A new type of jet engine powered by laser-triggered nuclear reactions is the subject of a patent filed by Boeing on 30June. The engineers claim that the engine could be highly efficient once created, harvesting energy from the thruster chamber to power the laser.
In essence, a controlled nuclear explosion gives the vehicle thrust. A coated fuel pellet containing tritium and deuterium is placed at a laser focal point within the thrusters’ cavity. As is typical in laser fusion reactions, compression of the fuel cell through the ablation of its coating by the laser creates high enough temperatures within the fuel core to cause fusion of the deuterium and tritium fusion. This produces waste gases, most likely helium, and neutrons.
The exhaust gas produces the thrust to drive the engine forward, but the neutrons could be used to make the system highly efficient. The team proposes to include uranium-238 in the thruster walls. When the neutrons from the fusion reaction come into contact with the uranium, they trigger fission reactions. The heat from these fission reactions can be recovered by techniques similar to those used in a civil nuclear power plant and used to drive a turbine in order to power the laser that triggers the fusion reaction.
The engine exists only as a patented design. Laser fusion has been achieved only in very large laboratories using huge lasers, both in terms of their physical size and their power.
Researchers currently experimenting with fusion have had to build entire facilities to create the reactions. The Nuclear Ignition Facility in California, USA, requires 192 laser beams to ignite a Deuterium-Tritium fuel cell within a 10 metre diameter ignition chamber. The Laser Mégajoule site near Bordeaux, France, plans to unleash nearly 2MJ of energy on a fuel pellet to start and hopefully maintain a fusion reaction once operational, estimated to be sometime next year.
The fission element means that the whole engine would be radioactive and would generate ‘fission products’ which can have half lives of thousands of years and be dangerous as a result of their biological activity. (Radioactive caesium and strontium, for example, lodge in the bones and thus continue to irradiate the victim.) Thus a crash could spread highly radioactive material into the environment. Regardless of the fissionable materials, it is also unclear whether the occupants of the aircraft would be adequately shielded from the neutron radiation given out by the fusion reaction.
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