Nuclear fusion is a nuclear reaction in which two nuclei of light atoms join together to form a heavier nucleus. The most practical element in the periodic table is hydrogen and its isotopes, deuterium, and tritium.
Nuclear fusion reactions can emit or absorb energy. If the nuclei to be fused have less mass than iron, energy is released. Conversely, if the merging atomic nuclei are heavier than iron, the nuclear reaction absorbs energy.
The emitted energy is so great that matter can become a plasma state.
It has not yet been possible to build any fusion power plants capable of producing electrical energy by now. However, several projects are currently being worked on - such as the ITER project in the south of France - to generate clean energy through fusion energy.
Example of Nuclear Fusion in the Sun
The prominent example of nuclear fusion is stars, including the Sun. The solar light and heat that we perceive result from the fusion of hydrogen nuclei due to the high pressure and temperature inside.
The energy released by the Sun reaches the Earth in electromagnetic radiation.
Inside the Sun, the temperature is close to 15 million degrees Celsius.
What Is Needed to Obtain a Nuclear Fusion Reaction?
The following requirements must be accomplished to carry out nuclear fusion reactions:
Achieve a very high temperature to separate the electrons from the nucleus and bring it closer to another, overcoming the electrostatic repulsion forces. The gaseous mass composed of free electrons and highly ionized atoms is plasma.
Confinement is necessary to keep the hot plasma at an elevated temperature for a minimum amount of time.
The plasma density must be sufficient so that the nuclei are close to each other and can generate nuclear fusion reactions.
Confinement for Nuclear Fusion
Conventional confinements used in nuclear fission reactors are impossible due to the high plasma temperatures they must withstand. For this reason, two important confinement methods have been developed:
Nuclear fusion by inertial confinement (FCI): It creates a medium so dense that the particles have almost no chance of escaping without colliding with each other.
Nuclear fusion by magnetic confinement (FCM): The electrically charged particles of the hot plasma are trapped in a reduced space by the action of a magnetic field. The most developed device has a toroidal shape and is called Tokamak.
How Does Nuclear Fusion Work? Nuclear Fusion Reactions
The atomic elements normally used in nuclear fusion reactions are Hydrogen and its isotopes: Deuterium (D) and Tritium (T). The most important fusion reactions are:
D + T --> 4He + n + 17.6 MeV
By fusing a Deuterium nucleus with a Tritium nucleus, a Helium nucleus formed by two neutrons and two protons is obtained, releasing one neutron and 17.6 MeV of energy.
D + D --> 3He + n + 3.2 MeV
By fusing two Deuterium nuclei, a Helium nucleus consisting of one neutron and two protons are obtained, releasing one neutron and 3.2 MeV of energy.
D + D --> T + p + 4.03 MeV
By fusing two Deuterium nuclei, a Tritium nucleus, a proton, and 4.03 MeV of energy are obtained.
For these reactions to occur, the nuclei must be supplied with the necessary kinetic energy to bring the nuclei to be fused, thus overcoming the electrostatic repulsion of nuclear forces. It requires heating the gas to very high temperatures, such as those supposed to occur in the center of stars.
It is essential to confine said plasma at a high enough temperature and density and for just enough time to allow enough nuclear fusion reactions to occur. Meanwhile, it prevents particles from escaping for a net gain of energy.
This energy gain depends on the energy needed to heat and confine the plasma being less than the energy released by nuclear fusion reactions. In principle, 335 MJ can be obtained for every milligram of deuterium-tritium.
What Is the Fuel of Nuclear Fusion?
For nuclear fusion reactions, we need light nuclei. As a result, Deuterium and Tritium are used, two isotopes of hydrogen (the lightest element in the periodic table).
Deuterium is a stable isotope of hydrogen, consisting of one proton and one neutron. Its abundance in water is one atom for every 6,500 hydrogen atoms. It means that there is a concentration of 34 grams of deuterium in seawater per cubic meter of water in seawater.
The energy content of deuterium is so high that the energy obtained from deuterium in one liter of seawater is equivalent to the energy obtained from 250 liters of oil.
The other element used in nuclear fusion, tritium, is the unstable or radioactive isotope of the hydrogen atom. It is composed of one proton and two neutrons and decays by beta emission relatively quickly.
Although tritium is rare in nature, it can be generated by neutron capture reactions with lithium isotopes. Lithium is an abundant material in the earth's crust and seawater.
Nuclear Fusion Reactor: Research Project
Magnetic confinement's most advanced fusion project is the ITER (International Thermonuclear Experimental Reactor). It is a prototype based on the Tokamak reactor concept, in which ignition is expected to be achieved.
Fusion researchers obtained excellent results in the Joint European Torus (JET) in Culham Centre for Fusion Energy. In 1990, they decided to continue the fusion program with a larger facility. Besides the reactor, its auxiliary systems could be tested without generating electricity. The European Union, Canada, USA, Japan, and Russia participate.
The objective is to determine the engineering challenges and economic feasibility of nuclear fusion by magnetic confinement to generate electricity.
Electrical energy will not be produced in the ITER machine, and solutions to the problems that need to be solved to make future nuclear fusion reactors viable will be tested.