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DARPA wants to bypass the thermal middleman in nuclear power systems
- xhkkffbf 2y agoIf photovoltaic cells can create power from radiation in the visible light range, I suppose there might be radiovoltaics that can do something similar. But I wonder if they can capture the high power fluxes from a modern core.
- actionfromafar 2y agoMayne one could run it in the visible range, or almost there. Wasn’t there some new kind of IR solar cells?
- ta988 2y agoYou have to go the other way of the spectrum toward something that loves to avoid interacting with matter...
- baking 2y agoI think the issue is the low absorption rate. Eli Yablonovitch proposed a box of PV cells facing inward containing a heat source where the IR light would bounce around until converted to electricity or absorbed as heat. This could be used inside a water heater so waste heat could be stored. Known as thermo-photovoltaics. See this talk I think: https://www.youtube.com/watch?v=lDxJsa8miNQ https://www.youtube.com/watch?v=lDxJsa8miNQ
- fulafel 2y agoWe just need some blimp attached mini suns floating in the sky in the night and this can power all the existing solar panels on the ground.
- geuis 2y agoHelion https://www.helionenergy.com/technology/ https://www.helionenergy.com/technology/ is a commercial fusion company working on a design that theoretically would use direct energy capture from the magnetic fields generated during the fusion event. They made some headlines last year. Not clear if their approach will be successful but it certainly is an interesting approach.
- TheRealPomax 2y agoCommercial energy company. Not fusion company. There are no fusion companies on this planet yet.
- ChrisClark 2y agoWhat do they plan on using to generate energy then, oil, coal, solar, wind? Something else?
- TheRealPomax 2y agoSo far: looks like hope and promises rather than any of those.
- Intralexical 2y agoThey claim to have performed fusion, but not yet produced net energy. So they're very much a fusion company, but not an energy company: > In 2023, we will end operations on Trenta, our 6th fusion prototype… Our results suggest that Trenta is currently the best performing privately-funded fusion machine in the world. After these last weeks of plasma operations under vacuum, we will retire Trenta and move all focus to Polaris, our 7th fusion prototype, expected to demonstrate net electricity in 2024. So, they have 143 days left to make good on their current timeline, I guess.
- TheRealPomax 2y agoThey're an energy company that has failed to produce any yet because of how they chose to generate that energy. Unfortunately, like everyone else who tried this so far, they can make tiny bang go flash, and that's unfortunately still just about it. So, indeed, so far they failed at energy, and they've only succeeded at fusion in the same way and at the same scale that university labs have. So I guess you're right: they're not even any kind of company at the moment. They don't sell anything. They're an R&D lab.
- Animats 2y agoNuclear batteries with beta emitters driving some kind of semiconductor have been around for a while, but they're very low power.[1] "... Betavolt's team of scientists developed a unique single-crystal diamond semiconductor that is only 10 microns thick, placing a 2-micron-thick nickel-63 sheet between two diamond semiconductor converters to convert the decay energy of the radioactive source into electric current to form an independent unit." "... 100 microwatts, a voltage of 3V, and a volume of 15 X 15 X 5 cubic millimeters ..." 3-4 orders below the power requirements for a phone. An AirTag-type intermittent device, though... So, can those be scaled up? Are all those little beta-emitters in coin cell form factor going to be a problem? Nickel-63 has a half life of 100 years, so they'll be active for a while. Not dangerous unless broken up and ingested, but need to be kept out of the food chain. [1] https://www-betavolt-tech.translate.goog/359485-359485_645066.html?_x_tr_sl=auto&_x_tr_tl=en&_x_tr_hl=en&_x_tr_pto=wapp https://www-betavolt-tech.translate.goog/359485-359485_64506...
- saulrh 2y agoNot dangerous unless broken up and ingested, but need to be kept out of the food chain. No worse than a NiCad in that respect. Probably better, if anything, since it's so much easier to detect and track.
- giantg2 2y agoAnd set off all the NBC detectors on the highways near major cities.
- arcticbull 2y agoWell yes but only if destroyed. Then wouldn’t you call that a feature? When in their enclosures there should be no radiation.
- giantg2 2y agoNo way could all the alerts be tracked.
- wizardforhire 2y agoI always thought super conducting ccds with plasma scintillating cell intermediaries were the way to go. Capture the alpha and beta radiation with the plasma scintillators. Plasma being ideal because it wont degrade with bombardment. Capture the em radiation with ccds. We normally think of ccds as low power capture devices for cameras. Theres no reason they couldn't be scaled up to handle the power requirements. Perfect use case for super conductors. This of course for moderate to large scale fusion reactors where cost is a negligible object. Of course the dream is solid state Hau arrays. Which Dr Lene Hau postulated 15 years ago… but thats a whole other story.
