A Dream that Began 70 years ago with ‘Nuclear-Powered Aircraft’… Safe ‘Liquid Salt’ Reactor
Nowadays, interest in nuclear power generation is increasing around the world. As reducing carbon emissions becomes an urgent task due to the climate crisis, the need for nuclear power is highlighted. However, it is also true that it is worrisome considering the risk of radioactive accidents.
What if we create a nuclear reactor that eliminates the possibility of fatal accidents? Following China, the United States is said to have begun construction of a molten salt reactor, one of the fourth generation nuclear reactors. Let’s take a look at the Molten Salt Reactor (MRS), a technology that originated from the ‘nuclear-powered aircraft’ idea about 70 years ago.
Let me start with an old story for a moment. How powerful would it be if a fighter jet was developed that could fly in the sky for weeks on end? During the Cold War, there was actually an attempt to develop such an aircraft. This is the ‘nuclear-powered aircraft’ that the United States was developing.
Humanity’s first nuclear-powered submarine, the Nautilus (launched in 1954), was equipped with a pressurized water-cooled water reactor. This pressurized water reactor method later became the standard for nuclear power generation around the world. But to fit in an airplane, a new type of nuclear reactor was needed that was much smaller and lighter. This is why the United States is developing a ‘molten salt reactor’ that uses liquid fuel instead of solid and uses molten salt (salt that melts at high temperature to become liquid) as a coolant instead of water.
In 1954, the U.S. Oak Ridge National Laboratory succeeded in developing a small nuclear reactor using molten salt for the first time in the world.U.S. Air Force was truly willing to develop a nuclear-powered aircraft. This can be seen from the fact that from 1955 to 1957, dozens of test flights were carried out carrying a small nuclear reactor on the ‘NB-36H’ bomber. This bomber, with its radiation markings on its tail, was not actually powered by nuclear energy. Instead, we confirmed that the flight system and crew are safe even when carrying a nuclear reactor (radiation is shielded with lead and rubber).
However, this nuclear-powered aircraft plan was canceled by President Kennedy in 1961 after controversy. The reason was, “Although we invested about 1 billion dollars, it is unlikely that we will develop a military useful aircraft in the near future.” After that, U.S. molten salt reactor experiments continued for some time. Oak Ridge National Laboratory also operated an experimental molten salt reactor from 1965 to 1969. That was it. The reactor was shut down in December 1969, and the U.S. government halted the project.
And now, decades later, molten salt reactors, once a forgotten technology, are coming back to life. China is the most advanced. China, which has been building a molten salt reactor in the Gobi Desert since 2018, finally approved test operation of the reactor last June. China’s Shanghai Applied Physics Laboratory was in charge of test operation.
The United States, a technology aid provider, also jumped in again. However, the private sector, not the government, is leading development. On the 12th of this month, the U.S. Nuclear Regulatory Commission approved the construction of a pilot reactor by Kairos Power, a molten salt reactor startup. This $100 million project, to be built in Tennessee, USA, is scheduled to be completed in 2026. Kairos Power explains, “This is the first time in 50 years that the United States has approved the construction of a nuclear reactor that is not water-cooled.
In addition to Kairos Power, startups that have jumped into the development of molten salt reactors include those in the United States. There are about 25 locations in Europe. Terra Power, founded by Microsoft (MS) founder Bill Gates, is one of them .dozens. Over the years, the nuclear power market has been dominated by water-cooled types (light water reactors, heavy water reactors). But why are many countries and companies now paying attention to the liquid salt cooling method (molten salt reactor) again?
Due to the distinct advantages of molten salt reactors. This means that there is almost no risk of a fatal accident.
The most dangerous thing among nuclear power plant accidentsCore meltdown. This means that because the coolant is not supplied properly, the internal temperature rises rapidly and the nuclear fuel rods melt. Major nuclear power plant accidents in history, such as the 1979 U.S. Three Mile Island nuclear power plant accident, the 1986 Soviet Chernobyl nuclear power plant accident, and the 2011 Fukushima Daiichi nuclear power plant accident, were all caused by core meltdowns.
Uranium reactors Even if the nuclear reaction is stopped, the remaining radioactive elements generate decay heat. So, you have to keep supplying coolant for several days to cool down the heat. During the Great East Japan Earthquake in 2011, the cooling water injection pumps at Fukushima Daiichi Nuclear Power Plant were shut down due to a power outage. Coolant circulation stopped, and the coolant inside the reactor evaporated, exposing the nuclear fuel rods to the air. The temperature of the fuel rod rises to 1,200 degrees, causing a core meltdown, causing the protective wall to melt and even causing a hydrogen explosion.
What if we use a coolant that has a very high boiling point and will not evaporate? Then there is no need to replenish the coolant. Even if the power is cut off due to an accident, the coolant will still remain and cool down, making it much safer. Molten salt has this advantage. The boiling point of molten salt is very high, over 1500 degrees even at atmospheric pressure. What if an accident occurs and the electricity supply to the molten salt reactor is cut off? If you just leave it alone, it will cool down on its own. Per Peterson, professor of nuclear engineering at Berkeley University, explains: “Molten salts are inherently attractive because they don’t boil over. This is why it has emerged as one of the most important technologies in the field of nuclear energy.”
It is also important to note that ‘nuclear fuel assemblies’, which are large bundles of uranium fuel rods, are not used. This is a major feature of molten salt reactors. Usually, liquid nuclear fuel is used. In the case of Kairos Power, small solid fuel the size of a ping-pong ball is used.
