NASA demos little nuclear power plant to help find little green men NASA has announced successful tests of a small fission reactor capable of producing about 10 kilowatts of power, and hopes the technology will prove suitable for use on the Moon or Mars. The space agency’s developed the reactor because crewed missions will need lots more electricity than can be generated by either the Sun or …
NASA on Wednesday announced that a first round of tests - dubbed KRUSTY (Kilopower Reactor Using Stirling Technology) – have proven a success.
Their chief engineer added "Oy, after a my failure of a career in childrens television, it seemed pretty sensible to work at the local power plant for a few months, and brush up on my hobby of nuclear engineering, and this is what you get from that"
With apologies to....just everyone,
Steven R
No.
Unlike it's predecessor KRUSTY was designed to be started by (basically) pulling out the control rod and letting the heat pipes warm up to operating temperature, around 850c (which is cold by the standards of the nuclear fuel in PWRs)
And standing very well back of course.
It's the "Son of SL-1" to be used by American squaddies in space...
What could possibly go wrong....
"Ah wonder what'll happen when ah pull on this rod thing...".
I really wish though that they'd use sealed for life versions of these (or Thorium based ones) for small scale generation. 10kw is more than enough for the average house and combined with solar/wind would make for a much more flexible power network - and take the load off much more polluting gensets.
"am I misunderstanding how they work"
No, you're right. Heat rejection is a big problem for the moon. I don't know how deep you'd have to dig for a "lunathermal" solution, either. On earth it might be 20 feet or so, depending [then you just put a bunch of water piping undeground to reject heat into the earth]. On the moon you could do the same thing, but it's not very 'portable'.
I assume that the ginormous circular reflector is for that purpose. NASA knows how to make this work, as they did it on the space shuttle. But it's worth pointing out that any heat engine (including the Stirling engine) needs a differential temperature to work. So does a peltiere device, which is what I originally thought they'd use. But peltier devices aren't as efficient and would probably weigh more for kilowatt capable power.
I would also expect inverters and batteries to manage short-term transients. I can't see speed control on a Stirling engine being all that easy. If differential temperature drives it, then that's also what controls it [and you can't heat/cool things fast enough for speed control to work really well]. So they'd probably use 'load control' to also control speed, and use batteries as a 'surge' to keep speed within a safe band [with some safeties to burn off power or 'put on the brakes' when necessary].
In other words, controlling a Stirling engine generator could be like balancing a pole on your nose. Then again it might have some natural speed control built in, due to fluid friction and/or momentum, with that back/forth fluid motion thing going on.
It's a fair bet that the stirling engine + nuke plant would respond poorly to rapid transients, though. But the U.S. Navy solved this a long time ago in their own power polants, since you can go from "all stop" to "all ahead balls to the walls" in a reasonably short time on THOSE systems. Even so, electric power generation transients are usually a LOT slower than "flooring it" on a propulsion system. So maybe it's not an issue?
...10kw is more than enough for the average house and combined with solar/wind would make for a much more flexible power network ...
Since solar/wind is not reliable, you would need to have nuclear able to service the full power requirement.
That being the case, why would you want to turn nuclear off whenever the wind blew, and then turn it on again whenever it stopped? Turning things on and off is wasteful - as is creating two power generating systems when you only need one. Just use the nuclear, and save money by not buying high-maintenance wind turbines.
Nuclear fuel is VERY cheap and long-lasting, so there's little point in saving it....
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"https://en.wikipedia.org/wiki/Toshiba_4S"
I'm aware of these SMR (Small Modular Reactors) in progress, but to date none have been actually deployed. They would certainly be appealing for isolated locations (like islands) where obtaining generator fuel is an inherently expensive endeavor.
Sure. Put these little suckers in isolated corners of the world. What could possibly go wrong?
Supposedly, there are designs which stop the terraists getting their hands on naughty stuff. Such as this one. Using molten sodium as a coolant seems like a bad idea for devices you intend to put everywhere, but other than that it is supposed to be safe.
Of course, it could be a bit of a problem if we put those everywhere and then somebody figures out how to hack them to get them to churn out weapons-grade material. Or even just pull out the depleted uranium and disperse it as an ultra-fine powder with highly toxic, carcinogenic, teratogenic and mutagenic properties.
With a half-life of 4.5 billion years, U-238 needs to be disposed of in a way that it can never get into the environment. With such a long half-life the radioactivity isn't the biggest the problem, it's the toxicity, etc. Heavy-metal poisoning with a very heavy metal.
