In this blog post, we’ll take a natural look at the principles, advantages, limitations, and future potential of nuclear fusion power.
Currently, most of the energy consumed worldwide relies on fossil fuels such as coal and oil. However, the use of these fossil fuels has caused various problems. Climate change and extreme weather events caused by greenhouse gas emissions, international conflicts stemming from the uneven distribution of resource reserves, and energy price volatility have further heightened the need for new energy sources. In addition, the international community is promoting various agreements and policies to reduce greenhouse gas emissions, and as a result, many countries are striving to develop next-generation energy sources to replace fossil fuels. Among these alternatives, nuclear fusion power is gaining attention as a future energy technology, and active research is underway. Since the Sun also generates immense amounts of energy through nuclear fusion reactions, nuclear fusion power can be described as a technology that replicates the energy-generation principles occurring on the Sun here on Earth.
The primary fuels for nuclear fusion power are deuterium, tritium, and helium-3. While ordinary hydrogen consists of one proton, deuterium is a hydrogen isotope with one additional neutron and is denoted by the symbol D. Tritium is a hydrogen isotope with two additional neutrons and is denoted by the symbol T. Helium-3, meanwhile, is a helium isotope with one fewer neutron than ordinary helium.
Although there are various types of nuclear fusion reactions, the fusion power generation currently under research is broadly classified into three categories. These are generally referred to as first-generation, second-generation, and third-generation fusion reactions; the first generation involves the reaction between deuterium and tritium, the second generation involves the reaction between deuterium and deuterium, and the third generation involves the reaction between deuterium and helium-3. This classification is based on the characteristics of the fusion reactions and the conditions required for them. When comparing reaction characteristics, first-generation reactions using deuterium and tritium occur more readily at relatively lower temperatures than other methods, making them the subject of the most active research today.
In first-generation nuclear fusion reactions, deuterium and tritium combine to produce helium and a neutron while releasing enormous amounts of energy. Most of the energy produced takes the form of kinetic energy from the neutrons and helium; the heat generated during the process of slowing down the neutrons is used to create steam, which drives a turbine to generate electricity. Deuterium and tritium, the fusion fuels, are expected to have a relatively stable supply. Since deuterium occurs naturally in water—including seawater—it can be extracted; however, tritium is a radioactive isotope and must be produced continuously. To achieve this, a breeding process is used in which neutrons generated during the fusion process react with lithium to produce tritium. Lithium is also known to be a relatively abundant resource, making the long-term availability of fuel highly likely.
The ultimate goal of fusion research is third-generation fusion reactions. First- and second-generation reactions produce neutrons, which are used in conventional power generation methods to generate heat and steam to drive turbines. The efficiency of this type of power generation is generally around 30–40%. In contrast, in third-generation reactions, deuterium and helium-3 react to produce protons and helium. Since the protons produced in this process are charged, they can potentially be converted directly into electrical energy; therefore, theoretically, a higher energy efficiency can be expected. However, securing helium-3 fuel and overcoming the associated technical challenges remain issues that need to be addressed.
As such, nuclear fusion power generation offers the advantages of an abundant and, in the long term, highly stable fuel supply, as well as the fact that it does not directly emit carbon dioxide during the power generation process. Furthermore, unlike conventional fission power generation, it does not rely on a chain fission reaction, which is expected to reduce the risk of accidents. However, due to various technical limitations, it has not yet reached the commercialization stage. The greatest challenge is maintaining a stable fusion reaction. The fusion reaction between deuterium and tritium requires an ultra-high-temperature environment of approximately 100 million °C or higher, and no solid material exists that can withstand such temperatures. Therefore, research is currently focused on using powerful magnetic fields to control the ultra-high-temperature plasma so that it does not come into contact with the reactor walls. Additionally, technologies for maintaining plasma stably over long periods and for continuously producing more energy than is input into the fusion reaction are also critical challenges that must be overcome for commercialization. Recently, research to solve these technical problems has been actively underway at various research institutions around the world, and it is expected that if fusion power generation is commercialized in the future, it will mark a major turning point in solving humanity’s energy problems.
