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Fusion

Most nuclear power, including all current commercial nuclear reactors, uses nuclear fission—the absorption of a neutron by an atomic nucleus, resulting in its splitting into two or more smaller nuclei. Fusion power, which has been pursued experimentally since the early atomic age in the 1950s, generates power instead through nuclear fusion in which two atomic nuclei fuse together to form a single, heavier nucleus, releasing energy in the process. As with fission reactors, most fusion power plant designs use nuclear fusion to generate heat, which operates a steam turbine, which in turn drives generators to produce electricity. Fusion power has successfully been generated in small amounts. However, a fusion power plant design had not yet been devised and implemented as of 2010 that was efficient and commercially viable. This is in contrast to the brief period from the inception of fission power to its first commercial applications, which took less than a decade.

Fusion Designs

Early fusion power research revolved principally around the idea of the “pinch,” the compression of plasma by magnetic forces. When an electric current is run through plasma, a magnetic field is generated, which creates an inward-directed force that causes the plasma to collapse and become more dense. Denser plasmas then create denser magnetic fields, increasing the inward force further in a chain reaction. Carefully controlled, this can generate the right conditions for nuclear fusion. However, even running the current through the plasma in the first place is no simple task; usually, it is induced by an external magnet. Pinch devices were used experimentally in the 1940s and 1950s, including the imaginatively named “Perhapsatron series” of fusion power devices developed at the Los Alamos National Laboratory in 1952. However, the Perhapsatron devices, like other pinch devices, became unstable at critical points, and beginning in the mid-1950s, the suggestion was made that pinch devices might be inherently unstable. Most work on them ended by the 1960s, but the flurry of experimentation and exchange of ideas laid the groundwork for fusion research.

Various other designs have been attempted since. Some fusion designs attempt to reach a level of high temperature and density for a short period, like the pinch designs or the inertial confinement devices, which initiate fusion through heating and compressing a fuel pellet. One such inertial confinement fusion device was designed by Philo T. Farnsworth in 1968, 40 years after his invention of the electronic television. Inertial confinement remains one of the two most popular areas of fusion research; the other is magnetic confinement, which attempts to confine hot fusion fuel in the form of plasma and maintain a steady state. Occasionally, there is also work on devices that approach fusion from neither of these angles, but instead focus on producing low quantities of fusion at a low cost. While physically possible, these approaches have not proven fruitful or to have many useful applications. The term low cost is relative to the cost of the larger fusion power plants, not to other existing energy options.

Safety and Containment

The safety of nuclear fusion was not fully understood as of 2010 because of the lack of full-sized fusion power plants and the ability to study their operations. However, because of the differences between nuclear fusion and nuclear fission, the catastrophic accident that fission reactors are capable of (such as experienced in Chernobyl in 1986) is not a possibility with a fusion reactor. Fusion reactors require precise temperature, pressure, and other parameters in order for energy to be produced. Damage to the reactor would upset those parameters and cease the production of energy. Fission reactors, in contrast, produce fission products that will continue to generate heat even after the reactor is shut down, which can result in a meltdown of fuel rods as heat accumulates. The dangers of a fusion reactor would involve radiation exposure of staff and the release of radiation to the immediate vicinity but not the calamitous disasters of a Chernobyl-like incident. Further, unlike the fission reaction, the fusion reaction cannot “run away” and produce excess heat and waste products—fusion only works in a narrow window of parameters and exceeding them will simply result in the fusion process ceasing. No failsafe mechanisms such as the many implemented in fission reactors are necessary; further, the amount of fuel used is very small.

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