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On June 10, 2024, TerraPower, a nuclear energy company invested by Microsoft founder Bill Gates, announced that its $4 billion Next-generation (also known as the "fourth generation") nuclear power plant Natrium reactor broke ground in Kemmerer, Wyoming. The project is a 345MW sodium-cooled fast reactor equipped with a molten salt energy storage system, which can increase the output power to 500MW when the power grid needs it. It is expected to be put into operation in 2030.

Bill Gates invested in nuclear energy very early. TerraPower, founded in 2006, cooperated with Pacific Power Company under Buffett's Berkshire Hathaway in 2021 to continue to develop the "fourth generation" sodium-cooled fast neutron reactor (SFR), and hopes to achieve the application of 5 new nuclear power plants by 2035. The significant improvement in energy efficiency has greatly promoted production, lifestyle and civilization.

Dangerous sodium

Unlike the third-generation nuclear power "light water reactor" which uses water as a moderator and heat transfer medium, the so-called fourth-generation nuclear power Natrium uses liquid metal sodium as a working fluid. The common pressurized water reactor (PWR) today can achieve heat exchange at 325°C without vaporization under 150 atmospheres. The boiling point of metallic sodium is 883°C, so the "nanocooler" can increase the operating temperature of the reactor to 550°C without pressurization. The thermal conductivity of metallic sodium is 50 times that of water. Considering the higher operating temperature mentioned above, the "Nuclear Regulatory Commission (NRC)" assesses that the heat exchange efficiency of liquid metallic sodium is 100 times that of water, and its working efficiency is much higher than that of the third-generation nuclear power.

"Light water reactors" (including boiling water reactors and pressurized water reactors) can only use uranium 235, which accounts for about 0.72% of natural uranium, and cannot use uranium 238, which accounts for 99.28% of natural uranium. Therefore, after the nuclear fuel rods are scrapped, the residual radiation of nuclear waste is still very high, and the products after the fission reaction also contain a large amount of heavy elements, such as actinides, which are difficult to use and have great radiation hazards. The treatment, storage and safety of nuclear waste have become a global problem.

The "fourth generation" fast neutron reactor can use uranium 238, which is extremely abundant in natural uranium, to avoid the huge waste of nuclear materials. In addition, in a fast neutron reactor, uranium 238 captures fast neutrons and undergoes two beta decays to form plutonium-239, which can be used as an energy source for "radioisotope thermoelectric generators" and can be used to drive spacecraft. This "killing two birds with one stone" feature is called "breeding" in nuclear physics, and fast neutron reactors are therefore also called "fast neutron breeder reactors."

Higher efficiency means greater profits. Who wouldn't want such a good thing? Fast neutron reactors are not a new concept. As early as 1951, the first nuclear power plant in human history, the Experimental Breeder Reactor No. 1 (EBR-1), used the fast neutron reactor principle. The coolant used at that time was liquid sodium-potassium alloy.

However, the theory is advanced but the application cannot keep up, the science is perfect but the technology is difficult to achieve. This is inevitable in the process of transforming pure science into practical technology. It takes decades or even generations for the application and technology to mature. Early liquid metal fast breeder reactors could not overcome the corrosive effect of liquid metal sodium on containers and pipes.

Metallic sodium is very active. It will oxidize violently and burn when exposed to air, and may even explode if it comes into contact with water. Therefore, in industrial use, sodium must be soaked in kerosene for storage.

Historically, most liquid metal fast breeder reactors have had bad endings: the "Manjusri" reactor built in Japan in 1986 had cracks in the cooling system in 1995, leaking 640 kg of sodium vapor and causing a fire. Since then, it has continued to malfunction, and the deputy director of the affairs department of the Dynamic Burning Group committed suicide by jumping off a building to apologize, but it was unable to save the situation and was eventually shut down in 2010. In 1976, the Superphénix built in France was once the world's largest breeder reactor, but it also experienced corrosion and leakage in the liquid nitrogen cooling system, and was finally closed in 1997 due to various problems.

At present, the only "sodium-cooled reactors" still in operation in the world are Russia's BN600 and BN800. The former Soviet Navy's technological leap forward in using "sodium-cooled reactors" on the Type 705 nuclear submarines led to frequent nuclear accidents: the K-64 and K-123 submarines both suffered major nuclear accidents due to sodium coolant pipeline failures. The United States, which has a more advanced technological level, is not much better. The SSN-575, which was put into use in 1957, is the only nuclear submarine of the US military that uses a "sodium-cooled reactor". It also had a superheater leakage accident, which led to the dismantling of the "sodium-cooled reactor" in 1958 and the conversion back to the more backward pressurized water reactor.

In response to the hazardousness of metallic sodium, the scientific and technological community has been working tirelessly for decades and has tried a variety of materials such as mercury, lead, tin, sodium-potassium alloy, lead-bismuth alloy, etc. For example, the European Commission invested 6.6 million euros between 2015 and 2019 to build three fast neutron reactor demonstration projects, evaluate the thermal-hydraulic simulation and experimental program research SESAME, and study the flow of metal fluids in pipelines and nuclear reactors and their impact on equipment, focusing on laying the foundation for the development of nano-cooling and lead-cooling technology paths.

Can be used in nuclear weapons

Even if the safety problem of metallic sodium is solved, there is still a nuclear weapons safety problem that must be solved. The currently popular third-generation nuclear power "light water reactor" cannot be used for nuclear weapons and is considered a model of "peaceful use of nuclear energy." However, the reaction product of the "fast neutron breeder reactor," plutonium-239, is a weapon-grade nuclear material. The second atomic bomb "Fat Man" that exploded in Nagasaki in 1945 was a plutonium bomb. This is also the reason why Russia insists on keeping the "sodium-cooled reactor" and North Korea building heavy water reactors. Both types of reactors can produce weapon-grade plutonium-239 for the manufacture of nuclear weapons.

