Explain the meaning of Nuclear Fusion

Fusion happens when two light atoms like hydrogen or lithium combine. There is a net loss of mass which is converted to energy. The most familiar fusion reactor is our sun. It operates at a temperature of millions of degrees. This is called a thermonuclear reaction and is produced in an uncontrolled manner in an H-bomb with high temperatures generated by an A-bomb.

The idea of fusion is that two small unstable nuclei are smooshed together to make one larger stable nucleus.  This is the type of nuclear reaction which fuels the stars.  Hydrogen is built into helium at a temperature of millions of degrees.  

Two of the types of unstable helium are

Deuterium: 1 proton, 1 neutron ²₁H

Tritium: 1 proton, 2 neutrons ³₁H

One of the common hydrogen to helium fusion reactions in the sun is:

³₁H + ²₁H → ⁴₂He + ¹₀n

Fission vs. Fusion

A quick way to remember the difference between fission and fusion:

Fusion Fuses:  In the nuclear reaction, nuclei are actually fused together to make larger, more stable nuclei. 

Fission Fizzles:  Fission is the chain-reaction event which continues due to beta decay.  Each radioactive isotope fizzles to become more stable.

How does the fission of uranium compare to the fusion of hydrogen?  Strictly speaking, a single uranium fission event provides more energy than a single hydrogen fusion event.  But, compare the number of hydrogen molecules in a kilogram of hydrogen to the number of uranium molecules in a kilogram of uranium.  There are many more hydrogen nuclei than uranium nuclei.  Fusion of 1 kg of hydrogen atoms releases about 20 times more energy than a kilogram of uranium nuclei.  

Fusion Reactors:  

It is pretty difficult to achieve fusion in the laboratory.  A lot of energy is needed to initiate the fusion process and the reaction needs to proceed at a temperature of millions of degrees.  Scientist are just now at the break-even point.  The amount of energy needed to run the reactor is about the same as the energy removed.  

Large-scale fusion reactors are the dream of many energy scientists.   Fusion power plants would replace those now fueled by nuclear fission and fossil fuels. Because fusion power plants would not produce air pollutants they could minimize the environmental risks associated with the burning of fossil fuels and could substantially decrease demand for premium hydrocarbon fuels. Also, because fusion power plants would contain only small quantities of fuel at any time, they could eliminate the potential for runaway reactions that might lead to accidents. The development of low-activation materials or advanced fuel cycles for fusion reactors could make the amounts of high-level radioactive waste that result from fusion-produced energy far smaller than those produced by fission reactors, thus simplifying waste disposal problems.

Scientists are working on several ways to achieve controlled fusion for generation of energy. Tokamaks use magnetic confinement of the plasma. Laser fusion is another method being tried, as well as ion beam fusion. The tokamak is now near break-even, meaning that the amount of energy generated is equal to the amount of energy used to start and keep up the process. However, the other two methods are more likely to be developed into means of economically viable fusion energy generation.