DARPA wants to bypass the thermal middleman in nuclear power systems | Hacker News Reader

DARPA wants to bypass the thermal middleman in nuclear power systems

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191 pointsbilsbie142 comments

Nuclear 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_64506...

    Not 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.

And set off all the NBC detectors on the highways near major cities.

Well yes but only if destroyed. Then wouldn’t you call that a feature? When in their enclosures there should be no radiation.

No way could all the alerts be tracked.

Yeah, you bring up another angle to look at it from: even if the alerts didn't go off when the batteries are being used/stored properly, it would make it easy to create a lot of noise/false positives as part of an actual attack (were those batteries to be readily available).

They were for a long time, betavoltaics were used in pacemakers. They started using more conventional batteries because the betavoltaics far outlasted the actual pacemakers.

That's interesting. I imagine parts for an internal medical device would be able to be more tightly controlled than batteries for general usage, but maybe I'm wrong.

Not Nickel-63 - Beta particles don’t go very far in air, and are shielded by almost anything. You’ll be unlikely to be alarming on beta emitters anywhere, unless they’re right up against your specialized Beta detector.

My understanding is, the danger with Beta emitters is if they are broken up into dust, and you breathe the dust in (or eat/drink it) then you are toast, as your lungs and internal organs get a small, but continuous bombardment of Beta particles which will eventually give you cancer.

If you are contaminated internally, with radioactive dust then there is no way to fix that.

Also nearly impossible to detect. No roadside detector will, anyway.

Without going into too many specifics, for a period during my career I was involved with an organization whose responsibility it is to track nuclear materials and keep them under safe surveillance—in fact my job had the words 'surveillance engineer' in its title.

I say that only bring to your attention how difficult this would be in practice. Putting safety aside for a moment, in most countries the regulatory restrictions are enormous because they are signatories to the NPT—Treaty on the Non-Proliferation of Nuclear Weapons which tightly bind them to how they use and handle nuclear materials. This involves, use, tracking, short and long-term disposal thereof not to mention how to keep radioactive materials away from bad actors/those who've ill intent.

With safety, there are so many issues involved that I can hardly even mention them here. Just as an illustration, the once lack of regulations covering the manufacture and use of luminous radium paint turned out to be a disaster.

I've thought about this a great deal, whenever the batteries in my flashlight die I wish I had some nuclear powered ones and evey time I'm brought back to reality when I think how difficult it would be to implement in practice.

I meant precisely what I said. Tracking NiCads to the standards of the NPT would presumably be impossible. If your standard is "keep it out of the food supply", though, I guarantee that there's a little bit of NiCad in that hot dog in your fridge, and there'd be much less NiCad in your hot dog if they tripped a radiation detector before they hit the incinerator or the landfill.

I've always said that I'm more afraid of heavy metal contamination then nuclear material contamination.

There are no hand held devices which will tell you if the soil you're vaguely near has heavy metals in it, nor how much.

There are no hand held devices which will tell you if the soil you're vaguely near has heavy metals in it, nor how much.

Well, technically, there are, but now you're back in the ionizing-radiation business: https://www.youtube.com/watch?v=KdfHVcU8U7U

I've been thinking for a while that there are so many possible sources of poisons it's very hard to monitor them all. But there is only one of me. So logically I should check if I have elevated levels of poisons. Then, and only then does it make sense to start monitoring my surroundings to trace where it came from.

Whether it's warranted or not is immaterial given the current situation with regulations and there seems little chance of that changing.

Personally, I've a healthy respect for radiation/nuclear materials but I'm not afraid to work with them so long as I know what I'm dealing with—and that's the key point. It'd be a bit pretentious to describe situations where I've been exposed to radiation levels above background except to say they were deemed occupationally safe. That said, I've always avoided such situations when and wherever possible.

Let's put my view into perspective: here's NileRed (a YouTube channel I like and watch often) making uranium glass in his home lab: https://m.youtube.com/watch?v=RGw6fXprV9U.

Note: I'd never do this despite the low level radiation because of the potential for breathing in uranium dust, albeit a small risk. That said, I nevertheless own several old wine glasses made from uranium glass which I keep not to use for drinking but as a demonstration of how uranium glass fluoresces under UV light.

