NASA’s Plutonium Problem Could End Deep-Space Exploration

http://www.wired.com/wiredscience/2013/09/plutonium-238-problem/all/

by hereonbusiness • 13 years ago

143 47 13 years ago

jlgreco5• 13 years ago

France has the resources to make Pu-238, though I am not sure if they currently have the facilities/equipment. If the situation really is politically impossible in the US and Russia keeps on flaking out, we could always try buying more from the French again and let them deal with the politics.

If we are shitcanning missions because we don't have Pu-238, then why doesn't NASA just take the money they would have spent on those programs and spend it on more Pu-238 instead? Surely that should buy us enough Pu-238 for at least remaining uncancelled missions.

maaku2• 13 years ago

If we are shitcanning missions because we don't have Pu-238, then why doesn't NASA just take the money they would have spent on those programs and spend it on more Pu-238 instead? Surely that should buy us enough Pu-238 for at least remaining uncancelled missions.

Requires an act of congress. Need I say more?

dalke6• 13 years ago

To elaborate on maaku's answer, as the article points out, "the Atomic Energy Act forbids NASA to manufacture plutonium-238."

zyb09• 13 years ago

Probably a non-issue, because more Plutonium-238 can be easily created using existing infrastructure. As demand of this stuff goes up and supplies dwindle, someone is gonna make more of it sooner or later.

maaku2• 13 years ago

There are legal constraints on Pu-238. Market forces do not apply, unfortunately...

spiritplumber• 13 years ago

Maybe they can use a box full of old pinball parts.

sliverstorm2• 13 years ago

Its production is verboten.

jevinskie2• 13 years ago

Every so often an atom of neptunium-237 absorbs a neutron emitted by the core’s decaying uranium, later shedding an electron to become plutonium-238.

Doesn't it shed a proton to become plutonium 238 and, as a consequence, loses an electron?

pjscott• 13 years ago

Proper description of what's going on:

http://en.wikipedia.org/wiki/Beta_decay

jevinskie2• 13 years ago

Thank you very much, I was under the impression that the electron was lost from the orbital cloud, not the nucleus!

Edit: Looking back at my math it was an off-by-one error in the wrong direction. :)

jlgreco5• 13 years ago

http://upload.wikimedia.org/math/5/5/7/557cb46ae9126680a7d57...

Basically one of the neutrons kicks out a beta particle and becomes a proton. The atomic number goes up but the mass number stays the same.

slacka• 13 years ago

Thorium reactors produce PU-238 as a “free” byproduct. One more reason we should be pursuing LFTR reactor research.

InclinedPlane• 13 years ago

Erm, sort of. It doesn't actually help that much.

As a short, but helpful, side discussion consider the breeding of Pu-239 in a reactor for use in nuclear weapons. Pu-239 works great in a nuclear bomb but other isotopes of Plutonium cause problems, specifically the high spontaneous fission rate of Pu-240 can create so many background neutrons that having a significant amount of it in a bomb can vastly increase the "pre-detonation" (fizzle) risk, which causes the bomb to have very low yield (on the same scale as the chemical explosives in the bomb). As Plutonium remains in a reactor subject to neutron flux it will naturally breed other isotopes, which is why there is a difference between weapons grade and reactor grade Plutonium. Reactor grade Plutonium can contain any variation of isotopes, essentially all of them are suitable for use in a reactor, but weapons grade Plutonium can only have a very small amount of Pu-240. And for this reason the way that weapons grade Plutonium is made is by removing fuel rods from a reactor on very short time scales and reprocessing it to remove the Plutonium then forming it back into new fuel rods and so forth. This is a very costly and complex endeavor which is why you can't just use ordinary power reactors for generating weapons grade Plutonium.

Interestingly, Pu-238 also exists in reactor grade Plutonium in substantial amounts (1% or more of the Plutonium, so nearly an entire tonne per year worldwide). However, because it's mixed up with all of the other Plutonium it would require extremely costly isotopic separation.

So, how is this relevant to Thorium reactors? Well, let's go back and look at what actually happens when Pu-238 is produced in a Thorium reactor. You start with Th-232, and under neutron flux you'll breed U-233, which is the reactor's main fission fuel. If U-233 is hit by a neutron and absorbs it instead of fissioning then you can end up with U-234, U-235, U-236, Np-237 (through a decay), and Pu-238 (through another decay). However, it's not as though things don't stop there. Pu-238 will breed into Pu-239, Pu-240, and so on, just as in a conventional Uranium power reactor.

So here you have the same problem as producing weapons grade Plutonium, you have a process that you need to stop before it goes too far, and in order to do that you need to pull the Plutonium out of the reactor at regular, short intervals. Otherwise you'll just get a buildup of ordinary reactor grade Plutonium. However, the problem is worse here because instead of being the product of just one neutron reaction (natural U-238 becoming Pu-239) the breeding of RTG grade Plutonium is the product of a long chain of reactions (taking 6 steps between the isotopes in the reactor fuel at the start and the production of Pu-238). This means the amount of production and the time scales of production are very much not helpful from the perspective of pure Pu-238 production, especially if you want to also operate a power reactor cost-effectively at the same time.

(Edit: also, there's an additional problem, because Thorium reactor fuel contains U-232, which has a short half-life and has decay products that are prodigious gamma ray sources, making reprocessing and handling even more difficult than ordinary reactor fuel. You can handle Plutonium in a glove box, but with used Thorium fuel containing U-232 you'd need to handle it via robotic manipulators in a heavily shielded area distant from humans, except that gamma radiation kills electronics like nobody's business, which is a bit of a catch-22. This is one of the key technical hurdles of Thorium reactor designs in general.)