Therefore, the International Atomic Energy Agency emphasizes that countries with fast breeder reactors must have clearer policies and monitoring measures. But historical experience tells us that "enhanced management" based on human weaknesses is the least reliable. In comparison, the following technical ideas are slightly more reliable: completely change the design of nuclear fuel rods so that they can be directly run to complete scrapping after a single filling, and cannot be safely removed in the middle under the pretext of "maintenance", so as to avoid the fission product plutonium being secretly refined and stolen. If someone illegally dismantles or steals it, they will be exposed to lethal nuclear radiation, so as to avoid the risk of nuclear terrorist attacks.

Projects with higher risks should be built in relatively desolate, isolated, and sparsely populated areas. In the event of an accident, the degree of harm, public opinion control, and compensation for victims are relatively low. Wyoming, where Bill Gates and Buffett invested in the "fourth-generation" sodium-cooled reactor, is located in the western United States and is the least populous state in the United States, which conforms to the above conventional experience.

The question is: Have all the technical problems of the liquid metal fast breeder reactor, which has been repeatedly tried and failed in the past few decades, been solved by Bill Gates' scientific research team? Are the nuclear technology safety and nuclear weapons safety solutions really reliably guaranteed? Will the technology and process really mature to reach 5 new nuclear power plants in 2035? This is of course Bill Gates's trade secret, and the outside world can only verify it with time.

Molten salt energy storage system

In addition to the topic of nuclear power, there is also a non-nuclear but related technology, namely the molten salt energy storage system of the Natrium reactor. It can store surplus energy during the peak of nuclear power generation and the valley of market energy consumption; and during the peak of market energy consumption, it does not need to overload the Natrium reactor, but can increase the power output by about 45% to 155MW, while meeting market demand and ensuring the smooth operation and safety of nuclear power plants and power transmission and transformation networks.

The molten salt energy storage system uses the surplus energy of nuclear power plants to melt safe and cheap inorganic salts such as sodium nitrate, potassium nitrate, and calcium nitrate in high-temperature lava storage tanks to store huge amounts of thermal energy. When it releases energy, the high-temperature molten salt passes through a heat exchanger to drive a steam generator to generate electricity. This energy storage method is called "thermal energy storage TES." This energy storage method can already make the rate of thermal energy loss very slow. A paper in the scientific journal "Journal of energy storage" pointed out that the storage tank using new technology uses an insulation layer of about 125cm thick, and the monthly energy loss is only 5%. TES can achieve energy storage for months or even across seasons.

Compared with lithium-ion batteries, which only lose 0.5%-1% of energy per month on average, the energy storage effect of molten salt energy storage systems is not as good and the energy loss is relatively large. However, its mineral salt is low-cost and safer, and does not have the huge environmental pollution risk of chemical energy storage such as lithium ion.

This type of molten salt energy storage system can be used not only in nuclear power plants, but also in solar power generation systems. In 2018, the first thermal solar power plant that can generate electricity 24 hours a day, Gemasolar, was born in Spain. The mirror matrix placed in the desert is not a solar panel, but a molten salt power tower that focuses and reflects sunlight to the center of the site. It stores a mixture of 60% sodium nitrate and 40% potassium nitrate. When there is no sunlight at night, it can still generate stable electricity for 15 hours through the heat release of molten salt. Its 19.9MW power can provide stable electricity for 27,500 households.

The molten salt energy storage thermal solar power plant not only solves the weakness of traditional solar panels that they cannot generate electricity when there is no sunlight, but also uses reflective mirrors instead of photovoltaic panels, which reduces the large amount of heavy metal pollution generated during the production of photovoltaic panels and the lasting impact of discarded photovoltaic panels on the environment.

Chile saw the success of Spain and launched the Alba Project in 2019, planning to convert all coal-fired plants in its desert area into molten salt solar power plants with an installed capacity of 560MW, and ultimately hopes to completely eliminate traditional fossil fuel power generation by 2040. This is not just for environmental protection purposes. For Chile, which lacks fossil energy, if it can achieve energy substitution with new structures and 24-hour stable solar energy, it can save a lot of precious foreign exchange originally used to import energy. If it can export electricity to neighboring Latin American countries, it can earn a lot of foreign exchange hard currency.

If Bill Gates' Natrium reactor + molten salt energy storage system can succeed, it will undoubtedly greatly improve the efficiency of nuclear power generation. As for Buffett, who has always been shrewd and calculating, he rarely makes mistakes. This "fourth generation nuclear power" may have a broad market prospect.

Another perspective is: asOpenAIBill Gates, the biggest investor behind the project and a graduate of science and engineering, realized early on that AI/AGI R&D consumes a huge amount of energy. The nuclear power in his hands, combined with the molten salt energy storage system with surplus energy, can not only ensure the safety of the entire system, but also reduce the energy consumption cost of AI/AGI (general artificial intelligence) R&D.

This point coincides with that of another original technology giant, Musk. Musk invested in SolarCity very early on, and it has been proven that this has a significant impact on boosting Tesla's stock price and brand value. More profoundly, Musk's description of the future development of his artificial intelligence brands xAI and Neuralink explicitly mentioned the energy consumption issue of AI/AGI research and development. The two world's richest people are truly of the same mind.

• (This article is only the author's personal opinion and does not represent the position of this newspaper)

Wu Xu

Editor: Chen Bin