Fusion Energy: Bringing the Power of the Sun to Earth
How Nuclear Fusion Works
Unlike nuclear fission, which involves the splitting of an atom into two atoms, nuclear fusion involves the fusion of two atoms into one atom. In a fusion reactor, in general, two hydrogen atoms are brought together to form a helium atom, a stream of neutrons, and a great deal of energy. There are several types of nuclear fusion reactions, most of which involve deuterium and/or tritium, isotopes of hydrogen.
A proton-proton chain reaction is the process by which stars like the sun generate energy. First, two pairs of protons fuse to form two deuterium atoms. Then each deuterium atom fuse with another proton to form a helium 3 atom. Two helium 3 atoms fuse to form a beryllium-6 atom. Then beryllium-6 decays to form two helium-4 atoms. This reaction produces a great deal of radiation and high energy particles.
A deuterium-deuterium reaction fuses two deuterium atoms to form a helium-3 atom, a neutron, and great deal of energy. A tritium-deuterium reaction fuses a tritium atom with a deuterium atom to form a helium-4 atom and a high energy neutron.
Thus, a nuclear fusion process is simple in concept/ However it is difficult to achieve under controlled conditions.
Conditions for Nuclear Fusion
The one problem with achieving nuclear fusion is that protons tend to repel one another, sort of like two magnets. To counteract this tendency, one has to apply high temperature and high pressure.
The temperature of a fusion reactor has to be about 100 million degrees Kelvin or about six times the temperature of the sun’s core. At this temperature, the hydrogen is a plasma, a state of matter in which electrons are stripped from atoms and move about freely. This temperature is achieved by using microwaves, lasers, and ion particles.Ã?¯Ã?¿Ã?½ Since hydrogen atoms have to be within 1×10 -15 meters on one another to fuse, a great deal of pressure, applied by magnetic fields, lasers, or ion beams have to be achieved.
The History of Nuclear Fusion
The theory of nuclear fusion was first developed by Robert Atkinson and Fritz Houterman in 1929, by measuring the masses of light elements and using Einstein’s famous E = MC2 formula to conclude that huge amounts of energy could be achieved by nuclear fusion. In 1939, Hans Berthe developed the quantitative theory explaining nuclear fusion that would win him the Nobel Prize in 1968.
Starting in the early 1950s, a series of reactors were built in an attempt to achieve controlled nuclear fusion. These experiments took place in the United States, the Soviet Union, Britain, and later Europe and Japan. By the 1990s, technology had advanced so that controlled fusion generating several megawatts of energy had been achieved for several minutes. While steady research has solved numerous problems, more keep being thrown up.
Currently, plans to construct a new fusion facility at Cadarache in France, called the ITER, have been finalized as a joint project of the United States, the European Union, Japan, China, Russia, and South Korea. Construction will begin in late 2005 or early 2006.
ITER
ITER stands for International Thermonuclear Experimental Reactor. It is also the Latin word for “the way.” It is intended to be an experimental step between today’s studies of fusion energy and future electricity-producing fusion power plants. It will cost 10 billion Euros to construct and operate. It is scheduled to begin operation in 2015 and will operate for twenty years. One of the goals of ITER is to achieve ten times the energy from a fusion reaction than has hitherto been achieved. It is designed to develop the technologies necessary for commercial fusion plants that will generate electricity, hopefully by the mid 21st Century.
Advantages of Fusion
Safe, reliable fusion power would increase the availability of energy ten or perhaps even a hundred fold. Fuel for fusion energy is readily available. Deuterium can be derived from sea water. Tritium can be extracted from lithium, a very common substance. Fusion reactions produce far less radioactive byproducts than do fission reactions. Like fission, fusion does not involve the combustion of fossil fuels and therefore does not contribute to water or air pollution. Fusion reactors do not have the danger of meltdown as do fission reactors and there is little or no possibility of catastrophic accidents of any kind.
Cold Fusion
In 1989 two chemists, Stanley Pons of the University of Utah and Martin Fleischmann of the University of Southampton in England claimed to have made a fusion reactor at room temperature without confining high-temperature plasmas. They constructed an electrode of palladium, placed it in a bath of heavy water (deuterium oxide) and ran an electrical current through the heavy water. The researchers claimed that the palladium catalyzed fusion by allowing deuterium atoms to get close enough for fusion to occur. However, the concept was held up to ridicule by the scientific community. Several attempts by scientists in other countries to replicate the cold fusion reaction failed to get the same result.�¯�¿�½
But in April 2005, cold fusion got a major shot in the arm. Scientists at UCLA created a fusion reaction using a pyroelectric crystal. They put the crystal into a small container filled with hydrogen, warmed the crystal to produce an electric field and inserted a metal wire into the container to focus the charge. The focused electric field powerfully repelled the positively charged hydrogen nuclei, and in the rush away from the wire, the nuclei smashed into each other with enough force to fuse. The reaction took place at room temperature. Research into the concept continues, though many scientists remain skeptical that cold fusion will every have any practical applications.
Helium 3 Fusion
Some scientists suggest that an even safer method of fusion would use as fuel an isotope of helium known as helium 3. Reactions fusing helium 3 atoms with other helium 3 atoms or with deuterium atoms would create energy without any of the radioactive neutron byproducts that characterize conventional fusion. Thus, a fusion reactor using helium 3 could be built in the middle of a city without any safety concerns.
There are two problems with helium 3 fusion. First, greater temperatures and pressures have to be brought to bear to start a helium 3 fusion reaction. Also, helium 3 does not exist in nature on Earth. The nearest source for helium 3 is on the surface of the Moon, where it has been deposited over billions of years by solar winds. Still, many people believe that the economics of helium 3 fusion would work, particularly give a human presence of the Moon. It is estimated that a shuttle bay full of helium 3 would satisfy the energy needs of the United States for a year. All it would take is the infrastructure to mine helium 3 from the Moon and transport it to Earth.
When Fusion Energy?
There used to be a joke that fusion energy was a technology that was fifty years away from reaching fruition-and always would be. But current advances in technology suggest that the first commercial fusion reactors may be available as early as thirty years in the future. By 2050, the world may be satisfying a major part of its energy needs with fusion power. By that time, the era of fossil fuels, with all of its disadvantages, would be history.
