[NukeNet] More on PU Shortage and NASA Missions

[Felice & Jack Cohen-Joppa]

Just for the sake of clarity, the Pu-238 used for thermoelectric 
generators is not the isotope used in weapons, and in fact is 
uncommon among the Pu isotopes, as it is not among the isotopes in 
waste from nuclear reactors and is cumbersome to produce and isolate: 
following is from the Wikipedia page:
http://en.wikipedia.org/wiki/Plutonium-238

"Plutonium 238, is a radioactive isotope of plutonium with a 
half-life of 87.7 years and is a very powerful alpha emitter. Because 
of its high level of alpha activity, it is used for radioisotope 
thermoelectric generators and radioisotope heater units. The use of 
plutonium-238 in American and Russian (and old Soviet Union) 
spacecraft is somewhat controversial.

"Plutonium-238 was the first isotope of plutonium to be discovered. 
It was synthesized by Glenn Seaborg and associates in 1941 by 
bombarding uranium-238 with deuterons. Neptunium-238 is made as an 
intermediate product, which then decays to form plutonium-238. 
Plutonium-238 decays to Uranium-234 and then further along the radium 
series to Lead-206.

"Today, Plutonium 238 is usually prepared by the irradiation of 
neptunium 237, a minor actinide produced in nuclear reactors, that 
can be recovered from spent nuclear fuel during reprocessing, or by 
the irradiation of americium in a reactor. In both cases, the targets 
are subjected to a chemical treatment, including dissolution in 
nitric acid to extract the plutonium-238. A 100kg sample of light 
water reactor fuel that has been irradiated for three years contains 
only about 700 grams of neptunium 237, and the neptunium must be 
extracted selectively.

"The United States currently has limited facilities to produce 
plutonium-238. Since 1993, the U.S. has purchased all of the 
plutonium-238 it has used in space probes from Russia. 16.5 kilograms 
total have been purchased.[1]"

Jack

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