- wizardforhire 2y agoOf course plasma will degrade its just easier to separate out the products. You could feed the plasma back into the reactor and use cyclotron resonance. Alpha and Beta decay being one of the big problems with reactor design as the walls degrade over time. So designing for that with an active system seems to me to be a way a viable solution to minimize maintenance.
- carabiner 2y agoCould this cause a resonance cascade?
- wizardforhire 2y agoUnlikely as resonance in this case is referring the minuscule difference in mass between isotopes which results in preferential orbits within a tokamak which can be exploited for separation. I guess depending on what you're separating and whether or not someone is paying attention I guess conceivably a runaway event could occur but I think the masses and densities involved are too small to be of any concern.
- epistasis 2y agoThis is pretty much the only hope for nuclear power in the future. Current reactors are way too expensive, and they do not get cheaper the more we build of them. Miles upon miles of pipes with high-performance welds meant to last decades is no way to build a cheap and cost-effective electrical generation system. We need something better. Also, getting off a thermodynamic heat engine means the chance for far greater efficiency. Going through a heat cycle is hugely inefficient. For example, just extending the lifetime of the Diablo Canyon reactor pair in California, for five years extra life from 2025 to 2030, is expected to cost a minimum of $8.3B. That's the utility's claim before the work has been done, and life all nuclear/construction projects, it will almost certainly balloon midway. TL;DR nuclear needs a tech breakthrough like direct conversion.
- cinntaile 2y agoIf they utilize the waste heat for eg. district heating, the equation looks a lot better. Unfortunately most cities don't have district heating.
- pfdietz 2y agoThere are already lots of sources of low grade waste heat. Since we aren't exploiting them, it must not be worth doing. So, for nuclear district heating, you'd need higher quality heat, probably steam.
- cinntaile 2y agoYou don't use steam for district heating. There are two problems here, the first one is that district heating doesn't exist in a lot of places so the infrastructure needs to be built. The second problem is that people are afraid of nuclear so running water through their house warmed almost directly with nuclear heat is a sensitive topic. It's not actually dangerous of course, but perception matters. Actually there is a third reason now that I think of it. Nuclear plants are usually not close to big enough cities to absorb that heat, but it's possible to transport the water over 100km while still retaining enough heat for district heating.
- at_a_remove 2y agoThis is one of the reasons why, as an undergrad, I switched from nuclear engineering to physics: at the end of the day, we're still using heat and turbines, just with extra, more dangerous steps; although the materials engineering aspect is recognizably challenging, I found it not particularly thrilling. At other, far end of the scale, if Hawking radiation does exist, black holes could be considered converters of mass to energy, skipping all of the conservation of baryon and lepton numbers ... although at very large timescales until you have a fizzy, spicy nano black hole on hand. Controlled capture of the various types of radiation (sometimes I find that word to be sloppy) to extract the kinetic energies does not seem to be physically impossible, but I have oft wondered how as I think about various nuclear batteries which have existed. Indeed, the article doesn't even break it down enough: beta ought to be split into beta-plus (positrons) and beta-minus (electrons), and they skipped some 2p emissions. My guess is that not only will each need its own approach, but that each of those would be subdivided into different energy bands, not unlike having different compounds for chlorophyll-A and chlorophyll-B, only for, say, fast neutrons versus thermal neutrons. And I think that's gonna be materials engineering again. Whoops!
- mmooss 2y ago[dead]
- mannykannot 2y agoIn fission, it seems that most of the energy release is in the form of the kinetic energy of the daughter nuclei rather than gamma radiation or the kinetic energy of neutrons (from Wikipedia: For uranium-235 (total mean fission energy 202.79 MeV), typically ~169 MeV appears as the kinetic energy of the daughter nuclei, which fly apart at about 3% of the speed of light, due to Coulomb repulsion. Also, an average of 2.5 neutrons are emitted, with a mean kinetic energy per neutron of ~2 MeV (total of 4.8 MeV.) The fission reaction also releases ~7 MeV in prompt gamma ray photons.)[1] Given this, I'm guessing that, for direct conversion to be at all efficient here, a significant fraction of this energy would have to be converted into electrical potential energy rather than be dissipated as heat in collisions between these nuclei and any part of the apparatus. Are there any nascent technologies of this sort? [1] https://en.wikipedia.org/wiki/Nuclear_fission https://en.wikipedia.org/wiki/Nuclear_fission
- db48x 2y agoIt’s been proposed as an extremely efficient spaceship drive. Make 1µm beads of fissile fuel embedded at below critical density in aerogel. A thin sheet of aerogel with these fuel pellets in it is then inserted into the engine right inside a very strong magnetic field. Bombard the fuel with neutrons to ramp up the fission rate and those same daughter nuclei come streaming out of the pellets. They are still charged, so in the magnetic field they take a curved path. They push the magnet forward as the field pushes them out the back of the engine. With an exhaust velocity of 3% of the speed of light, they can get enough ΔV out of a few kilograms of fuel to zip out to Pluto and back in a few years.
