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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."
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.
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.
AccountKiller
The Plutonium used by NASA is Pu-238, which is quite different from the weapons usable Pu-239. Pu-238 would melt its self to a liquid by its own alpha decay heat before long before you get a critical mass, thus Pu-238 is not weapons usable.
The Russians do not want to use it in a weapon. The Russians have been pushing for accelerated nuclear disarmament because they literally can't afford to protect & maintain all their nuclear warheads. The U.S. has been filling the gap by helping to cover the security costs (including stuff like rusting submarines sitting at the dock), but Russia still has serious security issues.
Read this to get a picture of the state of Russian nuclear storage
Keep in mind that Russia has many nuclear dump sites spread around the country & I doubt anything has changed since that article was written last year.
[Fuck Beta]
o0t!
I've heard a bit about these NASA and pacemaker RTG's which use plutonium-238. On the other hand, the much more widely-produced Soviet power RTG's (like the Beta-M) use strontium-90.
Any reason why we don't just use strontium--everybody makes that stuff. On the same note, why didn't the USSR use Pu-238?
not to be confused with Illudium Phosdex, the shaving cream atom found exclusively on planet X.
Plutonium-238 IS a fissile material and the criticality limits are similar to that of Pu-239. http://sti.srs.gov/fulltext/ms9900313/ms9900313.html
It doesn't make a good weapon trigger candidate since it has a fairly short half-life (decay products inhibiting the reaction), can get very hot on it's own (bad mechanically for the bomb itself), and the fission is fast and spontaneous (hard to control).
Most Pu-238 is stored as PuO, however since Pu-238 is a heavy alpha emitter it emits neutrons from the (alpha,n) reaction with O-17 & O-18. Therefore they try and selectively heat treat it so the vast majority of the oxygen isotopes are O-16. gloveboxes designed for Pu-238 still require several inches of dense hydrogenous shielding.
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.
All isotopes of plutonium are fissile, it's just that some of them are such strong neutron emitters that it's hard to make much of a bomb from them without predetonation sapping the yield, unless you've got a really good fusion boosted design. Some isotopes also give out a huge amount of heat due to spontaneous fission, making them unsuitable for bomb designs but great for RTGs, which is the real reason why NASA uses it: According to the Nuclear Weapons FAQ (http://nuclearweaponarchive.org/Nwfaq/Nfaq6.html#nfaq6.2), Pu-238 generates 567 W/kg due to radioactive heating. The NWFAQ mentions that for RTG purposes Pu-238 is normally generated by neutron bombardment of Neptunium-237, not by buying it from the Russians. Weapons-grade plutonium has only a miniscule amount of the stuff, and even reactor-grade isn't very rich in it. It's also hard to separate out since the mass difference compared to Pu-239, which is the main isotope, is so small.
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.
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.
You see? You see? Your stupid minds! Stupid! Stupid!
Sorry, no. The planet is named after the god, the element is named after the planet. You might have noticed that uranium and neptunium are also named after planets.
The comment to which you replied, and the grandparent, are not discussing the thermoelectric generators. They are instead discussing the breeder reactors which you need in order to process Uranium into Plutonium to create the fuel (plutonium) for the thermoelectric generators. It's like the difference between an oil refinery and an internal combustion engine - they are discussing the 'refinery', while you are discussing the engine.