A Radioisotope Thermoelectric Generator (RTG) is a simple electrical generator which is powered by radioactive decay. In an RTG, the heat is released by the decay of a radioactive material and converted into electricity using an array of thermocouples. RTGs can be considered a type of battery and have been used as power sources in satellites, space probes and unmanned remotes facilities such as lighthouses. RTGs are usually the most desirable source for unmanned and unmaintained situations needing a few hundred watts or less of power for durations too long for fuel cells, batteries and generators to provide economically and in places where solar cells are not viable.
RTGs use a different process of heat generation from that used by nuclear power stations. Nuclear power stations generate power by a chain reaction in which the nuclear fission of an atom releases neutrons which cause other atoms to undergo fission. This allows for the rapid reaction of large numbers of atoms, thereby producing large amounts of heat for electricity generation.
Chain reactions do not occur inside RTGs, so a “nuclear meltdown” is impossible. In fact, RTGs are designed so that fission does not occur at all; rather, forms of radioactive decay which cannot trigger other radioactive decays are used instead. As a result, the fuel in an RTG is consumed much more slowly and less power is produced.
In spite of this, RTGs are still a potential source of radioactive contamination: if the container holding the fuel leaks, the radioactive material will contaminate the environment. To minimize the risk of the radioactive material being released, the fuel is stored in individual modular units with their own shielding.
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