Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

NASA to test prototype Kilopower nuclear reactor

world-nuclear-news.org

Post reply on HN
Print view View original

21–30 of 116 posts

Re: NASA to test prototype Kilopower nuclear reactor

#21

Post by yborg »

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 problem with Stirling engines is they have moving parts. It's highly unlikely a Stirling cycle generator on the Voyagers would have operated for 40+ years as their RTGs have.

Re: NASA to test prototype Kilopower nuclear reactor

#22

Post by curtis »

wolfram74 wrote: post #18
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.

> 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.

This is a good point. Here's a picture of a Plutonium-238 oxide pellet (referenced from [1]):

https://en.wikipedia.org/wiki/Plutonium-238#/media/File:Plut...

It will always look like that if you have no way to dump the heat -- basically it's a heat source which is always on.

On the other hand a nuclear reactor that's never been activated will have fuel that looks like this (referenced from [2]):

https://en.wikipedia.org/wiki/Uranium-235#/media/File:HEUran...

This is no doubt oversimplifying things, since Pu-238 is a pure alpha emitter, whereas once it's been activated, the fuel in a nuclear reactor will generate all sorts of nasty radioactive isotopes which in turn release alpha radiation, beta radiation, neutrons, and gamma rays. It will be pretty safe while it's still cold though -- in fact if it ends up in the ocean it's really unlikely to hurt anything, since there is already uranium dissolved in sea water.

[1] https://en.wikipedia.org/wiki/Plutonium_238

[2] https://en.wikipedia.org/wiki/Uranium-235

Re: NASA to test prototype Kilopower nuclear reactor

#23

Post by tpurves »

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…

For anyone else wondering why Pu-238 is dwindling, from the linked wikipedia:

“The United States stopped producing bulk Pu-238 with the closure of the Savannah River Site reactors in 1988.[12][13][14]

Since 1993, all of the Pu-238 used in American spacecraft has been purchased from Russia. In total, 16.5 kilograms (36 lb) has been purchased but Russia is no longer producing Pu-238 and their own supply is reportedly running low.[15][16]”

Interestinly, it looks like Canada (Ontario, Darlington) are starting set up operations to make some in the near future.

Re: NASA to test prototype Kilopower nuclear reactor

#24

Post by red75prime »

GlenTheMachine wrote: post #13
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.

Heat sink for space operation will be quite large though.

Re: NASA to test prototype Kilopower nuclear reactor

#25

Post by sp332 »

JumpCrisscross wrote: post #14
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.

It's because sometimes a rocket explodes on the launch pad or a few seconds later, and it could spread radiactive material over a very wide area.

Re: NASA to test prototype Kilopower nuclear reactor

#26

Post by ethbro »

sp332 wrote: post #25
JumpCrisscross wrote: post #14

Earlier quoted context omitted.

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

It's because sometimes a rocket explodes on the launch pad or a few seconds later, and it could spread radiactive material over a very wide area.

The alternatives still seem worse.

Re: NASA to test prototype Kilopower nuclear reactor

#27

Post by rwcarlsen »

sp332 wrote: post #25
JumpCrisscross wrote: post #14

Earlier quoted context omitted.

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

It's because sometimes a rocket explodes on the launch pad or a few seconds later, and it could spread radiactive material over a very wide area.

The half-life of fuel for these reactors is very long - over 100,000 years. So for all practical biological effects they are basically stable. If it exploded before it was activated (far into space), it would be about the same danger to people and the environment as the rest of the exploding metal the rocket was made of.

Re: NASA to test prototype Kilopower nuclear reactor

#30

Post by ChuckMcM »

Okay, this is awesome. 10kW is a serious enough amount of energy to do some fun stuff. Things like rovers that move at km/h rather than m/h and all day operation. It also solves the 'base load' problem on deep space missions which would like to use more power for radio communications.
Post reply on HN