It's very difficult to put information about radiation into proper perspective or in ways that the lay public can properly understand and appreciate, thus the need for tight regulations. Then, as I mentioned, there are the bad actors and of course a small collection of damn fools who are a danger not only to themselves but also to others.

No doubt, you're right about cadmium and traces of it in food. That comparison isn't lost on me either. It just so happens at another time I ran a business maintaining handheld portable cassette recorders of the type used in exhibitions, etc. and they used rechargeable NiCd batteries that needed replacement. It was not unusual for me to have to dispose of upwards of 500 old, often leaking batteries. Being concerned about Cd contamination and disposing of it in an environmentally-friendly manner was just part of the job.

Contamination from heavy metals is a very real problem and it's not only Cd but also Pb, Tl, Hg, As and orhers. Moreover, assessing the actual risk can be very difficult and depends very much on circumstances.

Like its more notorious mate mercury, cadmium is a poisonous heavy metal, nevertheless that hasn't stopped it from being used in industry for plating etc. (passivated cadmium plating makes a very nice surface). Thus, in the recent past cadmium has been deemed safe enough for these purposes in the same way mercury was considered safe enough for tooth amalgam/fillings. That said, just add a couple of CH3 methyl groups to Cd and we get one of the most diabolical poisons available—dimethylcadmium (same goes for Hg—dimethylmercury). Fortunately, these diabolical compounds aren't that common so we must take that into account when assessing the dangers of these heavy metals.

Heavy metals are everywhere in the environment both from natural sources and from pollution, so when assessing the risks several factors predominate, concentration and their potential for forming compounds that are far more toxic than are the base metals. Also, these compounds are often soluble which adds to their danger.

BTW, it's often been said that one cubic meter of soil from the average backyard has enough naturally occurring arsenic to kill someone—or at least sufficient to make them very sick. I've never seen assays to prove that one way or other but assuming it's true it puts the risks from heavy metals into perspective.

You can also order (natural) Uranium ore via the mail or on Amazon, some of which has pretty high disintegration rates and a decently high amount of Radium in it. 80-100k CPS.

Or just walk to a number of known sites in Utah and pick up chunks of ore off the ground.

A real danger IMO with Alpha and Beta emitters is that most Geiger counters aren’t going to pick them up at all - most are only meaningfully sensitive to Gamma.

"…(natural) Uranium ore via the mail or on Amazon, some of which has pretty high disintegration rates and a decently high amount of Radium in it."

I'm in Australia and there's no shortage† of the stuff here. Moreover, mining it has always been politically controversial.

Whilst it wouldn't happen now, when I was at school decades ago we had radioactive sources in the science lab and we did experiments showing how alpha rays could be stopped by paper, beta with tin foil and so on.

I also recall the lab had a round section of metallic uranium a bit bigger than a US silver dollar and about twice as thick, it was handed around the class for all to feel how heavy the element was. It was also a source of radioactivity for our Geiger counter (but not the only one).

To some degree, we have to be pragmatic about access to such materials but I'd be the first to agree that finding the right balance is difficult. Scaring everyone out of their wits about radioactivity is counterproductive (as we've seen in recent decades), similarly overfamiliarity is as equally dangerous.

I'm glad I had that early experience at school together with proper instruction that put its dangers into perspective.

The same went for mercury which we had at school in reasonable quantities. We were taught its dangers and to be very careful with it, especially so its compounds.

In recent times I've met young people who've never actually seen mercury and who are terrified of even the mention of it. Clearly no one ever wants a repeat of the Minamata tragedy but being scared of elemental mercury to this extent isn't right either.

I've often said our best approach is proper education, that is by providing factually accurate information from early on.

Seems to me in recent years we've not done a particularly good job at doing that.

† https://en.m.wikipedia.org/wiki/Uranium_mining_in_Australia

https://en.m.wikipedia.org/wiki/Radium_Hill

> With safety, there are so many issues involved that I can hardly even mention them here. Just as an illustration, the once lack of regulations covering the manufacture and use of luminous radium paint turned out to be a disaster.

