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NASA completes full-power tests of small, portable nuclear reactor

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Re: NASA completes full-power tests of small, portable nuclear reactor

#91

Post by MertsA »

petra wrote: post #61
philipkglass wrote: post #45

Some background on this: NASA deep space missions have historically used radioisotope thermal generators powered by the decay of the exotic plutonium isotope Pu-238. This isotope has a good balance of lifetime (87.7 year half life) and specific energy (0.5 watts/gram). It is non-fissile -- no risk of criticality. It also decays solely by alpha emission, so there are no problems with shielding the rest of the systems…

The major fear that comes up with these is: what if the missile blows up while still in earth? How are these risks managed?

To simplify the other more detailed response, It's just Uranium at that point. Even highly enriched Uranium isn't that radioactive by itself, it's once you start operating the reactor that it starts generating highly radioactive waste.

The new fuel rods going into it are totally safe from a radioactivity perspective. Here's a picture of a man holding a fuel rod bundle with nothing more than gloves on. http://nuclearstreet.com/images/img/dw037.jpg

Re: NASA completes full-power tests of small, portable nuclear reactor

#92

Post by Theodores »

lightbyte wrote: post #49
HappyRobot wrote: post #5

Earlier quoted context omitted.

I think the drawback for space disposal is the risk of rocket failure. If a rocket explodes with nuclear waste on board, the waste would spread over a large area. It's safer at the moment to consolidate nuclear waste in small areas away from civilization.

>If a rocket explodes with nuclear waste on board, the waste would spread over a large area. Space is very big. Is it actually likely that said waste spreading would even be noticeable?

In the 1950s they thought that Nevada was very big and that the waste wouldn't even be noticeable.

They also thought the Pacific Ocean was very big and that the waste wouldn't even be noticeable.

Car drivers still think this way with their toxic emissions. It is very human to think 'out of sight out of mind' rather than 'take only photos, leave only footprints', so maybe it is actually fine to trash space with waste.

Re: NASA completes full-power tests of small, portable nuclear reactor

#93

Post by MertsA »

jabl wrote: post #79
TangoTrotFox wrote: post #71

Earlier quoted context omitted.

Something that's often left out in the discussion of nuclear because it's not an issue yet, is that nuclear fissile materials are also rare. If nuclear became the standard for energy production, the rarity of these materials would, in the longrun, end up creating more stupid games similar to what we play with fossil fuels today. 'Time do bring democracy to Australia!' 'Wait guys... what?? We are a democracy!!' 'Sorry…

It's usually left out of the discussion because it really is a non-issue long term as well. With breeder reactors (technology which already exists), Th in addition to U, U/Th extraction from seawater, we have enough fission fuel to power the entire planet at current levels for tens of thousands of years, if not indefinitely.

That's vastly understating the amount of Uranium and Thorium we can access. Without a breeder reactor it might only be tens of thousands but with a breeder reactor the amount of material we could use goes up by several orders of magnitude.

Re: NASA completes full-power tests of small, portable nuclear reactor

#94

Post by jarvist »

reaperducer wrote: post #78
jabl wrote: post #39

Earlier quoted context omitted.

The black helicopter people might arrive and have a nice chat with you when they discover you ordered a bunch of HEU from aliexpress.

Funny you should use the phrase "black helicopter." During the Cold War, the military used tiny nuclear reactors to power automated remote sensing stations in the Arctic. We called them "Power Pigs" and they were delivered by helicopter to very remote places. They were fascinating little devices, and because of where they were placed, used the outside air/ice/snow/rocks for cooling. Don't know if they are still being…

I guess these are the Strontium-90 RTGs made by the Soviets. There's about 1000 out there still - some have been vandalised, some washed out to sea, some sitting rusting in a lighthouse outhouse etc. http://bellona.org/news/nuclear-issues/radioactive-waste-and...

Re: NASA completes full-power tests of small, portable nuclear reactor

#95

Post by kss238 »

mcguire wrote: post #69
netzone wrote: post #4

What would the effects be of releasing nuclear waste in space? Could we sent up all of our nuclear waste, put a rocket on it and just let it disappear into the distance?

