The Difference Between Nuclear Fusion and Fission Power

Fusion power generation utilizes the energy released when atomic nuclei fuse together. This principle is based on Albert Einstein's mass-energy equivalence formula:
E=mc² (E: Energy, m: Mass, c: Speed of light)

To explain in detail: atomic nuclei are found in all atoms, and their mass varies by element. For example, a standard hydrogen atom has an atomic mass of approximately 1, carbon is 12, and oxygen is 16. However, isotopes such as deuterium and tritium (types of hydrogen) have atomic masses of 2 and 3, respectively.

On the other hand, some heavy nuclei, such as uranium-235 and uranium-238, weigh more than 200 times as much as hydrogen. Plutonium is also 239, which is a famous element related to "nuclear technology". Some artificially created elements are heavier, for example, the atomic weight of nihonium successfully synthesized by RIKEN is 286.

When light atomic nuclei fuse to form a heavier nucleus--a process called "nuclear fusion"--energy is released. Fusion power typically employs a reaction between deuterium and tritium (D-T reaction) to produce helium. This is the same process that powers the sun. During this reaction, the mass of the resulting nucleus is slightly less than the combined mass of the original nuclei. This lost mass is converted into enormous energy, which can be used to generate electricity.

Specifically, the heat generated by the fusion reaction is used to produce high-temperature steam, which drives a turbine connected to a generator.

Key Advantages:

1. Carbon-Free: Like thermal power, it generates massive energy but without CO₂ emissions.
2. Abundant Resources: Deuterium can be extracted from seawater, making fuel sources virtually inexhaustible globally.
3. Inherent Safety: Unlike fission, there is no risk of a runaway chain reaction. If the reactor is compromised, the fusion reaction stops automatically.

Disadvantage: The neutrons produced during the reaction activate the reactor walls, creating low-level radioactive waste that requires proper management.

So, what is nuclear power generation that also uses atomic nuclei? Unlike the nuclear fusion introduced above, nuclear power generation uses the energy generated by "fission."
For example, the nucleus of uranium-235 becomes unstable when exposed to neutrons and splits into multiple lighter elements.

In this time, the mass of all the elements after division is lighter than that of the original uranium-235, so the difference comes out as energy. It is the same as thermal power generation that the energy that comes out generates steam to turn the turbine.

The problem is that uranium-235 has radioactivity. If the reaction rate cannot be controlled well, the reactor may explode, and uranium-235 and plutonium-239 will be scattered around. This was the accident that occurred at the Chernobyl nuclear power plant and the Fukushima Daiichi nuclear power plant.
In addition, even if an explosion does not occur, the elements after division may also have radioactivity, so how to dispose of the remaining nuclear waste is also a problem.

So how far has fusion power been developed? As a matter of fact, at present, there is still no commercial power plant.
Since nuclear fusion is also a phenomenon occurring in the sun, it is necessary to cause a reaction by hitting deuterium, which is a fuel, in an ultra-high temperature state. Moreover, to keep deuterium in an ultra-high temperature state, the inside of the fusion reactor must be evacuated. This is because the presence of other gases can get in the way. And it is necessary to confine it with a strong magnetic field so that it does not diffuse from the reactor.
Another method is "laser fusion," in which deuterium is contained and nuclear fusion is performed by shining a high-power laser from around 360 degrees.

However, enormous energy is required to achieve all the conditions. We are trying to perform nuclear fusion to extract energy, but it takes a huge amount of energy to perform nuclear fusion.
In the research, no matter how much energy you put in, it doesn't matter if you can confirm the fusion reaction. However, when it comes to power generation, it is meaningless unless we can extract more energy than we put in. For example, the unit can be kW, MW, or GW, so if you put in 1 (ex. GW), you need to be able to take out 1.1 (GW). It cannot be used for commercial power generation if 1 (GW) is input and only 0.9 (GW) can be taken out.

So how far have we been now? In 1968, humankind first succeeded in artificially generating a fusion reaction in a magnetic field-based fusion reactor developed by the former Soviet Union. Naturally, at this time, the amount of energy input was many orders of magnitude higher than the amount of energy that could be extracted.
In 1998, it was the fusion experimental reactor JT-60 owned by the Japan Atomic Energy Research Institute that produced the experimental results that seemed to exceed the energy extracted for the first time in the world. Still, it was not enough to generate electricity.

At present, research on fusion power generation is progressing so that the value of Q will be about 5 to 10. Q can be calculated by the following formula.
Q = Output energy ÷ Input energy

Well what kind of structure does a fusion reactor have? There are two types, "magnetic confinement fusion reactor (MCFR)" and "inertial confinement fusion reactor". Among the MCFR, the "tokamak fusion reactor (TFR)", which has the longest research history, is the most advanced and adopted by ITER. JT-60 is also this type. The "laser fusion" introduced earlier is an "inertial confinement fusion reactor" type.

In the TFR, the inside of the fusion reactor is evacuated, and the fuel heated to 100 million degrees or more (the target temperature is 120 million degrees or more) and turned into plasma is put into it. Plasma is made by stripping all electrons from an atom and leaving only the nucleus.
Then, it is confined in a narrow area with a strong magnetic field so that the temperature of the fuel plasma can be kept at an ultra-high temperature. Otherwise, the plasma will hit the walls of the fusion reactor, lose energy and cool.

This magnetic field is generated by the current flowing in the toroidal direction. This current is called plasma current. And the larger the plasma current, the higher the plasma performance. However, the strength of the magnetic field generated by this plasma current is 4.0T (Tesla) for JT-60 and 5.2T for ITER. The value of plasma current reaches 15 million A.

A superconducting material is indispensable for the stable flow of such a large current. If there is resistance, heat will be generated by that amount, so extra power will be required. Nb3Sn superconducting wire is used in ITER, but it is not a high-temperature superconductor. Therefore, some power is required for cooling this wire.

Plasma Diagnostics and Power Supplies
To maintain stable fusion, the state of the confined plasma must be precisely measured. One common method is using a Langmuir probe, where microelectrodes are inserted into the plasma to measure current-voltage characteristics. This requires high-speed, high-precision voltage application.