What is Fusion?

Fusion is the energy source of the Universe, occurring in the core of the Sun and stars. Fusion is the process at the core of our Sun. What we see as light and feel as warmth is the result of a fusion reaction: hydrogen nuclei collide, fuse into heavier helium atoms and release tremendous amounts of energy in the process.

The gravitational forces at play in the Universe have created the perfect conditions for fusion. Over billions of years, these forces caused the hydrogen clouds of the early Universe to gather into massive stellar bodies. In the extreme density and temperature of their cores, fusion occurs.

How does fusion produce energy? Atoms never rest: the hotter they are, the faster they move. In the core of our Sun, temperatures reach 15,000,000° Celsius. Hydrogen atoms are in a constant state of agitation, colliding at very great speeds. The natural electrostatic repulsion that exists between the positive charges of their nuclei is overcome, and the atoms fuse.  The fusion of light hydrogen atoms (H-H) produces a heavier element, helium.

The mass of the resulting helium atom is not the exact sum of the two initial atoms, however—some mass has been lost and great amounts of energy have been gained. This is what Einstein's formula E=mc² describes: the tiny bit of lost mass (m), multiplied by the square of the speed of light (c²), results in a very large figure (E), which is the amount of energy created by a fusion reaction.

Every second, our Sun turns 600 million tons of hydrogen into helium, releasing an enormous amount of energy. But without the benefit of gravitational forces at work in our Universe, achieving fusion on Earth has required a different approach.

Twentieth-century fusion science has identified the most efficient fusion reaction to reproduce in the laboratory setting: the reaction between two hydrogen (H) isotopes deuterium (D) and tritium (T).  The D-T fusion reaction produces the highest energy gain at the 'lowest' temperatures. It requires nonetheless temperatures of 150,000,000° Celsius to take place—ten times higher than the H-H reaction occurring at the Sun's core.

At extreme temperatures, electrons are separated from nuclei and a gas becomes a plasma—a hot, electrically charged gas. In a star as

in a fusion device, plasmas provide the environment in which light elements can fuse and yield energy.

In ITER (International Thermonuclear Experimental Reactor), the fusion reaction will be achieved in a tokamak (above) device that uses magnetic fields to contain and control the hot plasma. The fusion between deuterium and tritium (D-T) will produce one helium nucleus, one neutron, and energy.

Nuclear fusion is one of the most promising options for generating large amounts of carbon-free energy in the future. International fusion research is following a roadmap to achieve power generation within 30 years.

Nuclear FissionAn atom's nucleus can be split apart. When this is done, a tremendous amount of energy is

released. The energy is both heat and light energy. Einstein said that a very small amount of matter contains a very LARGE amount of energy. This energy, when let out slowly, can be harnessed to generate electricity. When it is let out all at once, it can make a tremendous explosion in an atomic bomb.

A nuclear power plant (like Diablo Canyon Nuclear Plant shown below) uses uranium as a "fuel." Uranium is an element that is dug out of the ground many places around the world. It is processed into tiny pellets that are loaded into very long rods that are put into the power plant's reactor. The first

nuclear power plant to produce energy was the Obninsk Nuclear Power Plant in 1954 outside of Moscow in the former USSR.

The word fission means to split apart. Inside the reactor of an atomic power plant, uranium atoms are split apart in a controlled chain reaction. In a chain reaction, particles released by the splitting of the atom go off and strike other uranium atoms splitting those. Those particles given off split still other atoms in a chain reaction. In nuclear power plants, control rods are used to keep the splitting regulated so it doesn't go too fast.

If the reaction is not controlled, you could have an atomic bomb. But in atomic bombs, almost pure pieces of the element Uranium-235 or Plutonium, of a precise mass and shape, must be brought together and held together, with great force. These conditions are not present in a nuclear reactor.

The reaction also creates radioactive material. This material could hurt people if released, so it is kept in a solid form. The very strong concrete dome in the picture is designed to keep this material inside if an accident happens.

This chain reaction gives off heat energy. This heat energy is used to boil water in the core of the reactor. So, instead of burning a fuel, nuclear power plants use the chain reaction of atoms splitting to change the energy of atoms into heat energy.

Power plant drawing courtesy Nuclear Institute

This water from around the nuclear core is sent to another section of the power plant. Here, in the heat exchanger, it heats another set of pipes filled with water to make steam. The steam in this second set of pipes turns a turbine to generate electricity. Below is a cross section of the inside of a typical nuclear power plant.

1. Produces 1 helium atom, 1 neutron, and energy2. Causes a chain reacion3. Produces large amounts of energy4. Atomic bomb is an example5. Happens in the sun/stars6. Breaks large atoms into smaller atoms7. Combines small atoms into larger atoms8. Used since 19549. Will be used for energy in the future10. Uses Uranium, plutonium, and other heavy metals