I think it's telling that the big health disaster everyone remembers happened like a hundred years ago and occurred not just before regulation, but before the danger was even understood. There are negligible annual deaths in the US from either acute radiation exposure or nuclear-material-related chronic radiation exposure.

Three US workers died in 1961 when the SL-1 reactor went prompt critical and the core explosively vaporized.

All up there are at least seven or eight fatalities in US reactor | research facilities in that general time frame, Los Alamos National Laboratory, et al.

The Columbus radiotherapy accident 1974-76 led to 10 deaths and 88 "immediate severe complications"

There was another in Houston in 1980 with 9 deaths and additional complications.

https://en.wikipedia.org/wiki/SL-1

https://en.wikipedia.org/wiki/Columbus_radiotherapy_accident

REAC/TS Radiation Accident Registry: : https://www.irpa.net/irpa10/cdrom/00325.pdf

Thanks but I think this proves my point? A handful of deaths each decade, in an industry with hundreds of thousands of workers. Like, being killed by a falling I beam or in a car accident while commuting to work are vastly more likely.

I agree with your point; there are negligible annual deaths in the US from meteorite strikes.

I've had a career mapping environmental radiation across entire countries; background uranium, potassium, and thorium and residual traces from testing, mining and accidents.

Deaths are rare in the US, a bit more common elsewhere, that's a fact.

I can't say that's an argument for relaxing standards or being less safety conscious in reactor design, building codes, or medical and industrial procedures.

The Union Carbide Corporation (UCC) of the United States demonstrated pretty well what can happen if you shirk safety and that was just manufacturing pesticides.

There's always that one meteorite.

Mind you, there's a steady supply of radioactive waste from rare earth processing that gets offshored and swept under the carpet .. it's okay to have an addiction to fancy electronic gadgets, less so to be ignorant of by products and the harm caused in other peoples backyards.

> The Union Carbide Corporation (UCC) of the United States demonstrated pretty well what can happen if you shirk safety and that was just manufacturing pesticides.

> There's always that one meteorite.

But we just ignore the meteorite. Nobody has made any attempt to stop either of us being hit by a meteorite. We just let it fall where it may.

We've had safety standards shirked, we've had multiple disasters and the worst case scenario so far appears to be order-of-magnitude equal to a normal year of current practice using fossil fuels. It seems to be well within our tolerance for risk.

The issue here is that progress on one of the most promising sources of energy we have has been blocked and it is hard to find someone who can articulate a reason why, let alone a good reason. Between Germany and Japan we've had countries that appear to be more willing to risk deindustrialisation than just keep on with a perfectly acceptable nuclear status quo. It is madness. It is akin to trying to move civilisation underground to avoid the inevitable meteor strike that is going to wipe out humanity - we can't afford that expensive a risk mitigation and it doesn't seem clear that it would even help.

'We' is doing a great deal of heavy lifting for you there.

South Korea has fast build times, China has 100 reactors planned with 10(?) (IIRC) currently under construction, a large MW scale pilot SMR completed and tested for a year, ground broken for a low GW 2nd gen salt reactor based on the pilot, and plans for a large high GW third gen version waiting on the 2nd gen being completed and bedded in for any modifications to plan.

The economics vary by country and demand, here in Australia there's no economically feasible near term path for nuclear power gen. for a number of good reasons, not the least being the short term return from putting any available money into renewables and batteries - but this is a particular economic constraint setup that differs to other countries.

> Deaths are rare in the US, a bit more common elsewhere, that's a fact.

> I can't say that's an argument for relaxing standards or being less safety conscious in reactor design, building codes, or medical and industrial procedures.

It's prima facie evidence you're picking the wrong trade-off between safety and productivity. Because of the nature of diminishing returns, the optimal point in a cost-benefit trade-off usually results in both non-negligible cost and non-negligible benefit. When your safety regs are so strong as to have driven risk to ~zero, but where the compliance cost of the regs are reflected in every aspect of the industry, there ought to be a presumption of over regulation that would need to be rebutted quantitatively. It's irresponsible to set degree of regulation without estimating the costs of compliance.

