Nuclear Fission: “It’s the only carbon-free energy source that can reliably deliver power day and night, through every season, almost anywhere on earth, that has been proven to work on a large scale. No other clean energy source even comes close to what nuclear already provides today.” – Bill Gates in “How to Avoid a Climate Disaster”
Indeed, nuclear power plants provide 20% of the electricity consumed in the United States with extreme reliability, turned on and providing significant power over 90% of the time. This performance exceeds, on average, that achieved with almost all other forms of electricity generation. The safety record in the United States is also remarkably good, with no harm to operators or the public.
In the United States we are now entering a new era, dominated by the existential risks posed by climate change and the urgent need to eliminate greenhouse gas emissions. In the next decades, solar, wind and nuclear will all play a major role. If done properly, these three technologies can be integrated to form an overall system that is superior in performance, cost and value to that achievable with only one. Detailed studies by utilities that must comply with new decarbonization mandates, as well as others, have shown that nuclear is essential to the achievement of an “always on” cost-effective electricity supply, including cases with energy storage for use with the intermittent wind and solar sources.
The nuclear light water reactors in use today have provided reliable baseload power for several decades. However, after a long period of evolutionary improvement, the technology has finally reached basic limits of performance, and thus value, to the utility systems of the future.
Natrium nuclear power plants represent a significant advance over the light water reactor plants in use today. The Natrium plant uses a sodium-cooled fast reactor as a heat source. This heat from the reactor is carried by molten salt from inside the nuclear island to heat storage tanks outside the reactor building, where it is utilized as needed for generating electricity or industrial processes. The net effect is that the overall plant can load follow, thus increasing the revenue and value of the plant while maintaining the optimum constant reactor power. At the same time the cost of the overall plant is reduced since many of the systems outside of the nuclear island need not be nuclear safety grade. The Natrium reactor enables these abilities because it operates in much higher temperature regimes than the light water reactor, thus pairing well to the temperature requirements of the molten salt heat transfer medium.
Natrium reactors are uranium fueled. No Natrium reactor—from the demonstration plant, to the first set of commercial plants, or the subsequent larger plants—will use plutonium as a fuel. Both the demonstration plant and the first set of commercial plants will run on high-assay low-enriched uranium (HALEU). Natrium plants will not require reprocessing and will run on a once-through fuel cycle that limits the risk of weapons proliferation. Natrium technology will, nonetheless, reduce the volume of waste per megawatt hour of energy produced at the back end of the fuel cycle, by five times, without any reprocessing because of the efficiency with which it uses the fuel.
TerraPower plans to build the 345 MWe Advanced Reactor Demonstration Program (ARDP) demonstration reactor with an integrated energy storage system and to market subsequent commercial reactors with a similar design and size.
Depending upon market conditions, future generations of Natrium reactors could be larger designs, up to the GW scale. Doing so could allow the reactors to take advantage of the benefits of “breed-and-burn” designs that would allow the plants to be refueled with natural unenriched uranium or even depleted uranium. By enabling refueling to occur with these enrichment plant wastes or unenriched materials, the risk of proliferation from exported reactors is further reduced. Inside the reactor core, the reactor does convert some U-238 into a fissile isotope (Pu-239), which it then uses as fuel with uniquely high efficiency before removal. This is the same basic process that occurs in the current generation of light water pressurized reactors, which have been successfully exported around the world.
From its beginnings over a decade ago, TerraPower has made reduction of weapons risks a foundational principle. Ethical global exportability is one of the keys to addressing human poverty and climate change. With the participation of retired weapons laboratory directors and their expert personnel, TerraPower laid out the once-through fuel cycle approach that avoids reprocessing, keeps used fuel intact and countable, makes fuel reloads a rare, monitorable event, and eventually reduces need for enrichment plants. The simplified total fuel infrastructure also reduces the opportunities for theft, terrorist actions or accidents during fuel transport by an order of magnitude relative to reprocessing-based approaches.
The Natrium design introduces many new inherent safety features that prevent accidents. No pumps and emergency power are needed to maintain safe conditions after shutdown. The reactor has what is called a global negative temperature coefficient and automatically seeks safe low power conditions in the case of an unexpected high temperature excursion. This has been shown theoretically and experimentally for a sodium-cooled reactor using metal fuel. An unrecognized but very important feature of the reactor is that it operates at very low internal pressures, thus simplifying the fabrication of the vessel and other components as well as reducing the consequences of any component failure. The design offers several additional safety features, but the net implication is that large exclusion zones are no longer needed and siting options greatly expanded.
The first generation 345 MWe Natrium reactors will use uranium with about the same utilization as light water reactors. The breed-and-burn process that occurs within the 600 MWe reactor makes several times more efficient use of uranium resources, though the identification of large uranium resources makes this a relatively unimportant issue. The ultimate 1000 MWe Natrium reactor should make about 33 times more electrical energy per ton of mined uranium than present day light water reactors without the need for reprocessing.
The Natrium Demonstration Plant will prove out the systems and operations for the first generation of 345 MWe plants as well as qualifying many components for the larger breed-and-burn plants that follow. The plant will be started and initially checked out with the type of “sodium wetted” fuel that has been used before, including at INL. A transition to new higher performance fuel will then be made to achieve full commercial operations. The Natrium Demo is based on decades of sodium reactor operations and on a decade of focused development sponsored at national labs, universities, and companies.
The public-private partnership, or cooperative agreement, for the design and construction of a Natrium Demonstration Project was approved by DOE. The agreement calls for startup in seven years from signing. This aggressive schedule assumes funding is provided on the “S-curve” needed for on-time completion.
