How did they machine the pu-238 for the nasa probe RTG's? - Page 1
Forum section: electronics / general

author: Beamin
author_rank: Super Contributor
timestamp: May 30, 2019, 09:28:01 pm
content: This is something I have been trying to figure out for a long time and the only thing I can find on the internet is this pictureImpressive to say the least this pellet goes inside a thermocouple but how do they make something that's red hot, can't be cooled and is incredibly reactive and dangerous? Pu in the pure metal form is pyrophoric meaning it will catch on fire in the air like sodium forming an oxide then a hydroxide which are salts and not suitable for this purpose.First you have to get the fuel out of the reactor, quite hazardous. Safe handling techniques aside, you have to separate it, normally this is done by dissolving in nitric acid in the case of Pu then simply using chemistry to refine it. That won't work if your solution boils away. Then some how when you have the metal you have to machine or form it into pellets, all the machine tools it comes in contact with become radioactive waste. Perhaps at red hot temperatures they can just crush it into the shape? You don't have to worry about heating it, but you can't let it come in contact with the air. The price of this stuff must be ridiculous considering just how much waste is made along with all the precautions and energy to make it. After trying to find this out for several years off and on, I do what I always do when I have exhausted all other resources and that is to ask the eevblog. We figured out how space dust is formed in a thread on the forum, which was pretty impressive.EDIT there is supposed to be a picture in this thread with img tags but its not showing, can you see it?https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator#/media/File:Radioisotope_thermoelectric_generator_plutonium_pellet.jpgWhile we are on the subject these things are just sitting around rural Russia with no safety or security concerns many have been looted killing the looter when it was found at a bus stop, which is now radio active waste. (sorry img tags not working)https://en.wikipedia.org/wiki/File:Soviet_RTG.jpg

author: dexters_lab
author_rank: Unknown
timestamp: May 30, 2019, 09:42:59 pm
content: my guess would be pressing a measured quantity into shape using a die, zero waste and only one tool needed

author: Kleinstein
author_rank: Super Contributor
timestamp: May 30, 2019, 09:51:12 pm
content: Clean PU-238 is in deed pretty expensive stuff - way more expensive than gold. It is highly radioactive, but not that dangerous, as it's mainly a alpha emitter, so shielding is relatively easy, though there can be secondary radiation (e.g. xray). The relatively low radiation level is what makes it so desirable. Shaping would be most likely by casting and maybe just forging.Handling oxygen sensitive stuff in special glove boxes with a pure argon atmosphere is pretty standard. This also helps with the radiation and contamination.Getting the pure PU-238 is not directly from reactor fuel, but from special "rods" containing Np-237 that are neutron irradiated in a suitable reactor. So the refining is different and much easier than starting from mixed fuel. The chemistry could be quite different than in normal reprocessing. It could use processes like electrolytic deposition from a molten salt mixture.It gets that hot only in larger units. So a shape like a wire or thin foil would be not that difficult to handle and cool.There may be an alternative way from the decay of some even heavier element.

author: Andy Watson
author_rank: Super Contributor
timestamp: May 30, 2019, 10:01:30 pm
content: Quote from: Beamin on May 30, 2019, 09:28:01 pmI assume that they cool it whilst working on it. The Pellet pictured on that wiki page had been kept insulated prior to taking the picture. Also, until the material is in its final pellet form it can be kept in a less dense state - which will lower the energy output.QuoteApparently it's an alpha emitter so it's relatively safe to handle - just don't get too close or eat it!QuoteIt's not used in its pure state, it's the dioxide form that is used. Essentially, it's already burnt.https://rps.nasa.gov/about-rps/about-plutonium-238/

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 30, 2019, 10:04:58 pm
content: It's PuO2, a stable ceramic. The powder is pressed and sintered.Same with nuclear fuel rods, UO2 pellets.Gosh, I wonder how they prepare the powder though. I'm sure it's precipitated from solution and calcined, or something like that. It would be wickedly toxic to get airborne dust of...Tim

author: apis
author_rank: Super Contributor
timestamp: May 30, 2019, 10:20:12 pm
content: Pure Pu-238 based plutonium dioxide is pretty safe, that's why it's being used in RTGs. It was produced at the weapon reactor sites, but that ceased after the cold war. Since the US has run out they have bought from Russia for about $8 million per kg, but Russia is also running out so there are some efforts to try and produce more now.

author: coppercone2
author_rank: Super Contributor
timestamp: May 30, 2019, 10:34:28 pm
content: search the forum for a thread about radioactive materials waste dumps. Everything you say about contamination is handled with bureaucracy and shady concrete. And later congress finds out.I wonder if NASA has a better track record then nuclear arms manufacturers.A primer:only 20 years after a major congressional hearing in the early 90's (other videos on youtube)

author: edpalmer42
author_rank: Super Contributor
timestamp: May 30, 2019, 11:33:34 pm
content: You've got the wrong URL for the picture. You're linking to the main article. Here's the picture:Looks cool! err hot! err you know what I mean!Ed

author: Beamin
author_rank: Super Contributor
timestamp: May 31, 2019, 12:57:37 am
content: Quote from: coppercone2 on May 30, 2019, 10:34:28 pmWhats always hard to figure out is how dangerous an isotope is. Such there was concerns of the reentry of the RTG used in the Apollo program so it was bolted to the leg of the lander and left on the moon. Shockingly Nasa has NO plans to clean up it's radio active waste that will be DANGEROUS for thousands of years!!! Also people are quite ignorant of radioisotopes so some of it is fear mongering.. But spread out over hundreds of miles and vaporized and it is still dangerous? Is cobalt 60 so dangerous that say a grain of sand sized amount of it is in a sand pile of 5 tons would that be dangerous?