" All told, the nuclear reactors in the U.S. produce more than 2,000 metric tons of radioactive waste a year... " ( https://www.scientificamerican.com/article/nuclear-waste-let... ) Let's call it $20,000 / lb to orbit ( http://www.businessinsider.com/spacex-rocket-cargo-price-by-... ) and say double that for the "disappear into the distance" part. That gives us $160B to loft the US's nuclear waste for one year into n…

>Don't drop it

Is the unreasonable portion, not the cost.

Re: NASA completes full-power tests of small, portable nuclear reactor

#96

Post by Solarsail »

philipkglass wrote: post #45

Some background on this: NASA deep space missions have historically used radioisotope thermal generators powered by the decay of the exotic plutonium isotope Pu-238. This isotope has a good balance of lifetime (87.7 year half life) and specific energy (0.5 watts/gram). It is non-fissile -- no risk of criticality. It also decays solely by alpha emission, so there are no problems with shielding the rest of the systems…

Just a couple of asides, since I was reading about these very subjects (Am-241 RTGs and outer solar system photovoltaics) a few weeks ago;

The UK's NNL prototyped out a process for volume manufacture of Am-241 in 2013. http://www.nnl.co.uk/news-media-centre/news-archive/space-ba... And a few notes about the Americium-RTG effort more generally: http://www.planetary.org/blogs/guest-blogs/2015/0423-can-a-n...

NASA has also studied use of solar power beyond Jupiter's orbit: (PDF link) https://www.lpi.usra.edu/opag/nov_2007_meeting/presentations...

(Edit: Fixed a link)

Re: NASA completes full-power tests of small, portable nuclear reactor

#97

Post by dgoodell »

jjoonathan wrote: post #55
JTbane wrote: post #24

Pretty amazing that the simple Stirling engine can be the best choice for generating kilowatts of power in a hostile environment.

The magic comes from the nuclear half, not the Stirling half.

The free piston stirling engines required also operate via magic and few people understand them well enough to make one suitable for this purpose. The engines required for a reactor like this haven’t been designed yet and it would take years of effort before They would be designed and approved for flight use.

For this test they used a couple of undersized (<100W) stirling engines and the rest were just thermal simulators.

Re: NASA completes full-power tests of small, portable nuclear reactor

#98

Post by ajross »

jcims wrote: post #90
syntaxing wrote: post #7

For those curious, this uses a nuclear reactor to power a Stirling engine.Stirling engines are a good choice because there is no mass transfer to create the work (i.e. no fuel needed, just heat). It only needs a temperature differential and sealed gas/liquid to work. I highly recommend to read more about Stirling engines since they are of one the most efficient form of work generation with just a temperature differen…

Seems like this would be limited in space applications by how much you could radiate away. Wouldn't you need to get rid of ~2x the desired output power? So to get 1kW you'd need to dissipate ~2kW?

Yes. Though cooling sails are relatively feasible. Assume you can cool to ~250K: the back of my envelope and a Stefan-Boltzmann constant cribbed blindly from wikipedia tells me that such a sail would radiate ~200W/m^2, which is very doable for a spacecraft with a 1kW power budget.

Re: NASA completes full-power tests of small, portable nuclear reactor

#100

Post by nojvek »

nerdponx wrote: post #31
syntaxing wrote: post #7

For those curious, this uses a nuclear reactor to power a Stirling engine.Stirling engines are a good choice because there is no mass transfer to create the work (i.e. no fuel needed, just heat). It only needs a temperature differential and sealed gas/liquid to work. I highly recommend to read more about Stirling engines since they are of one the most efficient form of work generation with just a temperature differen…

Funny this should come up today. Just last night I was wondering why we don't have better technology for learning how to turn heat into electricity.

If our civilization figures out how to turn heat into electricity with a high efficiency and a small solid state device, it changes the economies of so many things.

But it’s a hard problem, mostly because of “entropy”.

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