With the caveat that I'm not picking any trade-off other than the time cost involved in looking up a few incomplete answers to forum questions that catch my interest;

it's extremely difficult to evaluate industry (broad industry, not just nuclear) safety value on the basis of deaths that have occurred without a solid understanding of the deaths and other costs that can occur should standards be relaxed.

The analysis on various Los Alamos et al. National Laboratory incidents during the early atomic days reveals that things easily could have been much worse, rather than three dead greater numbers could have been killed and expensive facilities rendered unusable. Carrying live but "safe" nuclear weapons about came razor close to accidental detonation on US soil near civilian population centres on a few occassions - these make studies for whether safety procedures were justified in time and expense or perhaps barely went far enough.

I raised Union Carbide Corporation as an example of what can happen in an industry if safety isn't headed, such accidents can happen in many industries and some have the potential to "salt the earth" for many many years past an event that immediately kills large numbers.

    Timing Toast

    There's an art of knowing when.
    Never try to guess.

    Toast until it smokes and then
    twenty seconds less

suggests the pragmatic answer to the question you pose is to reduce regulation until an acceptable death threshold is crossed and then regulate a tiny bit harder.

This can be difficult to do in practice.

We spend billions and billions on the industry each year. Most risks are not Chernobyl, they are Larry exceeding his defined annual dose by 30%, necessitating a plant-wide work stoppage to prepare a 300 page report on the root cause.

Yes, now how many people die from coal-related pollution every day? Heck, a single middle-tier dam failure probably killed more people that have died to nuclear accidents in history.

I'm not makiing a case, a question was asked and I answered wrt direct deaths from radiation accidents.

Some coal related pollution deaths can easily fall under indirect deaths due to radiation.

By all means lookup and answer your own question, HN threads benefit from solid figures and linked sources.

Maybe the reason for the low number of deaths is the high levels of tight regulation.

Yeah, I was about to say.

We consider it safe because it’s tightly controlled and very centralized, but that has no connection to how safe it would be as a consumer product. Just because it contains the same material, doesn’t mean anything, because the methods of harm that could emerge have never existed.

Ingestion, trash disposal, recycling contamination, the infinite ways you could accidentally destroy a device.

Of course. But whenever you're balancing downside X against upside Y, and the downsize is now essentially zero, this is prima facie evidence you're picking the wrong trade-off.

> I think it's telling that

That's putting the cart before the horse.

Those regulations came to be because of things like that (plus also "we don't want everyone getting nukes or radioisotope weapons" because this is more general than just industrial accidents).

The only way to compare is to look at times (or places) without the legislation.

I regularly see thrown away batteries on the streets of Amsterdam. This worries me.

Meanwhile and just a few days ago…

“Rising rates of cancer in young people prompts hunt for environmental culprit (ft.com)”

https://news.ycombinator.com/item?id=41178776

I think a NiCad is a lot less dangerous if it does get broken up. Once such devices are ubiquitous, that means improperly handled/disposed ones will also be ubiquitous.

Pretty dangerous when burned though.

> "... 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...

If my maths is right (and it's past midnight, and I'm not entirely sober, so might not be) and my search results are too, 15 x 15 x 5 cubic millimeters is approximately 9.68 times smaller than an iPhone battery (95 mm x 37.6 mm x 3.05 mm, ish), but if energy capacity scales linearly to volume then its ~12,500 times lower capacity per volume than an iPhone battery.

That’s 100 microwatts x100 years, so about 876 wh, or 292 amp hrs (292,000 mah)

But, still, only 80mah a day . So 750mah scaled up to iPhone battery size. So abut 1/5 of the average daily power requirement for an iPhone. Even at that rate you’d need to use a supecapacitor to even out the load profile.

OTOH, in terms overall energy, it would be about the same as about a 50 litre lithium ion so it is rediculously dense, just low output

1/5 the daily power requirement is surprisingly decent. Swapping out the screen for an eink display or ultra low power LCD like those from PixelQi and downclocking the SoC might be enough to make up that gap.