- drivebyhooting 2y agoThat sounds very cool. Like a nuclear ion drive. Is there a technical paper about it?
- Intralexical 2y agoSounds like what Wikipedia calls a "Fission-fragment rocket", I think? So check the citations for papers: https://en.wikipedia.org/wiki/Fission-fragment_rocket https://en.wikipedia.org/wiki/Fission-fragment_rocket
- analog31 2y agoThis is just a speculation. What if we were to use the heat from fission to generate hydrogen instead of electricity? Would that help at all? For instance a high enough temperature will cause water to dissociate.
- geuis 2y agoAs far as I know (and its not very far to be fair), the main way to generate hydrogen would be via electrolysis in water, which requires electricity. Which means you have to turn that heat into electricity first anyway. This is one of the big critiques of using hydrogen as an everyday fuel source. Takes more energy to produce that you can recover. Its super hard to store (requires very cold temps, or high pressure), and it has a habit of wiggling through any other material's atomic bonds and overall weakening the container material. But if there is another chemical method that used thermal energy in the process to produce hydrogen then there might be some possibilities in the idea.
- rgmerk 2y agoThere's been some research into high-temperature electrolysis. The idea is that a lot of the energy to split the hydrogen and oxygen can be provided as heat; that means you need a lot less electrical energy. To a rough approximation, for every three units of heat energy produced by a nuclear plant, you get one unit of electricity, so the process could in theory considerably reduce the cost of zero-carbon hydrogen. In practice, it seems like it's going to be very hard for a nuclear plant to beat an electrolyser that runs when near-free solar electricity is available. As you say, if you get hot enough you can do away with electrolysis entirely. A little bit of casual reading suggests that the temperatures required by a naive approach are in excess of 2000 degrees Celsius, far, far beyond the point where any existing or near-term reactor design would turn into a puddle of very radioactive molten metal.
- g15jv2dp 2y agoAnd then what do you do with the hydrogen? Unless you plan on fueling your spaceship with it, you must burn it off to harvest the thermal energy... I'm sure you see the issue here.
- orbital-decay 2y agoOne of the previous attempts at that, with a "power density of a gasoline tank", according to the authors: https://en.wikipedia.org/wiki/Optoelectric_nuclear_battery https://en.wikipedia.org/wiki/Optoelectric_nuclear_battery
- elevaet 2y agoWhat's the typical efficiency of a nuclear power plant? i.e. what fraction of the energy from the fission reaction gets converted into electricity?
- Muromec 2y agoI remember something like 1/3 of thermal energy.
- worik 2y agoMakes the use of depleted uranium look benign Imagine thousands of soldiers with battery powered tools that must not(!!!) be dismantled So long as it happens "over there" I guess
- kccqzy 2y agoNuclear generation didn't always require a steam turbine. Radioisotope thermoelectric generator is an old tech that doesn't need any kind of turbines or liquids to function. It's still being used on the two Voyager spacecrafts. Of course it doesn't meet DARPA's requirement of bypassing the thermal middleman but it can be scaled to be reasonably small and can generate a few hundred watts.
- lupusreal 2y agoThe thermocouples those use are wildly inefficient and only make sense in cases where no moving parts that might break is the utmost priority (spacecraft, extremely remote lighthouses or radio relays, etc.) Betavoltaics are another option, which actually skip the thermal step, but those are only good for very small amounts of power.
- bitmasher9 2y agoThe issue with RTGs is that they don’t scale up, not that they don’t scale down. I’m not sure what the biggest RTG is, but they are usually measured in hundreds of watts. Then there is the issue of the radioactive waste. It’s useful for situations where refueling or maintenance are not options and access to solar light is poor. Pretty niche requirements, and the radiation issue limits applications to military levels of security.
- gweinberg 2y agoAug 30 seems like a ridiculously short deadline for proposals considering that this is as cutting edge as it gets.
- tconbeer 2y agoIt’s an RFI, not an RFP. They are basically looking to build a list of vendors who might be interested in bidding an RFP or competing in a domain-relevant contest.