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Name: Gregg
Status: Student
Grade: 12+
Location: NV
Country: United States
Date: Spring 2010

Why was mercury used in some radioisotope thermalelectric generators (RTGs)?

Hi Gregg,

After some extensive searching, I was unable to find a single reference to the use of mercury in a Radioisotope Thermoelectic Generator. Do you have any concrete examples of this? The only use for mercury I can imagine, is to act as a circulating cooling fluid.


Bob Wilson

The metal mercury was used in a Rankine cycle generator on the SNAP-1 RTG to make electric power. It was never deployed. Later RTG's seem to have used thermoelectric methods to generate the electricity. The Rankine system is similar to a steam power plant, but mercury metal is used instead of water. Mercury was found to be the best working fluid under the conditions and temperatures that space RTG systems operate. NASA tech note TN D-5092 has useful information how to make a mercury boiler for use in space. Nuclear reactors have also been used to generate power in space using a mercury Rankine cycle, but these are not RTGs. Russia has many RTGs rusting away all over their country, but I can find no evidence that they use mercury.

Robert Erck

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