Energy Sciences

Fusion

The benefits of controlled fusion are that a tremendous amount of energy is produced based on the conversion of mass into energy (E=mc ²) by combining heavy hydrogen (protons with extra neutrons) together to create helium! Nuclear energy releases nearly inconceivable amounts of energy. Compared to chemical bond energy, the creation of one helium nucleus from four hydrogen nuclei releases 10 million times the energy of the burning of 2 hydrogen molecules with oxygen to form water! Ideally this process produces no radioactivity (unlike nuclear fission- which is the breaking apart of large atoms, such as uranium-235, into isotopes that are radioactive for tens or hundreds of thousands of years).(3) Ideally, water, using thermonuclear fusion, could power the world! The sun combines four protons in the form first of deuterium atoms; deuterium (D) is a hydrogen isotope with one neutron. In this reaction, one of the protons releases a positron, thus becoming a neutron and conserving charge. Then the deuteron collides with a proton forming helium-3… this entire reaction occurs twice. The two helium-3 atoms collide, releasing two protons and forming helium-4. The collisions occur at solar temperatures around 14 million degrees within the sun's core resulting from the Sun's gravitational Force. The 4 hydrogen atoms form a helium atom with less mass and based on the famous equation E=mc ², millions of electron volts are released in each reaction, with no resultant radioactivity. However the reaction takes a million years. This is good for us, otherwise the sun would have burned up by now!(4)

On earth there are some additional challenges, in addition to the fact that we cannot wait a million years! The gravitational force of the sun is immense and cannot be replicated here, so instead of 10 million degrees, the reaction requires several hundred million degrees! Currently, the process that is used combines two isotopes of hydrogen. The first is a deuterium isotope of hydrogen, a proton with one neutron, which can be found readily within salt water at the rate of approximately 1 deuterium per 6500 hydrogen on earth.(5) The second isotope is tritium (T), which is a heavier isotope of hydrogen with 1 proton and two neutrons. Tritium can be produced by bombarding a lithium atom, which is prevalent on earth, with a high-energy neutron, splitting the lithium atom into a helium nucleus (known as an alpha particle) and a tritium isotope, in a reaction that requires 2.5 MeV. This can be written as: ⁷Li+n—> ⁴He+T+n-2.5MeV. So, if neutrons are desirable for a breeder reaction, then ⁷Li can be used and, as long as energy is supplied, more tritium can be produced. Finally, the overall fusion reaction involving deuterium and tritium can be written as: D+ T —> n (14.1 MeV) + ⁴He (3.5 MeV).

http://www.lbl.gov/abc/wallchart/chapters/14/2.html

It should be mentioned, however, that fusion results in 1/10 ^th the energy per reaction that splitting a U ²³⁵ atom does, as a result of the difference in mass conversion. The benefit is that there is virtually no radiation (except the radiation that results from the high-energy neutrons hitting the inside of the reactor and the lithium breeder reactor of the tritium, which has a half-life of 12.3 years.) For all practical purposes, there is an unlimited supply of fuel for fusion. An additional advantage to fusion is that there isn't the possibility of an accident that would result in massive radioactive contamination as in fission. The failure of a fusion reactor at worst would result in an explosion of the reactor because of the uncontrolled release of the high-temperature plasma, but the dissipation of the plasma cannot result in a further reaction. It is even suggested that in the current designs of ITER (International Thermonuclear Experimental Reactor) that such an explosive event is not possible.