Energy From Thorium Discussion Forum

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PostPosted: Sep 19, 2013 11:07 am 
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Dave Mosher has a slew of articles up at Wired today regarding the lack of Pu-238 and it's effect on our space exploration. I think it could be a nice reference to point people to regarding the importance of nuclear technology in general and LFTRs specifically. There's even a nice interactive timeline with some video clips:

NASA's plutonium problem could end deep-space exploration
How the U.S. Tested the safety of nuclear batteries
Timeline: Plutonium 238's hot and twisted history
The best plutonium powered missions


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PostPosted: Sep 19, 2013 11:04 pm 
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Sr-90 has one-third the half life (30yrs) and could meet the requirement of shorter life missions. It could be easily separated from spent fuel.


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PostPosted: Sep 20, 2013 5:47 am 
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Sr-90 requires thick heavy shielding against bremstrallung radiation. It isn't a suitable replacement for Pu-238 for deep space missions.


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PostPosted: Sep 20, 2013 5:55 am 
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Kirk Sorensen wrote:
Sr-90 requires thick heavy shielding against bremstrallung radiation. It isn't a suitable replacement for Pu-238 for deep space missions.


What if you used a radiation resistant free piston stirling RTG, trailing behind the space probe on a leash? Use shielding in the rocket, then distance in stead of shielding in space?


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PostPosted: Sep 20, 2013 6:39 am 
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But then you have already lifted the shielding to orbit.


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PostPosted: Sep 20, 2013 7:46 am 
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E Ireland wrote:
But then you have already lifted the shielding to orbit.


Oh yes, of course. Then remove the shield just before launch? Just distance to shield. Rockets are tall. Deep space probes already need to deal with large levels of radiation. What exactly determines shielding requirements for a space probe?


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PostPosted: Sep 20, 2013 10:32 am 
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My comment to a post on the Planetary Society FB page last week:

Britain is looking into using Americium-241 for spacecraft batteries, instead of Pu-238.

http://www.bbc.co.uk/news/uk-england-cumbria-19550658

There are very large stocks of the former in spent nuclear fuel worldwide: As seen in the pie chart, there are nearly 5,000 Curies of Am-241 in every tonne of spent nuclear fuel from commercial power plants.
Every country that reprocesses their spent nuclear fuel is a potential supplier of this material: France, England, Russia, Japan.
And while Am-241 can be separated chemically from the spent fuel, Pu-238 cannot be separated from the large quantities of Pu-239, 240 & 241 also present in the mix.

https://dl.dropboxusercontent.com/.../1 ... WR_SNF.jpg


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PostPosted: Sep 20, 2013 11:53 am 
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Am-241 makes 114 W/kg.

Pu-238 makes 560 W/kg

Pu seems much better. Though if you only need a small amount of power, a few kg more or less isn't going to break the bank on your multi million dollar space probe.

AmO2 has a melting point of 1000C. The element isn't much higher. This might be a problem, though maybe not with that lower power density?


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PostPosted: Sep 20, 2013 1:28 pm 
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Remember NASA is close to perfecting the Radioisotope Sterling Generator.
That will seriously reduce the amount of material that has to be carried aboard the spacecraft for a given power output.

In the absence of permission to fly an actual reactor a lá JIMO this is the best that we can hope for.


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PostPosted: Sep 20, 2013 3:03 pm 
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E Ireland wrote:
Remember NASA is close to perfecting the Radioisotope Sterling Generator.
That will seriously reduce the amount of material that has to be carried aboard the spacecraft for a given power output.

In the absence of permission to fly an actual reactor a lá JIMO this is the best that we can hope for.


Yes, it saves about 75% on radioisotope (net efficiency of 28% versus 7%). But it's still 25%. Still need to get that. Lots of interesting deep space missions are being considered so demand is going up. Mars Rovers these days, are the size of cars, need loads of energy.

To heat a deep hole into the icy armor of Europa, however, will likely require a little nuclear reactor, or everything will just freeze back up again, if you have only a few kilowatts.

What form will Am-241 be in? It seems like the element is a better choice than the oxide; the element has a higher melting point and thermal conductivity.


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