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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

#101

Post by larkeith »

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…

A Stirling engine supplied by sodium heat pipes [1][2], even! It's a fascinating design of closed-cycle engineering, with minimal moving parts.

[1] https://en.m.wikipedia.org/wiki/KRUSTY

[2] https://en.m.wikipedia.org/wiki/Heat_pipe

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

#102

Post by jessaustin »

MertsA wrote: post #91
petra wrote: post #61

Earlier quoted context omitted.

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://nuclears…

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?

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

#103

Post by larkeith »

Theodores wrote: post #92
lightbyte wrote: post #49

Earlier quoted context omitted.

>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.

This... isn't really relevant for space. The amount of emptiness so massively outweighs the quantity of matter and energy it would be literally impossible to utilize a nontrivial portion of the volume available.

The only case in which releasing waste into space is problematic is when it's within a highly-utilized area, for example LEO. In the future, we may potentially use various transfer orbits and/or the Interplanetary Transport Network [1], so we should presumably avoid dumping there, but even within the solar system, the sheer volume of vacuum dwarfs any possible use.

[1] https://en.wikipedia.org/wiki/Interplanetary_Transport_Netwo...

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

#104

Post by larkeith »

dukoid wrote: post #9
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?

How about just sending it to the moon instead? Perhaps then we could use the moon as a giant space ship by blowing up the nuclear waste?

Nuclear waste is just that - waste. It's generally no longer capable of supercriticality.

Nuclear explosions as a method of space propulsion is a viable idea [1], however. (Using the Moon would be rather inefficient though.)

[1] https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propuls...

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

#105

Post by inamberclad »

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?

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.

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

#106

Post by jjoonathan »

dgoodell wrote: post #97
jjoonathan wrote: post #55

Earlier quoted context omitted.

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 simula…

Stirling Engines exceed their competition by percentage points. Nuclear energy exceeds its competition by orders of magnitude. I stand by my statement that the magic comes from the nuclear half of this relationship -- so long as we accept a definition of magic related to, you know, energy production, rather than effort or hipster points.

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

#107

Post by larkeith »

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 commercially unproven, and have a more dangerous fuel cycle (in terms of radioactivity).

[1] https://en.wikipedia.org/wiki/Thorium-based_nuclear_power

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

#108

Post by larkeith »

forkandwait wrote: post #37

So... Are plans available anywhere?

Link [pdf] to NASA's Kilopower Project media slides, which includes the design (not full plans, but close enough) [1].

[1] https://www.nasa.gov/sites/default/files/atoms/files/kilopow...

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

#109

Post by philipkglass »

jessaustin wrote: post #102
MertsA wrote: post #91

Earlier quoted context omitted.

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://nuclears…

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.

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