Introduction to Nuclear Fusion

As the debate around the viability of nuclear power continues, particularly as the reality of the limitations of renewable energy sources become better understood, the advantages of fusion become ever more apparent:

• Abundance of the primary fuel, deuterium, which is one of the hydrogen isotopes. It can be readily extracted from seawater and tritium, another of the hydrogen isotopes originates from lithium which is readily available in the earth’s crust.
• Lower levels of radioactive waste than current fission reactors as there is no high-level waste, and any low level waste generated will not be of weapons grade nuclear material,
• Less radiation leakage as most fusion reactors will make less radiation than the natural background radiation of normal daily living.

Though there are no working fusion reactors in operation, there are a few in experimental stages at a number of laboratories around the world. In fact, a consortium of the U.S., Russia, Europe and Japan has formed to build the International Thermonuclear Experimental Reactor (ITER) to explore and demonstrate the feasibility of nuclear fusion technology.

Nuclear Fusion Reactions

Current nuclear reactors apply the principles of nuclear fission, where energy is produced by the splitting of an atom of uranium. In addition to yielding large amounts of energy, fission produces high levels of radiation and contaminated wastes which last many years. With fusion, energy is produced by the joining together of one of two hydrogen isotopes, deuterium or tritium, to form one helium atom, resulting in a process that is:

• Cleaner,
• Safer,
• More abundant, and
• More efficient than nuclear fission.

The challenge with fusion involves its very process, the combining of two nuclei of the same charge, similar in concept to placing the same poles of two magnets together: a natural repulsion. Thus to achieve fusion, special conditions must exist:

• Temperatures above 100 million Kelvin, 6 times hotter than the sun, are required to provide the hydrogen atoms sufficient energy to overcome the natural repulsion.
• Intense magnetic fields are required to increase pressure and literally “squeeze” the hydrogen atoms.

With today’s technology, these parameters can only be achieved with deuterium-tritium fusion. Deuterium-deuterium fusion is likely the best long term solution as it is easier to extract deuterium from seawater than to make tritium from lithium, deuterium is not radioactive and the combination will yield more energy. But the temperatures required to make this combination work are considerably higher.

And given, that these parameters can be met, there are two ways for hydrogen fusion to occur:

• Magnetic confinement, used in the ITER project in France, deploys magnetic and electric fields to heat and squeeze the hydrogen atoms. Accelerators formed from microwaves, electricity and neutral particle beams heat a stream of hydrogen gas, turning the gas into donut-shaped plasma. Super conducting magnets squeeze the plasma, enabling the occurrence of fusion.
• Inertial confinement, currently under investigation at Lawrence Livermore Laboratory in the U.S., uses laser or ion beams to heat and squeeze the hydrogen atoms. Current plans are to focus 192 laser beams on a pea-sized pellet of deuterium-tritium within a 10-meter diameter target chamber, heating the chamber and generating x-rays. The power from the lasers, estimated at 1.8 million joules, will convert the pellet to plasma, applying pressure until fusion occurs. The fusion reaction will last less than one-millionth of a second but provide almost 100 times more energy that required to initiate a fusion reaction.

In both methods of confinement, the heat generated will be passed through a heat exchanger to make steam that produces electricity.