FYI, your comment made me look up PixelQi and Wikipedia says that conpany died almost a decade ago (although 2015 feels to me like much, much less than a decade ago):

> "By 2015, PixelQi's team and offices were unreachable, and the company is presumed defunct.[3] The intellectual property is now owned by the original investor of Pixel Qi, while the right to manufacture Pixel Qi technology contractually rests with Tripuso Display Solutions.[4][5]"

https://en.m.wikipedia.org/wiki/Pixel_Qi

Or half the battery size that came with the iPhone 4s.

It could be made to work if software wasn't so violently inefficient (both CPU and data usage) and screens weren't so large.

TFA states this and replies to this, in detail :)

In 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

It’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.

That sounds very cool. Like a nuclear ion drive. Is there a technical paper about it?

Sounds like what Wikipedia calls a "Fission-fragment rocket", I think?

So check the citations for papers:

https://en.wikipedia.org/wiki/Fission-fragment_rocket

Very interesting - I had not heard of this before. I see that the entry on the “dusty plasma” design says that the exhaust flow can be decelerated for power (presumably that applies to other designs as well.) It does not mention how the deceleration is performed (electrostatically, a bit like a reverse Van der Graaff particle accelerator?) or how efficient and compact this could be.

Wikipedia has a short list: https://en.wikipedia.org/wiki/Direct_energy_conversion

Now knowing that small quantities of space dust settle on our roofs, I presume you'd have to reach some safe distance from populated planets before using such an engine?

Orbit is sufficiently safe. The exhaust products are individual atoms rather than grains of rock that can fall on a roof.

Yeah, but those atoms are fission products!

Eh, they're moving at 3-5% the speed of light. Just don't point it towards the planet.

One of my fav. points in one of the classic sci-fi books (a deepness in the sky maybe?) is how the main engines of their ships (bussard ramjet fusion drives) were also such incredibly powerful weapons, that merely pointing one (even when off) at anyone was seen as a clear declaration of war/hostile intent.

Which, if you do the math, is definitely the case. Ain’t nobody walking away from getting one of those to the face.

Yes, Vernor Vinge’s A Deepness in the Sky had Bussard ramjets, and using one inside a civilized solar system was usually a great crime since the magnetic fields may be extremely large. But you can’t point them; they’re more of an area–effect weapon.

Larry Niven’s Known Space stories coined the phrase Kzinti Lesson when a peaceful Human crew turned their photon drive on an attacking Kzinti ship, slicing it in half. The Kzinti had acquired an anti–gravity drive from aliens (who they then enslaved and ate) so they didn’t have a good visceral sense of the energy required to visit the stars the hard way. Their telepaths kept reporting that the Humans were peaceful and didn’t have any weapons on their ship right up until the ship flipped over and sliced them in half. That kind you can point.

I thought the Fusion Drive plume also came up - but perhaps I’m thinking of a different book?

At the accelerations most sci-fi happens at (even fractions of 1G), the energy coming out the business end of any sort of drive based on extrapolations of currently known physics are going to be in the TJ+ range, and often with relativistic particle velocities.

Probably not as focused as a laser type drive, but in a vacuum such a fusion type drive would melt any known materials at multi-km distances and likely cause extreme x-ray emissions from whatever it was vaporizing when it came in contact with it. In atmosphere, it would likely just vaporize the space craft along with anything in a several mile radius.

It’s basically carrying around a directable, continuously exploding hydrogen bomb.

Irrelevant. They are moving fast but they are tiny individual atoms. There would be no harm in having them impact the atmosphere. They would bump into a few thousand or perhaps a million gas molecules on their way down to the surface, turning their tiny kinetic energy into a tiny amount of heat. And since there is only a few kilograms of fuel, there can only be a few kilograms of exhaust. With a low thrust and high specific impulse, the engine would burn that fuel continuously for most of the trip, spreading the exhaust from here to Pluto and back. It’s not going to be sufficiently concentrated to bother anybody.

In fact, even though the fuel pellets are only about 1µm across, they still bump into enough atoms on their way out that the pellets heat up significantly. A major engineering consideration of the engine would be to absorb or deflect the heat radiated by the >1000°C fuel pellets without letting that heat quench your superconducting magnets.

On the one hand, I also think it's likely safe: we've had a huge nuclear reactor in the sky since before life happened, the atmosphere and the magnetosphere are pretty effective barriers. (I think they're more worried about actinides than impactors).