Alternatively, make bullets and artillery shells out of U-238. They're pyrophoric, so burn (fiercely) upon impact (and sometimes ignite on leaving the barrel) turning into ultra-fine particles of uranium oxide that rapidly disperse into the environment and contaminate it (and will continue to do so long after the sun swells into a red giant and engulfs the earth). Nobody would be stupid enough to do that, would they? Not even because its mass and hardness make it an ideal material for penetrating tanks (it's even self-sharpening, so it doesn't mushroom out as other compositions do). Not even because the pyrophoric properties mean that once it has penetrated a tank it incinerates the occupants, turning them into what is often called "crispy critters." And although it makes a good area-denial weapon targeting enemy forces and civilians alike (which makes it illegal) the particles are so fine they disperse in the atmosphere and end up contaminating the whole planet. It would be incredibly stupid to do that, which is why it's exactly what the US (and allies) have been doing in warfare for decades. Thousands of tonnes of the stuff by now.
As you said, what can possibly go wrong?
Quite true.
As this is the HEU (or "Bomb grade" as some wags like to call it) and was essentially available cheap to the programme as the US has been at a bit of a loss with what to do with all the cores they stripped out of the bombs from the last round of arms reduction talks.
Mines the jacket with "Special Ordnance" on the back.
"dynamically allocate current from different resources."
yes, including batteries, super-capacitors, flywheels, and other 'power storage' means, to absorb the surges while the individual power plants adjust themselves to the changes in demand.
You could even use a hydro-electric method that pumps water into a large storage area to absorb excess power, and then uses it to generate power when demand exceeds capacity. Just a thought at the moment. Its like the epitome of the whole concept.
I am pretty sure that "the power grid" (and the people running it) already uses fossil-burning plants and hydro-electric plants to handle demand changes (at least in the USA), while allowing nuke plants and solar/wind systems to run at full capacity as much as they can, then brings on 'peaker' plants to handle peak demands (gas turbines, diesel) when necessary. That assumes that GUMMINT didn't enviro-regulate everything to the point where no peaker plants were built... [so say hello to 'rolling blackouts' when it's cloudy and hot and humid and wind speed is low due to some kind of tropical depression, or whatever].
You don't turn off a reactor - you use a modded version of a solar/wind/mains/nuke charge controller/mains inverter to dynamically allocate current from different resources.
But that's why renewables are pointless. If you've got a 10kW heat engine, you just don't need solar or wind. Or the extra cost in both mass and money to get them into space. Or the extra risks due to a more complex design. Or the extra maintenance. Wind's useless in space, although some renewable junky would no doubt try flogging solar sails. On Mars, there's wind. Lots of it. And dust. Luckily the dust on Mars is weathered compared to the Moons, but would sandblast Martian installations.
NASA's solution's something that can be buried away, or shoved inside a suitable building. And any excess heat would be useful as well. Some solar could come in handy as a reserve source, and could then be cheaper/lighter.
Same would be true here on Earth. Mini-nukes + batteries and there'd be enough power for more homes than renewables can deliver on a cold, dark night. Sadly our politicians still can't seem to grasp this, despite having wasted billions on the renewables lobby.
If you've got a 10kW heat engine, you just don't need solar or wind. Or the extra cost in both mass and money to get them into space.
If you're planning on running a wind turbine in space, you have other concerns than just the mass of the equipment. Like transporting all the wind up to orbit to run it.
If you're planning on running a wind turbine in space, you have other concerns than just the mass of the equipment. Like transporting all the wind up to orbit to run it.
I think you missed this bit-
Wind's useless in space, although some renewable junky would no doubt try flogging solar sails.
But don't give the 'Renewables' lobby ideas. There's a perfectly good solar wind in space, and it's more consistent than down here. Which is why windmills are just as useless on Earth, where the terror is firmer, but the subsidy hose hasn't yet been turned off. So basically if you've got the prospect of reliable, predictable and dependable power from NASA's reactor, you don't need wind or solar.
"Nuclear fuel is VERY cheap and long-lasting, so there's little point in saving it...."
Funnily enough, not.
A nuclear reactor works by bunching the atoms together so their decay products bash into the next one, drastically increasing the natural rate of decay and hence also the heat output. Nuclear reactors last a few decades at most and even then they need the odd fuel change along the way. Damping it down with the moderating rod/s will extend its life considerably.
If you want a hundred-year-plus life from your radioactive gunk, then you have to keep it diluted and the wick turned waaay down - and the best way to pull energy from that is to use it in an ion engine.
