Fusion

And what about fusion? At this stage (and into the foreseeable future), it is far from commercially attainable, but there is enormous interest and activity in laying the groundwork for future fusion energy generation. A long sought-after goal, energy from nuclear fusion is attractive for its ability to maximize the power output while minimizing the generation of nuclear waste. The source of energy is the fusion of deuterium and tritium to form helium (Equation 9.18):

?H + 3H ^ *He + 0 n (+17.5 Mev) (9.18)

The amount of energy released from this reaction is 3.5 MeV/nucleon (compared to 0.5 MeV/nucleon for a typical fission reaction (Irvine 2011)). There is no genera­tion of carbon dioxide or other greenhouse gases and no possibility of an uncon­trolled reaction. Furthermore, with the absence of Pu-239, the concern of nuclear proliferation is also absent.

Unfortunately, it takes Sun-like temperatures to initiate the fusion reaction (over 100 million degrees Celsius)! While this is easy enough to attain in the form of the hydrogen bomb, creating nuclear fusion in a controlled manner for generation of electricity is a severe technological challenge. In addition, the economic challenge is so great that to build a fusion reactor will require international cooperation. Such a cohort has been formed between India, the European Union, Russia, Japan, the United States, China, and Korea under the acronym ITER: the International Thermonuclear Experimental Reactor (http://www. iter. org/). The ITER project is in the process of building a prototype fusion reactor that plans to produce 500 MW output from 50 MW input. Construction began in southern France in 2010 with full operation targeted for early 2027.

The key to the ITER project is magnetic confinement of the fusion materials in a tokamak vessel (Figure 9.12). In a torus-shaped chamber, the deuterium and tri­tium nuclei will be heated under vacuum to temperatures above 150 million degrees Celsius, forming a gaseous mixture of positive ions and electrons (aplasma) in which fusion can occur. By the use of extremely strong magnetic fields, the plasma can be concentrated and held in the center of the torus so that no material touches the walls.

FIGURE 9.12 (See color insert.) The ITER tokomak fusion reactor. (From http://www. iter.

org/doc/all/content/com/gallery/Media/7%20-%20Technical/In-cryostat%20Overview%20 130116.jpg)

If the plasma did make contact with the walls, the reaction would instantly cease and the material of the wall would be destroyed.

While fusion energy is appealing from the viewpoint of safe and sustainable nuclear power, this approach is astronomically challenging and expensive. Any sort of large-scale implementation of fusion energy is many decades away.

Updated: September 26, 2015 — 6:02 pm