In short, the fact that Thorium reactors produce Pu-238 isn't helpful, because existing reactors do too, but in either case it's hard to get at.

aidenn0• 13 years ago

This isn't specific to thorium, but could liquid fueled reactors allow for chemical separation of Pu-238, as it's the first Pu isotope in the chain?

Obviously the ability to do something like that is still far off; I'm not actually sure how we previously made usable Pu-238. Is it isotopic separation from breeder reactors?

tanzam753• 13 years ago

Contamination with plutonium-240 was a big problem during the Manhattan Project. They'd done the preliminary calculations based on cyclotron-produced plutonium-239, which was pure enough that a gun design with a long tube was feasible. ("Thin Man")

The plutonium-239 that came out of the Hanford reactor had a much higher contamination rate. This required a much faster assembly of the critical mass in order to avoid a fizzle. The gun design would have to be so long that it couldn't fit on a plane. Whereas implosion could provide the required rapid assembly in a limited space. Thus, "Thin Man" was out, and "Fat Man" was in. Implosion was no longer a secondary option -- it was the only option.

thangalin• 13 years ago

Directly related ("U.S. Starts Making Plutonium"): http://news.discovery.com/space/nasa-plutonium-production-sp...

ChuckMcM• 13 years ago

I was going to supply that link as well. We have been working on a restart for a while. Basically the Wired article is just silly.

greglindahl• 13 years ago

It's easy to read between the lines: The NASA guys think it's likely there will be problems, and that Congress will fail to act quickly when more money is needed.

guelo• 13 years ago

Actually DOE has started a production program using $10mil appropriated through NASA, http://spaceflightnow.com/news/n1303/20pu238/#.UjuOO6x3O4B

The original plan was to fund $10mil through NASA and $10mil through DOE for a total of $20mil per year, but DOE lost their half of the funding due to Solyndra-related politics.

dalke6• 13 years ago

You sound like you didn't read the linked-to article, which details all of that except for the Solyndra politics.

sliverstorm2• 13 years ago

There's no ambiguity here. He didn't.

robryan• 13 years ago

$10 million vs $20 million a year? It probably cost congress more to argue about this than the cut has saved.

molecule• 13 years ago

NASA’s Plutonium Problem Could End Deep-Space Exploration
By 2005, according a Department of Energy report (.pdf), the U.S. government owned 87 pounds, of which roughly two-thirds was designated for national security projects, likely to power deep-sea espionage hardware...

how about the U.S. government does less deep-sea espionage-- in the name of deep-space science?

rozap• 13 years ago

Wow you must be some kind of terrorist to even suggest such a thing.

Asterick6• 13 years ago

Useless comment, fade away.

pintglass2• 13 years ago

Heck, there's Google (https://www.google.com/maps/views/streetview/oceans?gl=us&hl...), Virgin Oceanic (http://www.virginoceanic.com/), etc. exploring down there. Nothing wrong with a little deep sea action- even the military contribute.

It's much cheaper to explore the ocean than it is to explore space, and many benefits like: OTEC (http://en.wikipedia.org/wiki/Ocean_thermal_energy_conversion http://cleantechnica.com/2013/05/05/lockheed-martin-to-build...), mining ( http://en.wikipedia.org/wiki/Deep_sea_mining), etc.

Others agree:

http://www.forbes.com/sites/quora/2013/01/31/why-dont-we-spe...

http://www.cnn.com/2012/04/09/opinion/etzioni-space-oceans/i...

But, I personally think we should be exploring space and our oceans. We need to make it a top priority of all countries to fund energy and propulsion research to help make exploration cheaper. That means allocating adequate budget and raising taxes for something that the mass media and our government doesn't seem to give much of a shit about, because they don't understand the part of the world we currently are utilizing is running out of resources quickly and that we are constantly a stone's throw from mass extinction.

madaxe3• 13 years ago

Espionage is not exploration, no matter what your congressman tells you.

The plutonium is for RTGs on benthic listening buoys, which are moored deep in the water column, or anchored directly to the sea floor. They have very sensitive hydrophones, and powerful burst ELF transmitters. This allows triangulation of targets.

They're made of steel and are never intended to be recovered - so we can look forward to plutonium salts in the oceans.

masklinn2• 13 years ago

You don't need Pu238 for deep sea exploration.

hereonbusiness• 13 years ago

It's actually really interesting what a relatively tiny amount of Pu-238 is needed to power deep space missions for decades, 36lb (16.3kg) of Pu-238 amounts to a sphere with a radius of 5.82cm according to wolfram alpha.

strictfp• 13 years ago

Political ignorance and shortsighted squabbling, along with false promises from Russia, and penny-wise management of NASA’s ever-thinning budget still stand in the way of a robust plutonium-238 production system.

Biased much?

runarb• 13 years ago

According to Wikipedia [0] it isn't all sorrows. There are other fuels available in large quantities at a low price, like Strontium-90 used in many Russian radioisotope thermoelectric generators. Other fuels like Americium-241 are also showing big promise, and are available commercially in large quantities. Americium-241 also has a much longer half-life, and can hypothetically power a device for centuries.

0: https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_ge...

NASA’s Plutonium Problem Could End Deep-Space Exploration

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