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

engadget.com

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

#81

Post by InclinedPlane »

Sir_Substance wrote: post #8

Conspicuously not mentioned: what kind of design the reactor uses. Thanks engadget, 10/10 reporting. Based on the wikipedia article, it looks like a passive decay heater attached to a bunch of sterling engines. Pretty much a souped up RTG that trades more energy output for having moving parts. Neat.

No, it is a reactor not an RTG.

It is self-regulating (load following) to some extent so it doesn't have many moving parts. It has two main control mechanisms: a neutron absorbing control rod and a Beryllium neutron reflector.

Lots of details here: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/201400...

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

#82

Post by InclinedPlane »

linuxguy2 wrote: post #32
zaroth wrote: post #10

Earlier quoted context omitted.

That is in fact precisely what it is designed for.

Isn't it actually designed for working on Mars? Convection in the sodium heat pipes wouldn't work in zero G. > generate heat that is carried to the Stirling converters via passive sodium heat pipes. https://en.wikipedia.org/wiki/Kilopower

Convection still works in zero g, it's just driven by pressure gradients instead of density gradients.

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

#83

Post by DuskStar »

For those interested in learning more, I've found the Beyond NERVA blog to have really good articles! Their most recent post (and the 3rd in a series on Kilopower) [0] is on this set of tests, but there's also posts on more modern Nuclear Thermal Rocket designs [1] as you may have guessed from the blog's name.

[0] https://beyondnerva.wordpress.com/2018/05/02/krusty-we-have-... [1] https://beyondnerva.wordpress.com/2018/01/19/leu-ntp-part-tw...

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

#84

Post by InclinedPlane »

Sir_Substance wrote: post #16
dukoid wrote: post #13

Earlier quoted context omitted.

Wouldn't "passive decay" mean it's not based on fission -- but the article and video both mention fission...?

Passive decay is still fission, it's just not artificially sped up fission :) it's probably more complex than that. Is high speed natural decay of an artificially created or enriched heavy element natural or artificial? I'm not sure how that gets classified.

Decay is not fission. Some time fraction of decays may be spontaneous fissions but as a rule generally nobody calls decays fission reactions unless they are specifically mentioning spontaneous fission reactions.

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

#85

Post by DuskStar »

gnode wrote: post #48
mkoryak wrote: post #33

I wonder how safe these are. Could I get one in my basement and stop paying nstar for the rest of my life? Would my neighbors complain much?

They are not safe. They lack their own biological shield, and thus require the core section to be buried underground, as can be seen in various demo images. Even then, I suspect you wouldn't want to be too close while operating. They also lack other safety systems a commercial nuclear power station reactor has, having only a single control rod. This makes sense for an extraterrestrial reactor, as transporting mass to…

>They also lack other safety systems a commercial nuclear power station reactor has, having only a single control rod.

They also have a very strong negative thermal reactivity coefficient, meaning that as the reactor gets hotter it produces much less power. [0] From what I understand, with any reasonable amount of cooling this reactor won't melt down even with the control rod entirely removed, where "reasonable amount of cooling" means "not left to float in a vacuum with no radiators". (Also, if you remove the neutron reflector it'll stop working)

Granted, you'd probably want a bit more shielding before putting one in your basement. But it's not going to melt down.

[0] https://beyondnerva.files.wordpress.com/2018/05/full-power-t...

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

#86

Post by sigstoat »

Thorazul wrote: post #34

They should team up with Tesla to develop storage batteries for the reactors in case a reactor fails you would still have some temporary emergency power.

plenty of companies already make batteries for space applications. and the environment is demanding enough, the budget large enough, and the production volume low enough that more exotic battery chemistries are used. https://en.wikipedia.org/wiki/Batteries_in_space

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

#87

Post by godelski »

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 am guessing that you are talking about betavoltaics [1]. They were used to power pacemakers and are very useful for remote devices. They can't power much, but they are smaller than PV and don't have to be exposed to the sun (reflective).

Though there are larger devices that were used too.

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

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

#88

Post by godelski »

ajuc wrote: post #47

> For example, cutting off the system's cooling or ramping it up to its maximum level both resulted in a core temperature change of just 15 degrees or less. Why use cooling at all then?

Stirling engines drive because of a temperature differential. If you don't cool then those two temperatures will tend to equalize, becoming less efficient as the entire device warms up.

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

#89

Post by simcop2387 »

stcredzero wrote: post #54

I think someone should develop a 2 module design for this, where the Stirling engine is separated from the fission reactor with insulated pipes. Why? Weight savings. Insulated pipes can be made very efficient and relatively light. Radiation shielding can't easily be made light. By separating the modules into two sections, martian soil can be more easily used to provide the radiation shielding. It could even be built…

That might be a good second phase setup for a larger base, but this current one would be good for initial setup since it could be ready without having to produce anything on planet. That makes it good for rovers or other unmanned setups.

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

#90

Post by jcims »

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?
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