Fusion reactors: Not what they’re cracked up to be

But unlike what happens in solar fusion—which uses ordinary hydrogen—Earth-bound fusion reactors that burn neutron-rich isotopes have byproducts that are anything but harmless: Energetic neutron streams comprise 80 percent of the fusion energy output of deuterium-tritium reactions and 35 percent of deuterium-deuterium reactions.

Now, an energy source consisting of 80 percent energetic neutron streams may be the perfect neutron source, but it’s truly bizarre that it would ever be hailed as the ideal electrical energy source. In fact, these neutron streams lead directly to four regrettable problems with nuclear energy: radiation damage to structures; radioactive waste; the need for biological shielding; and the potential for the production of weapons-grade plutonium 239—thus adding to the threat of nuclear weapons proliferation, not lessening it, as fusion proponents would have it.

In addition, if fusion reactors are indeed feasible—as assumed here—they would share some of the other serious problems that plague fission reactors, including tritium release, daunting coolant demands, and high operating costs. There will also be additional drawbacks that are unique to fusion devices: the use of fuel (tritium) that is not found in nature and must be replenished by the reactor itself; and unavoidable on-site power drains that drastically reduce the electric power available for sale.

All of these problems are endemic to any type of magnetic confinement fusion or inertial confinement fusion reactor that is fueled with deuterium-tritium or deuterium alone. (As the name suggests, in magnetic confinement fusion, magnetic and electrical fields are used to control the hot fusion fuel—a material that takes an unwieldy and difficult-to-handle form, known as a plasma. In inertial confinement, laser beams or ion beams are used to squeeze and heat the plasma.) The most well-known example of magnetic confinement fusion is the doughnut-shaped tokamak under construction at the ITER site; inertial confinement fusion is exemplified by the laser-induced microexplosions taking place at the US-based National Ignition Facility.

Tritium fuel cannot be fully replenished. The deuterium-tritium reaction is favored by fusion developers because its reactivity is 20 times higher than a deuterium-deuterium fueled reaction, and the former reaction is strongest at one-third the temperature required for deuterium-only fusion. In fact, an approximately equal mixture of deuterium and tritium may be the only feasible fusion fuel for the foreseeable future. While deuterium is readily available in ordinary water, tritium scarcely exists in nature, because this isotope is radioactive with a half-life of only 12.3 years. The main source of tritium is fission nuclear reactors.

via Fusion reactors: Not what they’re cracked up to be | Bulletin of the Atomic Scientists

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