What is Fusion?
Fusion is the reaction that generates heavy atomic nuclei and releases massive amounts of energy by fusing two light atomic nuclei.
For example, in the case of the D-T reaction between the hydrogen isotopes deuterium (D) and tritium (T), the energy obtained from 1 gram of fuel (D and T) is equal to the energy obtained by burning 8 tons of oil.
Fusion energy is attracting attention as “dream energy” because it has the following four characteristics.
(1) Carbon neutral
No greenhouse gases such as carbon dioxide are produced by fusion reactions.
Furthermore, because they do not generate sulfur dioxide or nitrogen oxides, which cause acid rain, they are extremely environmentally friendly energy sources.
(2) Inherent safety
Fusion is extremely difficult to generate a reaction. If the reaction conditions are no longer satisfied for some reason, the fusion reaction will automatically stop.
In other words, there is no risk of criticality accident by nature of fusion.
(3) Stable supply
Unlike renewable energies such as solar power and wind power, fusion power generation is not affected by external environmental factors such as weather. Therefore, if realized, it will be possible to stably supply large amounts of power.
(4) Environmental integrity
All radioactive waste produced by fusion reactions is classified as “low-level radioactive waste” and can be disposed of using existing technology.
Furthermore, the “advanced-fuel fusion,” which we aim for, is an extremely environmentally friendly energy source that generates almost no even low-level radioactive waste.
What is “Advanced-Fuel” Fusion?
Advanced-fuel fusion refers to fusion reactions that include no radioactive substance tritium in the fuel and generate almost no neutrons (i.e., little radioactive waste).
For example, it includes the d-3He reaction and the p-11B reaction. Here,
- D : Deuterium (isotope of hydrogen H)
- 3He : Helium 3 (isotope of helium)
- p : proton (nucleus of hydrogen H)
- 11B : Boron 11 (isotope of boron).
The D-T reaction between the hydrogen isotopes deuterium (D) and tritium (T) is generally well known, but most of the energy released in this reaction is generated as high-speed neutrons.
In order to realize fusion energy through the D-T reaction, it is necessary to solve the challengess caused by tritium in the fuel and the generated neutrons (described later). For this reason, we are working to realize advanced-fuel fusion power generation through the p-11B reaction, which does not, in principle, cause these problems.
Challenges of the D-T Fusion Reactor
Challenges caused by the generated neutrons
Radioactivation of materials
When the neutrons generated by the fusion reactions collide surrounding equipment, the materials become radioactivated (changed into radioactive substances). In order to suppress this, it is possible to keep the radioactivity level low by using materials that do not easily become radioactive. However, the current situation is that the issue of generating large amounts of radioactive waste, even if it is at a low level, has not been sufficiently discussed.
Embrittlement of metal materials
Metals have the property of becoming brittle when irradiated with neutrons. The more neutrons are irradiated, the more brittle the metal materials used for the fusion reactor walls become, so materials such as the reactor walls need to be replaced periodically, which can be costly.
Challenges caused by using tritium as fuel
Fuel supply
Of the hydrogen isotopes that exist in nature, light hydrogen (H) accounts for 99.985%, deuterium (D) accounts for 0.015%, and tritium (T) is almost absent. Therefore, in a D-T fusion reactor, it is necessary to generate (breed) tritium by colliding the neutrons obtained from the reaction with the lithium contained in the “blanket” installed to surround the fusion reactor.
On the other hand, as explained later, tritium is extremely difficult to handle, and it is necessary to maintain an appropriate amount to sustain the fusion reaction.
Furthermore, the appropriate breeding rate of tritium in a D-T fusion reactor cannot be experimentally verified unless the reactor is a reactor that generates a D-T fusion reaction, which poses the “chicken-and-egg” problem.
Difficult to handle
Tritium is a radioactive substance and is one of the most important factors when considering the safety of D-T fusion reactors. Although it is a radioactive substance, the energy of the beta rays (a type of radiation) emitted by tritium is extremely small, and the effects on the human body from external exposure to radiation can be ignored.
On the other hand, the effects on the human body when taken into the body (internal exposure) cannot be ignored. [1] In a D-T fusion reactor, because tritium is widely distributed throughout the facility, it is necessary to confine it within the facility and process it reliably. [2]
Because of these challenges, further research and development of materials for reactors and peripheral equipment is required for commercial use of fusion energy from D-T reactions.
Fusion Energy that We Aim For
The fusion reactions that we are aiming for use hydrogen (H or p) and boron (11B) as fuel, and extracts energy from the product helium nucleus (alpha rays), as shown in the diagram below.
Therefore, the p-11B reaction that we are aiming for does not have the various problems caused by tritium and neutrons, so it can be used as a fusion reactor that is significantly safer and more economical, and has high social acceptance. This reaction has the general characteristics of fusion mentioned above: (1) carbon neutrality, (2) inherent safety, (3) stable supply, and the characteristics of advanced-fuel fusion: (4) almost no radioactive waste generated. In addition to this, it also has the following features:
Abundant Fuel
The fuel for the p-11B reaction is hydrogen and boron-11. Hydrogen can be extracted from seawater, so it can be produced abundantly.
The recoverable reserves of boron are estimated at 1.1 billion tons [3]. 80% of naturally occurring boron is boron-11. If we calculate the reserves-to-production ratio based on the amount of recoverable reserves and the current production volume [4], it is predicted that the resource will not be exhausted for about 200 years.
Furthermore, this “200 years of reserves-to-production ratio” is calculated based on the amount of boron that can be mined using current technology and prices (that is, by producing boron from boron minerals).
On the other hand, boron exists in several milligrams per liter of seawater, and the technology to recover boron from seawater has already been established. When the p-11B reaction is realized in the future, it is expected that a much larger amount of boron will be required than at present, but this can be met by recovering it from seawater, so the fuel is almost inexhaustible.
Suitable for smart cities and compact cities
The fusion method we are aiming for generates almost no radioactive materials and can realize an extremely compact fusion reactor, which can be installed as an “urban power plant” near large cities. Furthermore, since the power required for start-up can be supplied directly from the grid, it can be used as an “off-grid power plant” that can be installed directly at a data center or remote island.
Therefore, it is possible to reduce problems such as power loss due to power transmission lines and power outages due to disconnection of power lines.
In this way, the fusion energy produced by the p-11B reaction can truly be called “dream energy” that has the potential to enrich our lives while protecting the global environment.
Therefore, we are working hard on research and development with the aim of realizing this “dream energy” as soon as possible.
References
[1] Masanori Hara, Satoshi Akamaru, Masato Nakayama, “Research frontier of tritium for fusion reactor – toward the DEMO reactor (11); Safety control of tritium in work area,” Journal of Nuclear Science and Technology Vol.61, No.7 (2019),
[2] Yasunori Iwai, Yuki Edao, Kanetsugu Isobe, “Research frontier of tritium for fusion reactor-toward the DEMO reactor (9); Tritium safety confinement,” Journal of Nuclear Science and Technology Vol.61, No.5 (2019),
[3] U.S. Geological Survey, Mineral Commodity Summaries, January 2018,
[4] Boron market size and share analysis – growth trends and forecasts (2024-2029), Mordor Intelligence,