NASA to test prototype Kilopower nuclear reactor(world-nuclear-news.org) |
NASA to test prototype Kilopower nuclear reactor(world-nuclear-news.org) |
[1] https://en.wikipedia.org/wiki/Stirling_radioisotope_generato...
“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.
http://www.planetary.org/multimedia/planetary-radio/show/201...
As an aside: There are some people who are very skeptical of both atoms and space exploration. I'm not sure what their motives are but given the amount of steel necessary to produce wind turbines, I'm unconvinced that "renewable" is actually "greener."
In light of the current geopolitical climate, it's probably better that NASA's (et al) plutonium should come from Canada vs. Russia.
The RTGs on both probes have decayed A fair amount at this point and are producing a lot less power.
10 years may seem short, but combined with an electrically powered thruster there is potential for doing types of missions we have not really been able to do before. That 10 years could be spent doing propulsion.
If you want to use it more in the science phase, use chemical rockets to get up to speed and then boot up the reactor in time to say, decelerate into orbit and you are looking at having the majority of that 10 years used at the destination.
My main concern isn't really the duration, but the reliability of the moving parts. But without plutonium, there are not a whole lot of other options for powering missions to Uranus and Neptune.
Still hard to imagine
https://en.wikipedia.org/wiki/Optoelectric_nuclear_battery
Its major, still undressed downsides are the requirement of expensive beta emitters, and synthetic diamond PV cells (everything else will die to beta particles)
You get around 15 years of useful work and 15% efficiency with current day technology.
It has no moving parts as RTG, has better power to weight than RTG, and has efficiency comparable to simple Stirling
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.
It think it's likely that the public relations nightmare NASA would have to go through to fly an actual reactor will be through the roof.
Not really, since "moving parts" ...
Is this actually a thermo-acoustic engine, or some other kind of sterling engine? Or are they equivalent? The article doesn't seem to mention "acoustic" (or an equivalent).
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...
I'll summarize some of the interesting points:
- The nuclear core (75kg of enriched uranium/molybdenum [1]) is designed to not go critical, even if it accidentally falls into the sea and is surrounded by water (which is a good neutron reflector). It only starts when you surround it with a neutron reflector made of beryllium (an even better neutron reflector, mainly due to less absorbtion). Combined with the fact that the reactor only gets nasty when it's been running for a while (and thus is already far away from earth) it is a lot safer than plutonium fueled RTGs.
- It would be very useful to reach far away destinations (like the orbit of Uranus, Neptun or Pluto) using ion drives, as they need to run for years and solar panels aren't effective far away from the sun.
- While there have been other attempts at developing nuclear reactors for space, most of them didn't go far. They could use an existing research reactor (Flattop [2]) for this project which already has all the required permissions to run, so a lot of paperwork could be saved for the Kilopower experiments.
- The Kilopower reactor is the first to use heatpipes instead of pumps for the heat transport and stirling engines for the energy generation. The first experiment was thus to show that the cyclic heat draw of the stirling engine would be safe, because usually nuclear reactors reach an equilibrium between heating up (and thus expanding slighty which slows down the reaction) and cooling down (which accelerates the reaction).
- Instead of the planned eight 125W Stirling engines, they're currently using two 70W ones from the Advanced Stirling Converter Project [3]. The other ones will be simulated using simple heatsinks.
- Theoretically it could run for hundreds of years (after 500 years less than 1% of the uranium will be used), but the Stirling engines will break much sooner than that.
[1] http://www.iaea.org/inis/collection/NCLCollectionStore/_Publ...
[2] https://en.wikipedia.org/wiki/Flattop_(critical_assembly)
[3] https://tec.grc.nasa.gov/rps/stirling-research-lab/advanced-...
So a bit OT, I was wondering if anyone has yet thought about the solution of still using solar panels for them, but to also use a mirror to focus more light in the direction of the probe or a laserbeam?
