or even water as a coolant, they can rely on the passive physics of the reactor system (rather than active safety systems) to shut the reactor down and remove residual heat in the event of an accident or malfunction. An example is the “plug and drain” system. If a fluid-filled molten salt reactor gets too hot, it will melt a plug located at the bottom of the reactor, and the molten salt will drain down to a catch basin where it will cool on its own. This all happens because of gravity—no pumps, external power, or human intervention is required.
Potential for Decreased Proliferation Risk
Some advanced reactor designs could help lower the risk of proliferation by consuming the plutonium they produce or simply not producing it in significant amounts. These reactors can also take the plutonium stockpiles from countries that have nuclear weapons programs and use that plutonium for power production instead. This would continue the momentum of the Megatons to Megawatts program, where the U.S. purchased approximately 20,000 nuclear bombs worth of excess highly enriched uranium from Russia and used it as fuel for American civilian nuclear reactors. Other advanced designs can use depleted uranium, the waste remnants of the uranium enrichment process. This would eliminate the need for centrifuges—also required for the production of highly enriched, weapons-grade uranium—and would dramatically reduce the proliferation risk from countries that might attempt to use a civilian nuclear program as cover for military ambitions.
- Megatons to Megawatts: Russian Warheads Fuel U.S. Power Plants
- Generation IV Nuclear Reactors
- The Global Nexus Initiative
Plug & Go
Most civilian reactors currently in operation around the globe need to be refueled every 18 to 24 months. This process requires significant infrastructure to ensure that the refueling is done safely and the spent fuel is secured against accident or theft. Reactors also go offline for about 40 days during the refueling process, costing their operators money and temporarily eliminating a reliable and major source of electricity. Some advanced reactors are being developed to be “plug and go,” meaning that once the reactor is installed on site, it doesn’t need to be refueled for up to twenty years. This extended fuel cycle is a significant benefit to countries that don’t want or cannot afford to build the necessary infrastructure, such as enrichment, fuel fabrication, or nuclear waste facilities. It can also help protect against nuclear fuel being diverted for weapons development.
Managing Nuclear Waste
Spent fuel, a type of nuclear waste, is a challenge for today’s reactor operators and the federal government. While operators are locally storing spent fuel safely, the process is costly and the public remains concerned about the continued production of this type of nuclear waste, which lasts for thousands of years. Many advanced reactor designs have the potential to address these concerns by actually consuming spent fuel, dramatically reducing the amount of waste requiring storage. Other advanced reactors, breeder reactors, would help manage nuclear waste by using fuel much more efficiently than current reactors and by actually creating new nuclear fuel. This could significantly reduce the real but manageable environmental challenges caused by trying to store spent nuclear fuel for centuries.
Today, fossil fuels create the high temperatures needed for industrial applications, which are used in sectors such as chemicals, food processing, and cement. This results in a portion of the approximately 1,400 megatons of direct greenhouse gas emissions annually in the U.S. alone. Renewables and existing nuclear reactors cannot efficiently produce the high temperatures needed to replace these furnaces. Some advanced reactors would safely operate at temperatures high enough to supplant fossil fuels in industrial processes and to produce electricity as well.
- Sources of Greenhouse Gas Emissions: Industry Sector Emissions
- Advanced Nuclear Technologies can Help Achieve a Carbon-Free Energy Future
Some reactors are classified as advanced simply because of their size. Today, most reactors are built to generate between 1000 and 1200 MW of electricity. The majority of markets in the developed world do not need additional electricity at that scale. Advanced nuclear developers are designing small modular reactors and micro-reactors, which are designed to generate between 2 and 200 MW per reactor. These small modular and micro-reactors could be built in a factory and then shipped to the construction site for a relatively quick installation. Because of their modular design, operators can scale the power plant to meet their changing needs, adding new reactors quickly, cost effectively, and in smaller generation increments as demand grows. The modular design also has the potential to reduce security demands on the operator, as the footprint of the site could be much smaller than today’s power plants. Many of the advanced reactor designs are also intended to be installed underground, making them smaller, harder targets for a terrorist or other attack.