Modern reactor designs have an expected life span of around 60 years and they're typically refueled every 1.5 to 2 years. Navel reactors use more highly enriched fuel and have much longer refuel periods, sometimes the life of the vessel.
New commercial power reactors are getting 50-60GWdays per ton of fuel.
"Nuclear fuel is VERY cheap and long-lasting, so there's little point in saving it...."
According to some estimates, the current quantity of spent nuclear fuel in storage around the world could be used to power thorium cycle reactors for around 25,000 years. And the thorium cycle consumes around 98% of the fuel compared to the 2%-3% maximum consumed in current reactor designs.
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It's the "Son of SL-1"
There are (unfortunately) a couple of significant similarities...
a) small, low power reactor that's portable
b) a single control rod can make it go critical
If there is a way of doing a safety shutdown that does not involve "that one control rod" it would certainly be a LOT safer This is because the fission products in a fission reactor are often "physically bigger" than the original material. Reason: higher density for uranium, lower density for "what it splits into". basic physics.
Basically, the fission process causes 'fuel swelling' as the fuel is burned off. This could cause 'blistering' and/or 'swelling' of the fuel material to an extent that it impedes control rod motion, depending on the design.
And that "single control rod" can EASILY get stuck as the fuel changes its shape over its lifetime. This means you lose control of the reactor. Oops.
To compensate for this, designers need to make sure that you have rod channels that resist the effects of swelling and blistering, as well as having "some other means" to shut the thing down.
NASA needs to work with the U.S. Navy on this (if they aren't already), as well as General Electric and Westinghouse and other military contractors that know how to build small reactors for submarines.
For a bunch of reasons, the reactor core needs to be very compact, as compact as possible. This not only reduces the fuel loading, but it improves the temperature coefficient. Small reactors tend to have negative temperature coefficients, which means that as temperature goes up, reactor power goes down. this makes it stable. Very large reactors tend to have positive temperature coefficients, which means you can't change power levels very fast, and have to constantly monitor it and tweek it to keep power levels stable, because an increase in temperature makes power go UP [in a transistor they call this 'thermal runaway']. Large reactors, however, can have a much larger fuel load so (in theory) you could go longer without refueling. Additionally, a large reactor could be fueled with 'fuel pellets' inside of a permanent tube structure, rather than alloyed fuel material that has to be completely changed out, making the refueling process a lot simpler.
So large reactors have their advantages. they're just WAY harder to control.
In this case the small reactor would be perfect. Down side, it would very likely have 'alloyed' fuel, meaning that it would be subject to swelling and blistering that could cause the single central control rod to stick, resulting in a potentially uncontrollable reaction. The end result could be a partial meltdown, but probably would just overheat everything and damage it beyond repair. Or, it might just slowly drop in temperature until it shuts itself down. There's no telling. Any of these are possible for a number of non-obvious reasons, caused by changes in power demand [among other things], and despite the highly negative temperature coefficient, it's still possible [following a large power transient] for a stuck rod to cause power levels to go unstable and either melt it down right away. or temporarily shut it down and make it go into a 'cyclic' uncontrolled shutdown/restart mode that results in an unrecoverable power transient that completely destroys the thing. Not 'boom', just melt.
So, yeah. That single control rod is a big concern.
It is sealed for life.
It's not designed to be taken apart or refueled (although being a single lump of metal with some holes in it "reprocessing" is pretty simple by nuclear standards).
The system uses negative feedback. The more power you take out the hotter it runs. The less you take out the slower it runs. That's without moving the control rod a cm.
Stick the control rod fully in it shuts down entirely. It's expected to be moveable within 1 week of full shut down.
No. It's designed to have the control rod in 2 positions. In or out.
Most of power tracking is done by the Stirlings pulling more or less heat from the system.
The team behind KRUSTY are very aware of the SL-1 situation and prompt criticallity issues.
So way worse that solar panels + ancillaries for orbit arround the earth.. but also way more compact and with less chances of being damaged my micrometeorites. Also depends way less on gyroscopes and reaction wheels + RCS, so less fuel needed.
I guess they will use this for deep space probes? like old RTGs ?
This is basically a very large RTG, but instead of using a thermocouple to generate electricity, it's using a Stirling engine, which is more efficient, but does involve moving parts.
I guess the fact that they can alter the rate of the fission reactions makes it more of a small reactor than the sources used in a typical RTG, but it's smaller than any 'real' reactor.
I guess it fills a useful niche between RTGs and a full size reactor.
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