I mean, theoretical I don't see why not, appart from being more expensive? Andd you could also offset the laser/mirror cost, because you only need them later on ....
(but to be on the safer side, I still would add a RTG)
Say you have a mission to Uranus, you will need a mirror with 400 times the area of the solar cells to get as much power as they would in earth orbit.
Dibs on Solar Harvester
But if you use a laser?
I imagine it will be easier to focus it more precisely?
2-5 W / kg.
Solar cells seem to be about 150 W/kg.
This is relevant for outer system exploration (beyond Jupiter) or maybe for night power on planetary / moon surfaces.
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/201700...
But apparently the 10 kW is modeled to weigh about 1800 kg, so no need to worry about one in a car any time soon.
Also, you need more than a few kilowatts to power a car. 10kW = 13.4 hp. It may work, but you won't break speed records...
Kilopower is safer, because it would launch inert, and it avoids Pu so any failures would be less toxic.
Downplaying the usefulness of a technology because of imaginary protesters isn't very helpful.
I agree with the sentiment. Anti-science sentiments proliferate partly because science doesn't spend much on public outreach, especially compared to people who want to make a buck off scaring others about new technologies. NASA has been doing more and more PR work over the past few years, and that's great - but IMO in this case, they really need to get someone who looks and sounds confident, and who would go on national TV and say "Yes, we are totally sending a nuclear reactor to space, why wouldn't we?".
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").
The space electricity tanker idea is theoretically possible, but might not make any economical sense. For it to be worth it, it would have to store a lot of energy, so that it could ship back more than the cost of moving it around, while also being competitive with simply building more bigger collectors further away (and closer to the industry). But maybe a highly eccentric orbit, with a very low perihelion, would work.
Not totally sure if the math works out on this, but I could see moving the energy-intensive industry closer to the Sun, and having it use beamed energy to move resources and products to itself and back.
(Not many, but more than zero.)
Not that I'm disagreeing with you really - mechanical devices have high failure rates. 10 years maintenance-free is a bit of a dream. As a mechanical engineer I'm interested to see whether the Stirling engines involved have radically different scaling to optimise for reliability, or NASA just plan to do the engineering really well.
Of course manned maintenance may be possible - they are touting this technology for Mars bases. Plus robotic maintenance is going to become more of a thing over time.
Note that while implementations usually show a crank and rod with a flywheel, it could just as easily use a magnet and coil to generate electricity.
That get's you down to a single part.
Then you have this:
https://en.wikipedia.org/wiki/Thermoacoustic_heat_engine
...that gets you down to something that can generate sound from a heat differential, and you could couple that sound to some kind of transducer to generate electricity. Still a moving part, though.
You probably can't get zero moving parts and yet have it do useful work, but you can get really close I think.
As a heuristic, the less mechanical parts in any system, the more efficient it is over time.
Ideally, everything that's built is engineered like a spacecraft, because to some extent it is, and is onboard one.
There must be some way to directly turn radioactivity (or heat) into thrust with sufficiently high exhaust velocity!?
As far as the 3kW kettle is concerned having a battery to provide for these surges is entirely viable.
That's probably the biggest issue for deep space it's extremely difficult to shed heat in hard vacuum (without ejecting mass and its heat with it) as you can only radiate it away.
Beyond that, Steel is 100% recyclable^, and that accounts for over 65% of US steel production. Recycled steel can be done in arc furnaces, requiring no coal coke. [1]
Info like this is at the tip of your fingers.
[0] https://www.worldsteel.org/en/dam/jcr:f07b864c-908e-4229-9f9...
[1] https://seekingalpha.com/article/3785906-metallurgical-coal-...
^ This rate is never achieved. Global average is ~90%, as some countries aren't efficient: http://www.steel.org/sustainability/steel-recycling.aspx
Downvote me if you like but our fuel mix in this country is still ~40% combustion and the calculations on wind power say that at current power requirements civilization will harvest enough energy from the air currents to change the climate again. Maybe it stops hurricanes, I have no idea.