On the other, I'm not sure where your 15 kg came from.

This matters, because fancy fuels matter a lot more for higher-mass or high-Δv payloads than smaller ones.

A fission fragment rocket can be Isp of 1,000,000[1] depending on the exact details — thrust is proportional to momentum (mv), not energy (0.5(mv^2)), and that means four million times the energy density is two thousand times the momentum and thrust, so that 15 kg is like 30 tons of conventional propellant: a nice saving, but you'd use a lot more than that for e.g. a manned mission to Mars.

For missions where the payload rather than the speed is critical, fuel is also a small fraction of total mass, so you also get a performance boost from being able to approximate the Tsiolkovsky rocket equation as linear.

But that's perhaps another factor of 10, which is still roughly 25% of a Starship upper stage, so even then I'd expect at least 60 kg even if the engine itself can be considered negligible in both cases.

And that's likely to be burned through much sooner than Pluto, though it depends on the details of the design. The ship would likely melt if you tried to thrust at 1 gee, but I think it would still be comparable to the Earth-Moon distance, give or take a factor of 3.

If you want something that burns from here to Pluto, then… huh, I was going to say you're likely back in Tsiolkovsky's realm, but apparently still not, and also still sub-relativistic (~ 1 milli-c for the specific values I was using).

Which is still safe, I just don't think it's quite as trivial as you say.

[1] https://en.wikipedia.org/wiki/Fission-fragment_rocket

Honestly, I might have misremembered the fuel mass. I tried looking for the paper I read about this design, but I couldn’t find it. It’s been a whole year since I read it, and I guess they don’t think hosting it is useful anymore.

But they’re also just individual atoms. They’re not a chunk of radioactive material that can sit on your roof for years.

Besides, the whole ship would have maybe 15kg of fuel. That means that there can only be a maximum 15kg of fission products. It would burn fuel that for several years, spreading the exhaust out over the distance from here to Pluto and back.

Atoms are atoms, by definition.

> which fly apart at about 3% of the speed of light, due to Coulomb repulsion

So is that at first an electrical force that results in kinetic acceleration?

What do you mean by "at first"? The protons are pushing each other away via that Coulomb repulsion while they're all in the pre-fission nucleus, but at that time it's not enough to counteract the strong force (https://en.wikipedia.org/wiki/Strong_interaction) holding the nucleus together. Once that once nucleus has been split into parts that can move freely, the daughter nuclei are both accelerated by an electromagnetic force.

Well, yeah, once the distance gets out of the well of the strong force, the nuclei are at the top of a big electrical force gradient that gets converted to kinetic energy. With proper ionization of the daughter atoms that kinetic energy could potentially be converted back to electric, well, potential.

This 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!

Helion 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.

Commercial energy company. Not fusion company. There are no fusion companies on this planet yet.

What do they plan on using to generate energy then, oil, coal, solar, wind? Something else?

So far: looks like hope and promises rather than any of those.

They 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.

They'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.

Eh. They don't sell anything of immediate utility. But they definitely sell fusion.

Think of it as a conspicuous luxury handbag for weird finance/tech bros. "Oh yeah? Well MY investments are going to save the world!!!"

Fusion is infinitely harder for this than fission. No company has demonstrated stable fusion with a positive net energy gain. Most of these startups are borderline scams for milking gullible VCs. Helion in particular has been around for more than a decade and was supposed to reach break even in 2023. They haven't even achieved a fully stable D-D reaction so far. The biggest thing it has achieved is siphoning tons of money from OpenAI's investors because of some questionable actions by Sam Altman.

Fusion overall is harder than fission.

Is the direct energy capture part also harder for glowy fusion gas than scary fission rocks?

I think the concepts are the same but the execution (heat up water with plasma) is still a work in progress.

That's the "thermal middleman" part they're trying to cut out.

By analogy, compare Concentrated Solar Power versus Photovoltaics.

I think in a Deutritium-Tritium fusion reaction a lot the energy is in the neutron. And since neutrons are neutral you can't really directly convert that into electrical energy.

