NASA Running Out of Plutonium

PRB_Ohio takes us to Space.com for a story about NASA's plutonium shortage, and how it may affect future missions to the far reaches of the solar system. The U.S. hasn't produced plutonium since 1988, instead preferring to purchase it from Russia. We discussed the U.S. government's plans to resume production in 2005, but those plans ended up being shelved. If NASA is unable to find an additional source, it could limit missions that take spacecraft too far from the Sun. Quoting: "Alan Stern, NASA associate administrator for science, ... said he believed the United States had sufficient plutonium-238 on hand or on order to fuel next year's Mars Science Lab, an outer planets flagship mission targeted for 2017 and a Discovery-class mission slated to fly a couple years earlier to test a more efficient radioisotope power system NASA and the Energy Department have in development. To help ensure there is enough plutonium-238 for those missions, NASA notified scientists in January that its next New Frontiers solicitation, due out in June, will seek only missions that do not require a nuclear power source."

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The 2 ways to obtain Pu-238

[extract]

There are currently 2 ways for US to obtain Plutonium-238 for space flights without buying it from abroad: 1. Use nuclear waste. Laser Isotope Seperation (LIS) is needed to seperate the Pu-238 from the other isotopes. 2. Breed on Neptunium-237. It is also found in nuclear waste, however it is easily separated from the rest. It can be bred into Pu-238 in a breeder blanket in a reactor.

Re:This is an opportunity

[Vellmont]

Second, many people should rejoice, this is a golden opportunity to decommission a warhead or two for the plutonium in it.

No dice.

Nasa uses Plutonium-238 in it's RTGs because it's a strong alpha-emitter, and has a short half-life on 87 years. I also believe it's non-fissile (meaning it can't be used for an nuclear weapon).

Plutonium-239 is the stuff they use in nuclear weapons, and it's fairly useless as an RTG generator.

Re:WTF?

[NeverVotedBush]

Hey all - there is a very important concept to this discussion that most don't seem to be aware of.

Pu239 is the isotope of plutonium that is used in weapons. It has a very long half life (~24,000 years) and works great in nuclear weapons since it releases neutrons when the nucleus breaks apart and those neutrons cause other nuclei to break apart as well in a massive chain reaction that releases huge amounts of energy. (Normal decay path is through alpha particle emission (helium nuclei))

Pu238 is the isotope used in thermoelectric energy generators. It has a relatively short half live of ~88 years. Because of the shorter half life, it is a lot more radioactive than Pu239. The nucleus spontaneously undergoes alpha decay and releases enough energy frequently enough that chunks of this isotope glow red from the heat.

The plutonium used in warheads cannot be used in thermoelectric generators and vice versa.

More Info On Plutonium

[NeverVotedBush]

If you want to read an excellent discussion of reactor vs. weapons grade plutonium (though there isn't much information on Pu238 for thermoelectric generators) go here: http://www.globalsecurity.org/wmd/intro/pu-isotope.htm

Methods used to make the two isotopes (weapons grade Pu239 vs. thermoelectric generator Pu238) are quite different.

Pu239 is produced from U238 when it absorbs a neutron and decays to Pu239.

Pu238 is produced with U235 through a chain of neutron absorptions and decays.

U238 is the more common form of uranium and is not the kind used for uranium weapons. Relatively pure U235 is what is frequently called highly-enriched uranium (HEU) and is the kind used for weapons.

Re:WTF?

[Junior J. Junior III]

Right, the Russians want to dismantle the weapons and not have to maintain them or protect them. Problem is, what do they do with the Pu once the weapons have been dismantled? Answer: sell it. But to who? Unsavory guys who'll make it into weapons, or US Science Guys who promise not to? The Russians and US both think it's better for the Pu not to be made into weapons, so we have the arrangement. If we didn't take it, someone would need to do something with it, and who knows what that would be -- probably not something the US would like.