Why No Commercially Viable Nuclear Fusion Reactors?

The nuclear reactors use the heat produced during a nuclear reaction. The nuclear reaction can be either Nuclear Fission or Nuclear Fusion; but so far, nuclear fusion reactors are only under experimental stages. Once proved viable, the nuclear fusion reactors may be of high advantage over the current nuclear fission reactors.

Why no commercially viable fusion reactor?

In nuclear fission, we break the heavy nuclei into smaller nuclei and get energy as side-product; in Nuclear Fusion, we combine light nuclei such as Hydrogen to heavier nuclei such as Helium and get energy as side-product.  The cited advantages of nuclear fusion include:

• Availability of abundant Hydrogen (which is used as fusion fuel), that can be extracted from water.
• Possibility of generation of low nuclear waste.
• Possibility of low nuclear radiation leaks.

Despite of these advantages, researchers are yet to create commercially viable nuclear fusion reactions.  The reason is as follows:

Unlike fission, Nuclear Fusion needs energy to overcome the barrier of electrostatic forces before fusion can occur. The two naked nuclei repel one another because of the repulsive electrostatic force between their positively charged protons. Bringing them close enough is a challenge. Thereafter, if the two nuclei can be brought close enough together; the attractive nuclear force, which is stronger at close distances is what will be helpful for fusion of the nuclei. Therefore, the prerequisite for fusion is that the nuclei must have enough kinetic energy that they can approach each other despite the electrostatic repulsion. This kinetic energy has to be provided for consumption in the fusion reactor to produce subsequent nuclear fusion energy. For this, Fusion needs high temperature and high pressure.

• The high temperature gives the hydrogen atoms enough energy to overcome the electrostatic repulsion. Fusion requires temperatures about 100 million Kelvin (around six times hotter than the sun’s core). At these temperatures, hydrogen is a plasma, not a gas.
• The high pressure is needed to squeeze the hydrogen atoms together. They must be within 1×10-15 meters of each other to fuse.

Thus, in current methods, the consumption of energy is high but production is subsequently low. The current methods cannot produce as much useful energy as the nuclear fusion would consume, i.e. the break-even point. Sustaining reactions that produce enough energy to make them a commercially viable power source is even further away.