Also, steel, like atomic fuel, is toxic to produce and reprocess!
I know it is much-despised by but I am curious as to the lifetime energy footprint of a fission reactor facility with onsite fuel-reprocessing and waste transmutation. And then? Tokamak. Won't even need a turbine!!
Parts of that system don't even exist yet but me I believe one day there will be clean atoms, fission or fusion, and they will require even less energy to produce and maintain than the wind and solar grid.
But then, I have lived among the fission reactors my entire life. Perhaps I am "mad from the rads" ;)
?
Wind doesn't circulate through the atmosphere forever with perfect efficiency, it eventually dumps its energy into the ground via friction.
There's no difference between slowing wind down with a wind turbine and slowing it down with a tree, they both end up as heat eventually.
Voyager 1 is going for 50 years ...
We can examine this limit in the context of delivering energy to a remote object. This analysis will be simple - we assume that the optics are perfectly aligned (dubious - pointing is difficult); we assume nothing about the absorption properties of the object, which will necessarily need to be very high efficiency. The angular size T of a laser beam of wavelength L emitted by an aperture of diameter D_a is roughly L/D_a. Similarly, using the small angle approximation, this angular size T at the object itself will be the width of the beam, W, divided by the distance between the object and the aperture, D_o: T = W/D_o. Ultimately, this gives us the width: W = L*(D_o/D_a).
What does this tell us about the practicality of such a system? Visible light, wavelength roughly 500 nm, is perhaps a solid guess for a real system. Realistically the aperture size is probably limited to about 10 meters, but we can go even further and assume a synthesized aperture of a realistic system being 100 meters. You would want to get all of your beam for power transmission, so lets assume an upper limit for the beam width at the object to be 100 meters as well - probably unrealistic, but maybe solar sail/ultralight absorbers could get there. Throwing these numbers in gives a maximum range of... 2x10^10 meters. This is roughly a tenth of an AU. In comparison, this is about 50 Earth-Moon distances... and only a quarter of the distance between Earth and Mars at their closest approach. Coincidentally, this is also about one light-minute.
Any real power delivery system, using current tech and without assuming convenient fictions, will have a much more limited range. In short, lasers are not really perfect rays, even though they are approximately so over scales we typically encounter; at astronomical scale, diffraction always wins. This is why it is usually way better to bring the power with you - especially as you lose solar irradiance as you get further from the Sun. And for bringing power with you, nothing beats nuclear for energy density.
(also memorys of phsyik lectures are coming up again)
And forgive a nonserious reply:
"And for bringing power with you, nothing beats nuclear for energy density"
I think fusion does ...
anyway, yes sure fusion is nuclear power, I just read in your comment nuclear fission which you did not wrote ... so never mind I am just tired at some airport ...
The way I feel it, engaging with irrationality legitimizes it. You don't want to do that too much. If you bend over yourself to explain that people really don't need to worry, it'll only make them feel that there is something to fear.
What I want to suggest is engaging with people on an emotional level, but projecting confidence while doing so.
Nuclear energy may be safe, if done under near-perfect condition, with extremely large budgets to understand risks, and plans to mitigate incidents. There is truth to the argument that nuclear power saves lives compared to coal power.
But nuclear power isn't inherently safe. It is, by its very nature, extremely dangerous. Actual nuclear scientists understand that. See, for example, Feynman's work on nuclear safety during the Manhattan project.
Strapping a nuclear reactor to a rocket is almost by definition a dirty bomb. Depending on the height and mode of an eventual launch failure, the result could be anything from Tchernobyl to a less-dramatic yet more deadly dispersal of nuclear material in the upper atmosphere.
The dose-response relationship of radiation exposure is largely linear, meaning the latter event might just increase your risk of brain cancer by 0.005%. Yes, you may consider it negligible. But statistically, it would kill half a million people.