Yep, for D-T 80% of the energy is in neutrons. Helion is using D-D/D-He3, and for that it's about 5% in neutrons, and most of the rest in fast-moving charged particles.

So they have a simple way to extract electricity directly. They squeeze the plasma with a magnetic field from a copper coil, then there's an explosion of charged particles, which pushes back against the magnetic field and causes electricity to flow in the coil.

D-D (which they are going for right now) is still 50% neutrons. D-He3 is the only aneutronic reaction, but it has tons of other issues.

As I said, the combined reaction generates 5% of its energy as neutron radiation. The reason it's only 5% is that D-He3 is a much more energetic reaction.

The main issue with D-He3 is that it's more difficult.

That's what I said. But all things equal, D-D is definitely not the best path for direct energy production because of the vast amount of neutrons.

What do you know that all those investors don't that lets you so confidently call this a borderline scam?

I have seen this whole scheme play out more than once by now. Helion is not the first fusion startup. Not by a long shot. It's just one of those who gathered media attention (and even that was not due to their science but to OpenAI's business practices). If you're an investor, you're welcome to hire me as an adviser and I'll tell you exactly where and how they are being delusional or outright dishonest. But most investors get hitched on nice pitch decks and certain keywords or names.

It's a pulsed reactor by design, it's not supposed to create a "fully stable" reaction.

They're actually pretty much on schedule, once you account for the several years it took them to get the necessary funding.

All of those experiments say they are "on schedule" for whatever schedule they made up for this year. If you have been following this for as long as I have, you'll know that these statements are worth nothing.

You're the one who referenced their earlier published schedule, which said they were "supposed to reach break even in 2023." They had a couple years of delay in funding after making that statement.

All the more reason not to trust any schedule laid out by them this time.

There definitely trendy since some high profile YouTubers were invited to tour! I sincerely hope they can succeed. I believe a limiting factor is going to be fuel unfortunately, as well as I’m not entirely sure it’ll be radiation free.

The original fuel is deuterium, which is absurdly abundant on Earth. Pure deuterium fusion results in half helium-3, and half tritium which decays to helium-3 with a 12 year half-life. Then their main reaction is D-He3.

The D-D reaction is less energetic and produces a neutron, and the D-He3 reaction doesn't produce a neutron. The combined reaction would release about five percent of its total energy as neutron radiation. The neutrons from D-D are about as energetic as fission neutrons, rather than the extremely high energy of D-T fusion neutrons.

They'll never run out of fuel; there's enough deuterium in your morning shower to provide all your energy needs for a year. But the need to breed He3 will put a limit on how fast they can possibly scale up. It could be that manufacturing will be slower than that anyway though.

Thanks for the insight. I remember it being like the raw ingredients were plentiful, but the main reaction ingredients were not.

I don't remember the details, but the last time I looked into Helion I came away with the belief that their technology flat out doesn't make sense and will likely never be anywhere near net-positive. Like, the numbers literally don't add up and their design could never be anywhere near net-positive.

I had the impression that the energy flux required to break even is higher than any known materials can support, at any geometry. I really hope that's wrong :-)

Can someone who has a firm grasp on this stuff explain to me how nuclear reactions don’t create massive amounts of electromagnetism that we can just capture directly? Is it really just heat that it produces?

They kinda do. When a fissile atomic nucleus splits, the daughter nuclei repel each other; they are both positively charged and the strong force is no longer holding them together. So they fly off in opposite directions at a measurable fraction of the speed of light. But they don’t generally get very far, because they are embedded in a solid fuel pellet. They can push their way through a few µm of uranium before they are stopped, bumping into thousands of atoms along the way. That’s really where the heat comes from; all that electrostatic force accelerates them to high velocity, but they dump it all very quickly into the material around them as heat.

> Is it really just heat that it produces?

Yep, it's a big nuclear powered boiler. Boil water, get the steam, spin the turbin, cool the water, repeat.

It’s amazing how many generators basically boil down to the same ‘boring’ process of ‘boil water. spin turbine. repeat.’

I mean, that's just because water is a simple medium we can just literally trow out in the environment after use, using basically anything else to spin said turbines would require a closed system and cooling.

