NASA completes full-power tests of small, portable nuclear reactor • Hacker News Board

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

#51

Post by lightbyte » Thu, May 03, 2018, 5:58 PM UTC

monocasa wrote: post #50

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?

When a rocket explodes, it's normally in the atmosphere right over an ocean.

I misunderstood what you were saying than, I thought you meant the rocket was exploding when it was already far into space away from Earth.

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

#52

Post by noir_lord » Thu, May 03, 2018, 6:00 PM UTC

lightbyte wrote: post #49

HappyRobot wrote: post #5

Earlier quoted context omitted.

I think the drawback for space disposal is the risk of rocket failure. If a rocket explodes with nuclear waste on board, the waste would spread over a large area. It's safer at the moment to consolidate nuclear waste in small areas away from civilization.

>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?

If it blows up 500m above the launch pad you aren't in space.

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

#53

Post by diggan » Thu, May 03, 2018, 6:00 PM UTC

lightbyte wrote: post #49

HappyRobot wrote: post #5

Earlier quoted context omitted.

I think the drawback for space disposal is the risk of rocket failure. If a rocket explodes with nuclear waste on board, the waste would spread over a large area. It's safer at the moment to consolidate nuclear waste in small areas away from civilization.

>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?

Think what the argument against it is that the rocket explodes during launch, before actually leaving earth behind. Then it would most probably be noticeable.

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

#54

Post by stcredzero » Thu, May 03, 2018, 6:01 PM UTC

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 out of bricks, which we already know can be made out of martian soil.

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

#55

Post by jjoonathan » Thu, May 03, 2018, 6:09 PM UTC

JTbane wrote: post #24

Pretty amazing that the simple Stirling engine can be the best choice for generating kilowatts of power in a hostile environment.

The magic comes from the nuclear half, not the Stirling half.

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

#56

Post by Symmetry » Thu, May 03, 2018, 6:16 PM UTC

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?

You can't extract energy from a heat engine without cooling. Useful work is done in the process of moving thermal energy from a high temperature location to a low temperature location.

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

#57

Post by rfrey » Thu, May 03, 2018, 6:24 PM UTC

telchar wrote: post #15

cathhhhji wrote: post #11

Earlier quoted context omitted.

Stirling engines are not efficient. Using that heat to make steam to turn a turbine is much more efficient. But it would be harder to make that portable.

Yes they are. An ideal stirling engine has the Carnot level efficiency, i.e. maximum theoretical efficiency for a heat engine. https://blog.mide.com/thermodynamic-theory-of-the-ideal-stir...

You may be interested in reading Allan Organ’s books. He claims that aspirations to Carnot efficiency are a red herring and claims (with Much Math) that the peak efficiency is closer to 50% of The Carnot cycle.

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

#58

Post by baybal2 » Thu, May 03, 2018, 6:26 PM UTC

ttul wrote: post #25

cathhhhji wrote: post #11

Earlier quoted context omitted.

Stirling engines are not efficient. Using that heat to make steam to turn a turbine is much more efficient. But it would be harder to make that portable.

Hmm. Why not talk to Etalim: https://www.etalim.com/ They invented and are very close to commercializing a direct heat-to-electricity converter that uses acoustic waves. No moving parts. Close to 30% efficiency.

It is effectively another stirling, just with membrane instead of piston, and very high frequency of operation.

Sound == heat.

An AMTEC converter may be an another "fully self-contained" solution

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

#59

Post by baybal2 » Thu, May 03, 2018, 6:34 PM UTC

I wonder, can you make a stirling with plutonium pentafluoride working fluid? Eg, cold chamber with neutron poison, hot chamber out of a neutron moderator material?

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

#60

Post by ChuckMcM » Thu, May 03, 2018, 6:40 PM UTC

They nailed all their milestones. This is tremendously important work with regards to a future outpost anywhere and possible outposts on Earth. (Imagine how much fuel you wouldn't have to ferry down to Antartica each year to prepare for winter operations, for example).

Now to ruggedize the heck out of it and make it easily transportable.