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#1 Crisp

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Posted 15 March 2013 - 14:39

To the stars: After a 25 year hiatus, NASA restarts plutonium production

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After a quarter-century hiatus, the United States has begun producing plutonium-238 once more. The decision was made to ensure that future NASA projects would have access to the valuable fuel. As US stocks dwindled, NASA began buying plutonium-238 from Russia, but that agreement came to an end in 2010. When most people think of plutonium, they think of nuclear weapons — but that’s not what plutonium-238 is used for.

If you need a power source that can last for decades, plutonium-238 is fantastically useful stuff. It’s got a half life of nearly 88 years and it emits 560 watts of heat per kilogram of material. It’s a vital component of the radioisotope thermoelectric generators (RTGs) used on Curiosity and in a number of space probes, including Cassini. One of the best features of plutonium-238 is that, while it’s radioactive as hell (275 times more so than plutonium-239, it takes a minimal amount of shielding to protect spacecraft or humans from contamination. Plutonium-powered pacemakers (yes, that was a thing for a little while) have operated as long as 25 years without running out of power.



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#2 DocM

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Posted 15 March 2013 - 18:11

It's about f'ing time!!

You can make RTG's from other materials, but there nowhere near as effective. There's a big one powering the Curiosity rover and many deep space probes that are too far out for solar to be practical.

#3 geertd

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Posted 16 March 2013 - 01:25

hmm i wonder if they could use this to power VASIMR

#4 Growled

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Posted 16 March 2013 - 03:20

So now maybe we can stop bumming the stuff from other countries.

#5 Torolol

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Posted 16 March 2013 - 03:29

what picture is that, why its red ?

#6 linsook

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Posted 16 March 2013 - 03:33

what picture is that, why its red ?


https://www.google.c...iw=1280&bih=662

#7 DocM

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Posted 16 March 2013 - 07:18

hmm i wonder if they could use this to power VASIMR


Radioisotope Thermoelectric Generators (RTG's) produce a few hundred to a couple thousand watts. VASIMR needs hundreds of thousands to millions of watts.

what picture is that, why its red ?


The plutonium oxide pellet above is red hot because of the heat of radioactive decay. Left in open air if wouldn't be that hot. Pics like that are done by putting the pellet in a graphite container, which causes it to get hotter, then removing it to snap the image. Its natural color is a yellowish to olive green.

#8 Growled

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Posted 17 March 2013 - 02:20

The plutonium oxide pellet above is red hot because of the heat of radioactive decay. Left in open air if wouldn't be that hot. Pics like that are done by putting the pellet in a graphite container, which causes it to get hotter, then removing it to snap the image. Its natural color is a yellowish to olive green.


Interesting info, Doc. Thanks. What happens if it's left in the graphite container?

#9 DocM

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Posted 17 March 2013 - 05:20

It stays red hot, the graphite acting as an insulator, and in an RTG the heat from Pu238 decay causes a surrounding thermocouple array to produce electricity. No or few moving parts, high reliability, and it has a half-life of 87.74 years.

In terms of radiation safety, Pu238 is an alpha emitter (high speed helium nuclei) which can be stopped cold by just a metallic casing, so minimal shielding is required. Impurities may add a slight beta (electrons) or gamma output, but they too can be effectively shielded. 2.5mm of lead is enough, and the casing is often its equivalent. Still best used in un-manned applications though.

Note that the yellowish to olive green color is for a plutonium oxide. Pure plutonium looks a lot like nickel or silver, but its brittle and it's not a good conductor.

#10 +virtorio

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Posted 17 March 2013 - 06:24

When people are talking about radiation I never have any idea what people are talking about, and yet, I still find it incredibly interesting.

#11 DocM

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Posted 17 March 2013 - 08:06

Ah - radiation. The oogie-boogie-man. The basics aren't that hard.

Matter is made of particles, mostly electrons (- charge), protons (+ charge), and neutrons (no charge), plus several dozens of others with similar charges. There is also electromagnetic radiation, which can be anything from radio waves, infrared, visible and ultraviolet light, to x-rays and gamma rays.

When we talk of "radiation" in the usual sense we're typically talking about high speed helium nuclei (alpha particles), electrons (beta particles), neutrons, x-rays and gamma rays.

The one thing these all share is that they can ionize atoms, meaning they can knock electrons out of ordinary atoms leaving them with a net + charge, which changes how it interacts with other atoms. If too many of these ionized atoms are in a living things DNA it cause problems; mutations, cancer or other health issues.

We run this risk even without nuclear power & such because of radiation sources in nature. Fly a plane, travel in space, go in most basements or underground, or even eat food grown in the Earth and you consume or are exposed to radiation sources. To a degree they even contribute to evolution by causing mutations. Radiation even streams through the atmosphere from deep space and the sun.

Mitigating this, cells have DNA repair mechanisms which help considerably, and there are medical teeatments in development that can be administered to help with many acute radiation sickness issues. Lots of work to do though.