author: dmills
author_rank: Super Contributor
timestamp: May 31, 2019, 01:30:18 am
content: Not sure you are right about that, my recollection was that the RTG was for the science package that was left on the moon, kind of the point. IIRC it powered the electronics for one of the seismology experiments.Apollo 13 (Where they never landed) had one of the considerations for the re entry profile being the desirability of splashing the Pu capsule into DEEP water in a subduction zone (The capsule was designed to survive reentry).You can broadly carve radioisotopes into three classes of half life, and only the middle one is really a problem from a radiation hazard perspective:VERY SHORT, meh who cares, it will never make it a hundred meters down the street.IN BETWEEN, yea can be an issue.VERY LONG, meh who cares, you need a fuckton of it to get a dangerous amount of activity.It is not things with 100,000 year half lives that scare me, it is the stuff with the 50 year half life.

author: Beamin
author_rank: Super Contributor
timestamp: June 01, 2019, 11:35:11 pm
content: Quote from: dmills on May 31, 2019, 01:30:18 amThat's why the iodine131 is so bad for a week after a meltdown. The RTG from Russia have strontium90 which is in the middle zone. I don't think most people make the connection that "hotter" isotopes "cool" down faster just like black body radiation. 2nd place for nasty is colbalt 60. There was a sample taken out of an abandoned cancer machine in mexico and the guy went through A LOT of trouble to get it out of the sheilding. He then gave his daughter it to play with since it was making blue cherenkov radiation in the air. Thats crazy when you can see the humidity lighting up in air, the blue glow inside the reactor can barely be seen because its underwater, let alone a vapor that is glowing so brightly! She died a few days later. It was so radioactive that they had to put a pallet of cement in front of it as they tried to pick it up with a machine. He contaminated a lot of things as he brought it home.

author: dmills
author_rank: Super Contributor
timestamp: June 02, 2019, 12:11:52 am
content: It was Brazil (Goiânia) not Mexico and was the perfect storm of feeding the fuckup fairy, but there have been half a dozen or so incidents with a mixture of medical and industrial sources.Edit: Turns out the Mexicans had something similar happen.There is actually new standardised labelling for the source capsule itself intended to make "Run away now or you die" rather more explicit then the standard radiation warning trefoil does, introduced after that incident.The relatively fast decay of the hot stuff is a GOOD reason to leave a life expired plant 50 years before trying to dismantle the business end, makes things much easier to deal with.Regards, Dan.

author: apis
author_rank: Super Contributor
timestamp: June 02, 2019, 12:24:07 pm
content: Quote from: Beamin on May 31, 2019, 12:57:37 amWhy is that?Quote from: Beamin on May 31, 2019, 12:57:37 amThat is the biggest problem, but it applies to all dangerous material (heavy metals, poisons, etc). If it's spread over a really large area it gets into everything and can accumulate in animals and plants and eventually get into humans. If it's just a few big chunks you can have a properly equipped team pick them up and put it away safely.Quote from: Beamin on May 31, 2019, 12:57:37 amYes. How dangerous depends on how much of the sand is between you and the cobalt though.

author: Beamin
author_rank: Super Contributor
timestamp: June 02, 2019, 01:06:03 pm
content: Quote from: apis on June 02, 2019, 12:24:07 pmIt was a joke. Leaving it on the moon will ensure it doesn't harm anyone. Its how people over react; I was reminded of this by the Julian Assange hack on NASA with the "wank" worm (W___something Against Nuclear Killers) When in reality his little stunt could have sent a rocket into a city and killed far more people then the small amount radiation safely contained on the space craft. Nuclear is the only way to save us from global warming and ironically nuclear plants are in decline because of environmentalists also no new plants have been built or designed since the 70's so we have much more dangerous plants. We should be using molten salt or pebble and/or thorium reactors that don't melt down. Or the time a mercury thermometer was dropped in a school and a hazmat team helicopters and the news showed up. We used to break them open as kids and play with it being sure not to touch it, we never got mercury poisoning.

author: apis
author_rank: Super Contributor
timestamp: June 02, 2019, 01:57:07 pm
content: Quote from: Beamin on June 02, 2019, 01:06:03 pmAhh, sorry. But what about the people at the moon base!Quote from: Beamin on June 02, 2019, 01:06:03 pmI think so too (and so domany others). There are those who claim we could reduce energy consumption instead but I don't see how. The population isn't going to shrink (maybe you could reduce childbirth with better information about family planing, condoms and such, but the influential Catholic Church is working against that and no one wants a global "one-child policy"). Poor people are getting better living standard (which is good) and that means they need electricity and heat. Problem is there is a limit to how fast the world can build new nuclear reactors too. Russia (I believe) and China (definitely, they need all the energy they can get) are expanding though. Would make more sense if high-tech countries build nuclear plants though, I would imagine they have less risk of cutting corners or screwing up something critical.Quote from: Beamin on June 02, 2019, 01:06:03 pmThat's another thing that's a bit counter intuitive. Mercury in it's elemental form isn't that harmfull, but it will react and form new compounds that are incredibly toxic, so if it gets into the environment it causes damage.