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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

#111

Post by IdeaHamstir »

philipkglass wrote: post #109
jessaustin wrote: post #102

Earlier quoted context omitted.

One can't help but notice from his shirt and his hair that the picture was taken in the 1970s. Lots of awful practices still existed then; who's to say this isn't a picture of that?

Here's a photo series from 2005 at a Swedish nuclear fuel facility showing how uranium turns into fuel pellets and fuel rod bundles: https://www.iaea.org/newscenter/multimedia/photoessays/train... At all stages the material can be handled with no more protection than gloves. It is roughly as dangerous as handling lead fishing weights until the fuel actually attains criticality.

It still produces a fair bit of alpha, so avoid particulate ingestion.

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

#112

Post by IdeaHamstir »

larkeith wrote: post #107
ausjke wrote: post #66

can this be used for car/boat/etc-fuel somehow one day, then all gas-station will be run out of business and middle-east-plus-texas-oil-field all file for chapter-11? not sure how to prevent radiation though.

There's a few problems with making Highly-Enriched Uranium commercially available, even before we get to radiation. Thorium reactors [1], on the other hand, might be more feasible due to their lack of weaponization potential, cheaper fuel, and reduced waste. However, Thorium reactors are much more complex, and will likely never approach the small scale of KiloPower; they also have significant startup costs, remain co…

They have completed designs using low enriched Uranium. They're not quite as elegant or as small, but they should work fine.

https://fas.org/nuke/space/leu-reactor.pdf

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

#113

Post by caf »

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…

You can buy little coffee-cup-powered Stirling engine tchotchkes.

https://www.youtube.com/watch?v=CSgo9NSyFPs

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

#114

Post by kamaal »

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?

I thought everything, including our bodies were made up of nuclear waste from stars.

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

#115

Post by TangoTrotFox »

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.

You can't just handwave away the economics or practical issues here. Seawater extraction is incredibly expensive. Breeder reactors are also expensive, ignoring the countless other technical and practical issues that they come with. For instance the output level for optimal efficiency with breeder reactors is quite low. You'd have literally thousands of breeder reactors spread around (with a proportional number of fuel reprocessing plants) when you run into the practical problem that, while failure rates are low, with the number of facilities scaled up by orders of magnitude they are currently intolerable due to the consequence of failure.

But back to cost your argument is like saying that "Bah, there's no concern about a lack of freshwater. We can just desalinate the sea!" You sure can, but that's completely irrelevant as the costs make it an unreasonable solution. Using conventionally obtained and utilized material, we only have enough nuclear material for about 200 years of consumption. [1] And in looking at the longrun it's obviously quite myopic to take as an assumption that humanity has reached the highest energy usage it will ever have.

[1] - https://www.scientificamerican.com/article/how-long-will-glo...

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

#117

Post by jgamman »

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…

Ormat does large Stirling engines for geothermal power. The binary units mean you don't run the risk of taking too much of the reservoir fluid. I wouldn't be surprised if tech like this ramps up for the same reason battery tech went nuts when people wanted longer life electronics - except the driver is climate change and carbon pricing.

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

#118

Post by Doxin »

chiph wrote: post #110

How do they manage to not have the reciprocating mass (the piston) throw off a space vehicle's trajectory? IIRC the Space Shuttle used magnetic tape because a hard drive would have acted as a gyroscope.

Keep in mind that in the space shuttle era hard drives were a good deal more massive than today. Presumably a modern hard drive wouldn't present much of a problem.

In any case a rotating mass isn't too big of a problem, it's changes in rotational speed that'll mess with your heading -- not your trajectory though. The piston itself shouldn't be too much of a problem either because any motion it makes one way it shortly after makes the other way balancing out the forces over time.

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

#119

Post by taejo »

inamberclad wrote: post #105
jcims wrote: post #90

Earlier quoted context omitted.

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?

The upper limit of any heat engine (turning heat into useful work) is called the Carnot efficiency and is limited by the temperature differential. It's usually not more than 70%, though for a Stirling engine, a few percent would be considered excellent efficiency. A Stirling engine easily needs to radiate 20 times as much heat as it produces as power.

> for a Stirling engine, a few percent would be considered excellent efficiency.

Wikipedia says "Stirling engines have a high efficiency compared to internal combustion engines, being able to reach 50% efficiency," which seems to contradict that. What's the discrepancy?

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

#120

Post by hatsunearu »

taejo wrote: post #119
inamberclad wrote: post #105

Earlier quoted context omitted.

The upper limit of any heat engine (turning heat into useful work) is called the Carnot efficiency and is limited by the temperature differential. It's usually not more than 70%, though for a Stirling engine, a few percent would be considered excellent efficiency. A Stirling engine easily needs to radiate 20 times as much heat as it produces as power.

> for a Stirling engine, a few percent would be considered excellent efficiency. Wikipedia says "Stirling engines have a high efficiency compared to internal combustion engines, being able to reach 50% efficiency," which seems to contradict that. What's the discrepancy?

Yeah, even thermoelectric piles (Peltier effect devices) can easily get ~~double digit efficiencies. Not sure what that guy is talking about~~.

Thermoelectric piles are basically the worst form of generating electric power with heat (it has 0 moving parts, so it's used in various places), and it's still not that bad.

edit: Never mind, apparently they are worse than what I thought they were, at 5~8%. But they are still the least efficient way to turn heat into electricity, and yet they can achieve what that guy said.

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