To blithely state that "nuclear is safe, hoho, why shouldn't we strap Plutonium to a rocket, you environmental nincompoops" has nothing to do with science, and gives science a bad name. Maybe NASA could come up with a way to protect a reactor during a missile launch. But it wouldn't be easy, and saying "why wouldn't we?" on TV would not inspire confidence in their abilities, but doubts in their sanity. The right thing to say on TV is "We're sending a reactor into space, and here are the mechanisms we've come up with to make it safe..."
But maybe I should have stated my main assumption explicitly: people at NASA know what they're doing. They're not incompetent morons, they can do the math. They already have absurd amounts of procedures in place to ensure a launch failure doesn't hurt anyone. They're not just trying to strap a bunch of random nuclear isotopes on a rocket and hope for the best.
> Strapping a nuclear reactor to a rocket is almost by definition a dirty bomb.
No, it isn't. A dirty bomb is meant to create a large-scale radioactive contamination that's dangerous to humans, and U-235 is probably the last thing you'd like to put in it. It's an alpha emitter with a half-life so long it doesn't matter, so the only effect you'd get is heavy metal poisoning.
(That's beyond the fact that dirty bombs are speculative devices, and from what I read, they actually turned out not to be a real issue in practice.)
> Depending on the height and mode of an eventual launch failure, the result could be anything from Tchernobyl to a less-dramatic yet more deadly dispersal of nuclear material in the upper atmosphere.
That's the kind of thinking that I suggest we need to fight with a serious public outreach effort. Chernobyl was a total clusterfuck, but the only connection between it and the NASA project is the word "nuclear" in newspaper headlines. Chernobyl was an active reactor, and its explosion contaminated the area with reaction products that had very low half-life and underwent beta and gamma decay, making them really dangerous, unlike plain U-235.
> To blithely state that "nuclear is safe, hoho, why shouldn't we strap Plutonium to a rocket, you environmental nincompoops" has nothing to do with science, and gives science a bad name.
I'm not saying that. I'm saying that there's so much baseless fear around nuclear energy as a whole, that it's high time we stopped treating it as reasonable. And right now, the biggest danger around nuclear energy is the cost in lives of it not being used instead of fossil fuels.
The thing about this reactor is that it doesn't work until you switch it on - so in case of an explosion you are spreading a near-stable isotope that you could handle without any health risks. Chernobyl doesn't compare, because the ashes were spreading isotopes produced as a result of operating the reactor, and are simply not present here until the reactor is actually switched on.
Consider coal electricity. It kills much more people globally than potential harm from space probes with nuclear engine blowing up in atmosphere periodically. Yet we continue to burn coal.
Or consider bio-engineering. We mess with cells without understand how they work. And since cells are self-replicating, we have a potential of quickly making the whole planet permanently unsuitable for human life. Compared with that the total risk of nuclear is bounded even after accounting for a possibility of a large-scale global nuclear war. Yet protests against, say, GMO are rather weak compared with protests against nuclear energy.
[1] http://www.wipp.energy.gov/WIPPCommunityRelations/images/pho...
However, containment vessels like that are usually for refined ores, which end up in reactors, smoke detectors, medical devices, radiotherapy machines, you name it. Too expensive and possibly hazardous to airlift.
As far as I know, production of atomic weapons has stopped in this country and we're not even sure if they still work (half-lives--they rot). Could've been materiel for a stewardship program at the Hanford Site, or waste being evacuated from the Hanford Site.
Generally speaking, the remaining atoms transported and transmuted are for peace. That's why Russia brokers Uranium to the States, and why people in Kazakhstan and elsewhere continue to mine fissile ore.
If you were to shut down the remaining fission plants of Planet Earth, civilization as we know it, would end almost immediately, such is our need for these fuels. It would not be pretty--consider the amount of electric heat, the number of electric stoves with 50+ year duty lifetimes. That's why Japan recycles spent fuel at the French reactor.