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NASA to test prototype Kilopower nuclear reactor

world-nuclear-news.org

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Re: NASA to test prototype Kilopower nuclear reactor

#11

Post by jessriedel »

nickhalfasleep wrote: post #4
jessriedel wrote: post #3

Earlier quoted context omitted.

What's the advantage over direct thermoelectric conversion?

An RTG uses the Seebeck effect, which gets you microvolts per degree kelvin. A Stirling engine can theoretically extract many times more energy from the same temperature differential, but with a larger complexity.

Actually, when I mentioned thermoelectric conversion I wasn't referring to an RTG (which is just nuclear decay) but rather to the true nuclear reactors that the Soviets put in space:

https://en.wikipedia.org/wiki/Romashka_reactor https://en.wikipedia.org/wiki/TOPAZ_nuclear_reactor

They used thermoelectric conversion rather than a Sterling engine with moving parts (although I guess TOPAZ is technically "thermionc coversion").

Re: NASA to test prototype Kilopower nuclear reactor

#12

Post by jessriedel »

curtis wrote: post #5
jessriedel wrote: post #3

Earlier quoted context omitted.

What's the advantage over direct thermoelectric conversion?

> What's the advantage over direct thermoelectric conversion? Stirling engines can approach 50% efficiency [1], whereas thermocouples are usually less than 10% [2]. [1] https://en.wikipedia.org/wiki/Stirling_engine [2] https://en.wikipedia.org/wiki/Thermoelectric_generator#Effic...

Cool, thanks! It's really surprising to me that inserting a mechanical intermediary has such a large efficiency advantage.

Re: NASA to test prototype Kilopower nuclear reactor

#13

Post by GlenTheMachine »

giarc wrote: post #9

Anyone know the approximate size of that thing? Hard to tell from the picture.

Hard to tell what the weight is, of course. Judging from the size of other objects in the picture (the lift point and the connectors) it's very roughly around four cubic feet. Which is actually pretty awesome; the equivalent solar panels would be significantly larger.

Re: NASA to test prototype Kilopower nuclear reactor

#14

Post by JumpCrisscross »

GlenTheMachine wrote: post #8

This is a very cool technology, but frankly I have a hard time imagining that it will see much use. NASA sees public protests and scare mongering whenever it tries to fly an RTG, which is based in the radioactive decay of (usually) plutonium, and does not use a nuclear chain reaction. They did fly one on Mars Science Lab, because it was the only way to get enough power for the rover. But it takes a PR hit every time…

Has anyone studied these protesters? My off-the-cuff sense is they’re mostly older environmentalists.

Re: NASA to test prototype Kilopower nuclear reactor

#15

Post by maxxxxx »

GlenTheMachine wrote: post #8

This is a very cool technology, but frankly I have a hard time imagining that it will see much use. NASA sees public protests and scare mongering whenever it tries to fly an RTG, which is based in the radioactive decay of (usually) plutonium, and does not use a nuclear chain reaction. They did fly one on Mars Science Lab, because it was the only way to get enough power for the rover. But it takes a PR hit every time…

"RTGs are therefore only used when no other technology will work."

I think this is a good thing. And it seems they can use them if nothing else works.

Re: NASA to test prototype Kilopower nuclear reactor

#16

Post by dgoodell »

giarc wrote: post #9

Anyone know the approximate size of that thing? Hard to tell from the picture.

I saw a full scale prototype/model in the Stirling lab. I think a strong person could have lifted it up. It’s just several lbs of uranium with several heat pipes coming out of it connected to Stirling engines. I don’t think they have enough actual Stirling engines because the ASRG project to make them was cancelled so I think they use simulators for the heat load.

Re: NASA to test prototype Kilopower nuclear reactor

#17

Post by gozur88 »

curtis wrote: post #6

This is similar to the "Stirling radioisotope generator" [1] but it is an actual nuclear reactor (albeit a small one). Both systems are a response to the same fundamental problem, the dwindling supply of Plutonium-238 [2]. The Stirling radioisotope generator uses Pu-238 more efficiently than thermoelectric RTGs, and the nuclear reactor from the article dispenses with Pu-238 altogether. [1] https://en.wikipedia.org/wi…

The other problem with RTGs is they scale very badly.

Re: NASA to test prototype Kilopower nuclear reactor

#18

Post by wolfram74 »

curtis wrote: post #6

This is similar to the "Stirling radioisotope generator" [1] but it is an actual nuclear reactor (albeit a small one). Both systems are a response to the same fundamental problem, the dwindling supply of Plutonium-238 [2]. The Stirling radioisotope generator uses Pu-238 more efficiently than thermoelectric RTGs, and the nuclear reactor from the article dispenses with Pu-238 altogether. [1] https://en.wikipedia.org/wi…

Also it is my understanding that /because/ it dispenses with the plutonium out right it's more benign until you turn it on. Which you would presumably do after the potential for RUD in atmosphere has diminished considerably.

Re: NASA to test prototype Kilopower nuclear reactor

#19

Post by nine_k »

maxxxxx wrote: post #15
GlenTheMachine wrote: post #8

This is a very cool technology, but frankly I have a hard time imagining that it will see much use. NASA sees public protests and scare mongering whenever it tries to fly an RTG, which is based in the radioactive decay of (usually) plutonium, and does not use a nuclear chain reaction. They did fly one on Mars Science Lab, because it was the only way to get enough power for the rover. But it takes a PR hit every time…

"RTGs are therefore only used when no other technology will work." I think this is a good thing. And it seems they can use them if nothing else works.

"Good" as in "extra expense and possibly lesser capabilities", I suppose.

Re: NASA to test prototype Kilopower nuclear reactor

#20

Post by brians »

jessriedel wrote: post #12
curtis wrote: post #5

Earlier quoted context omitted.

> What's the advantage over direct thermoelectric conversion? Stirling engines can approach 50% efficiency [1], whereas thermocouples are usually less than 10% [2]. [1] https://en.wikipedia.org/wiki/Stirling_engine [2] https://en.wikipedia.org/wiki/Thermoelectric_generator#Effic...

Cool, thanks! It's really surprising to me that inserting a mechanical intermediary has such a large efficiency advantage.

Why does mechanical stuff suck? Because of friction of moving parts. Too much energy is lost to heat. For a thermal engine, if you can arrange to put the moving parts mostly on the hot side, that’s no longer loss.
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