power cannot be analyzed in satisfying detail at the present stage of development. Some may be far more tractable than those of fast breeders.

  • The complexity of problems in nuclear fusion may tend to isolate the scientific and technical community engaged in various aspects of this area of research and development. Care should be taken to ensure that this isolation does not lead to wrong decisions.

  • Research and development in nuclear fusion is expensive. To demonstrate the technology sufficiently for decisions about its use as a source of energy will cost $10–$20 billion. Each new possibility explored in the effort to optimize the fusion option will add to the cost.2 (The cost of developing any new long-term source of major significance, however, probably falls in the same range.)

THE FUSION REACTION

Large amounts of energy are released in the union or fusion of light nuclei. Nuclear fusion requires that two charged nuclei approach one another closely. They must approach with high enough energy to overcome their mutual electrostatic repulsion. High energy can be achieved through high temperature. The sun, for example, fuses hydrogen nuclei into helium at interior temperatures of about 20 million degrees Celsius. For the most promising earth-bound possibility—fusing deuterium and tritium into helium—temperatures about 10 times that of the sun’s core must be achieved and maintained long enough to allow a significant fraction of the fuel to react. At the high temperatures of fusion reactions, matter has decomposed into atoms whose electrons are stripped away. The result is an ionized gas, or plasma, that conducts electricity and responds readily to magnetic and electric forces.

The practical use of fusion as a source of energy, then, depends on the simultaneous achievement of high temperatures and effective containment of the plasma. Heating and containing the plasma, and operating the ancillary equipment that may be used to drive the reaction, represent a large investment in energy that the net production of energy from fusion must pay back with interest.

FUSION FUEL CYCLES AND THE ENVIRONMENT

The fusion reaction that requires the lowest temperature and the least effective containment, and offers the prospect of the highest power densities, is one of deuterium and tritium.



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