Unlike plutonium-239 that is used to make nuclear bombs and of which the US possesses hundreds of tons, its close isotope plutonium-238 is a much rarer element.
With nuclear disarmament gaining momentum after the end of the Cold War, the US stopped producing military grade plutonium in 1992, with Russia shutting down its last military reactor producing plutonium-239 in 2010. But only Russia maintained industrial production of various isotopes of plutonium.
NASA’s plutonium poverty is a long-lasting problem. The US space agency used to buy the necessary radioactive element from the sole planetary plutonium producer Russia for years, but starting from 2009, when Moscow demanded revision of the old contract and hiked the price, the US stopped buying plutonium from Russia.
The US agency currently has just about 16kg of Pu-238, which isn’t much. The Curiosity rover’s ‘atomic heart’ consists of an RTG with over 4kg of the precious radioactive element, reports The Wired. But for example launched in 2006 New Horizons probe bound to Pluto right now travels through space with 11kg of the nuclear material on board.
NASA admits it has plutonium enough only till the end of this decade, but a number of missions have already been shelved entirely due to the lack of Pu-238.
Besides that, many military satellites also run on plutonium. As recently as August 28 this year, a Delta IV heavy rocket launched from the Vandenberg Air Force Base in California delivered to orbit huge KH-11 intelligence satellite for the US National Reconnaissance Office. Even if this satellite has solar panels, as any military installation it must have a reserve power supply, most probably an RTG.
On the off chance the Pentagon has some secret plutonium stash, it wouldn’t last long, simply because the US stopped its own plutonium production in 1988.
On top of all plutonium-238 half life is only about 87.7 years so the metal produced a quarter of a century ago has partly lost its energy potenti
Plutonium-238 is a radioactive isotope of plutonium that has a half-life of 87.7 years. Because it is a very powerful alpha emitter that does not emit significant amounts of other, more penetrating and thus more problematic radiation, often found with other forms of plutonium, this isotope is used for radioisotope thermoelectric generators (RTGs) and radioisotope heater units. One gram of plutonium-238 generates approximately 0.5 watts of power.
Pure plutonium-238 is prepared by irradiation of neptunium-237, one of the minor actinides 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 100 kg 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. Significant amounts of pure Pu-238 could also be produced in a thorium fuel cycle.
To produce plutonium-238 in a form less likely to undergo a chemical reaction and more safe for technological purposes near humans, the plutonium-238 isotope is reacted with water enriched with oxygen-16 to form 238Pu16O2. This compound generates fewer neutrons because oxygen-16 has a much lower (α,n) transfer nuclear reaction rate than do other isotopes of oxygen.
To answer your question: The ACP cannot be used to seperate PU-238 from U-238 because they both have the same atomic weight. The ACP seperates isotopes by weight which is why it can seperate U-235 from inert U-238.