There are many advantages to not using nuclear fuel assemblies. First of all, the size of the reactor can be reduced (the nuclear fuel assembly is up to 4m in length). Also, there is no need to stop driving to change fuel every 18 months like now. Just just keep running it and refill fuel. Perhaps unmanned driving, such as adding fuel online, will be possible. Also, less fuel rod waste is generated.
Because molten salt is resistant to high temperatures, the operating temperature of the nuclear reactor can be raised higher than before. Increasing the operating temperature increases thermal efficiency (the amount of useful energy produced relative to the heat input to the system). The thermal efficiency of existing water-cooled reactors is about 32%, but that of molten salt reactors reaches 45%.
In summary, molten salt reactors are safer, more convenient, and more efficient. However, to reach commercialization, it must undergo verification, and there is a long way to go. In particular, the biggest obstacle is this. Corrosion.
Salt can cause corrosion to many metals. If the reactor vessel or pipes corrode, radioactive materials may leak, so this is not a big deal. For this reason, developing materials that are resistant to corrosion is an important task.
What is the status of MSR development in Korea? You might be wondering about this. How far has our country come in this new nuclear reactor technology? So, I had a phone interview with Lee Dong-hyeong, director of the Korea Atomic Energy Research Institute’s Molten Salt Reactor Source Technology Development Project. -Korea Atomic Energy Research Institute has also been researching molten salt reactors for several years, right? “Yes.
However, it was a little late because it only became an official national research and development project of the government in April of this year. China began development about 10 years ago. In the United States and Europe, not only government support but also private capital has been injected enormously since 2018 and 2019. Still, our researchers are starting with a certain degree of design technology and molten salt-related technology. Now, if we work harder, I think we can catch up.”– Looking at China and the United States, there is a long way to go before commercialization, and they are just about to start pilot operations. It will still take some time for our country to reach the pilot operation stage, right?“
Our project is to develop the original technology by 2026. In order to verify it later, it will be necessary to make a plan again and invest financial resources. However, what is encouraging is that rather than being developed solely by researchers, private companies such as Hyundai Engineering & Construction, Samsung Heavy Industries, HD Korea Shipbuilding & Marine Engineering, and Century came in to work together. We are developing.
The government’s policy is not to stop at research and development but to hasten development for commercial purposes.”-Has the use of the molten salt reactor to be developed been decided? Is it for ship propulsion or general inland electricity production? “Currently, the priority is to target offshore plants and ship propulsion I am doing it.
Many efforts to apply molten salt reactors to the ocean have already been attempted in the United States, China, and Denmark, so we set our sights there as well. However, whether it is an offshore plant or ship propulsion, ultimately all generate electricity. Once it is proven at sea, there will be no problem bringing it inland.”-Why are shipbuilders particularly interested in molten salt reactors?“
Shipbuilding companies have been developing ammonia, hydrogen, and methanol as eco-friendly energy, but now nuclear power has emerged as another option. If the fuel tank is large, it is difficult to load a lot of cargo. In that respect, nuclear power has merit.”
-A big advantage of molten salt reactors is that they can greatly reduce the generation of nuclear waste?
“Recently, technology has been developed with the goal of ensuring that all nuclear reactors have very long nuclear fuel replacement cycles. It’s in progress. Instead of replacing it every 18 months like it is now, the goal is to not emit fuel for more than 12 to 20 years. It reduces the amount of spent nuclear fuel generated.There is also a technology that our research institute is developing together with the private sector.
A lot of plutonium accumulates in spent nuclear fuel. We are developing a nuclear reactor that can burn it without reprocessing it. That way, we can further reduce the amount of waste generated.”-To what extent has the technology been developed? “Conceptually, it has been around for a long time, that is, 60 years ago. It was a technology that existed. Of course, several methods are needed for design, but the most important thing is verification.”
–They say the reason it is difficult to make a molten salt reactor is corrosion. Are you still looking for a solution? “Not only we, but research reactor development companies in each country are investing a lot of money and manpower to develop technology to protect them by coating them with corrosion-resistant materials. there is. Now, those solutions are being announced one by one. Of course, the core content is not disclosed. That part is one of the biggest topics in nuclear power.”-Preventing corrosion is not a difficult technology. I thought it was a much more important issue in the industry than I thought.
“Because safety must be guaranteed. Also, in the case of ships, the lifespan is 30 years, and since it is better not to replace them mid-term if possible, in terms of waste and all other aspects, we are making a lot of efforts to protect them safely.” By. Deep Dive These days, there is a lot of interest in small module reactors (SMRs). SMR has even become a theme in the domestic stock market.
The molten salt reactor (MSR) explained today also belongs to one of these types of SMRs. This is an interesting topic because it has many differences from the existing nuclear reactors we know. To summarize the main content-Following China’s start of test operation of a molten salt reactor in June of this year, the United States also approved the construction of a pilot reactor by the startup Kairos Power. The race to develop next-generation nuclear reactors using liquid salt, or molten salt, is in full swing. -Molten salt reactor is a technology that already came out in the 1950s.
It was initially developed to be used as a power source for ‘nuclear-powered aircraft’. After this plan was canceled, momentum was lost and the project was discontinued.-The reason molten salt reactors are attracting attention again after decades is because of their excellent safety. It also has the advantage of being miniaturized and unmanned and has high thermal efficiency. -Korea also selected this as a national development project starting this year and began developing source technology. In particular, we plan to develop eco-friendly ships and offshore plants.