Gravity batteries could be a thing but pumped water is the best version of that system, in this case we don't boil the water tho

Water has really awesome phase change properties and is nearly ideal for this kind of situation too. Only thing better is potentially super critical co2.

It generates high-speed neutrons, helium cores, photons, fissile fragments, and in rare circumstances free protons.

Of those, only the protons have an electric charge you could use in any form of generator… but I’m not aware of any form of reaction that predominantly creates protium. The fragments are also charged, but the implication that you’re using fission means they’re in the middle of a block of uranium and won’t keep their speed for long.

The others ignore electromagnetic fields for the most part, and will fly around until they smash into something and go goooong like the world’s smallest bell. Or smash through something, perhaps; it’s a chain reaction after all.

This mostly just makes other stuff move about. Repeat a few dozen times, and you’ve got heat.

The helium nuclei a.k.a. alpha particles are also charged, like the free protons.

However, the alpha decay of some product of the fission reactions does not change the total charge of the fissile material, because the emission of a helium nucleus with a double positive elementary charge leaves a heavy nucleus with a diminished nuclear charge, by those two elementary charges.

Only when the alpha decay happens to occur close to the surface of the material, the positive helium nuclei may escape from it and they could land on a collecting electrode, making that electrode positively charged and leaving the fissile core negatively charged. However such a process would extract only a negligible part of the energy produced by fission. Even if the alpha extraction could be enhanced somehow, the decay energy of the fission products is small in comparison with the energy produced by the initial fission of the uranium nuclei. Extracting directly from the fissile material the nuclei generated by fission would be much more difficult than extracting the helium nuclei.

The Darpa project may succeed to stimulate the creation of some electric generators that could deliver additional energy from a fission reactor, by direct electric charge separation, but that would remain a small part of the total fission energy, most of which will still have to be extracted through thermal methods, like today.

  2D  + 3He → 4He + 1p  + 18.3 MeV
  3He + 3He → 4He + 2 1p  + 12.86 MeV

I 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.

Of 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.

Could this cause a resonance cascade?

Unlikely 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.

If 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.

Mayne one could run it in the visible range, or almost there. Wasn’t there some new kind of IR solar cells?

You have to go the other way of the spectrum toward something that loves to avoid interacting with matter...

Finally a use for dark matter

But dark matter is matter that doesn't react very much with radiation (including light), so it would react even less.

I 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

Yes, I see how direct conversion could work with alpha and beta radiation, but it seems the gamma and the neutrons would just blast through everything and you'd capture only a tiny percent of the energy.

Sorry, I was responding to the part about IR.

We 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.

Nuclear 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.

The 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.

The 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.

What's the typical efficiency of a nuclear power plant? i.e. what fraction of the energy from the fission reaction gets converted into electricity?

I remember something like 1/3 of thermal energy.

One 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

This 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.

As 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.

There'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.

And 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.

Ammonia, Methanol, etc - Fertilisers and fuels for marine shipping in addition to being transportable "energy" that's less slippery than hydrogen and can travle further than an HVDC transmission line "extension cord".

Currently green hydrogen plants are expanding and ammonia | methanol marine fuel ships have been built and trialed - there are contracts signed and in the works to both build a 4,000 km HVDC "suncable" and to ship hydogen products longer distance.

You pipe it somewhere and burn it, in a heater, or an engine, or a smaller generator, the way natural gas is used today. Or fill a tank with it and power a vehicle.

However, I appreciate the point made about hydrogen escaping and causing embrittlement of materials.

You want to use thermal energy to make hydrogen, then burn that hydrogen to make thermal energy, possibly even to harvest that thermal energy to produce electricity...

The idea is that nuclear fission produces thermal energy, the production of hydrogen provides a means of storing and transporting that energy to its point of use. It might be useful to draw a diagram.

Electricity is really just another means to the same end. You can't use all of the energy generated by a power plant, at the plant site, so you transport the energy to places where it's needed.

Aug 30 seems like a ridiculously short deadline for proposals considering that this is as cutting edge as it gets.

It’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.

This 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.

If they utilize the waste heat for eg. district heating, the equation looks a lot better. Unfortunately most cities don't have district heating.

There 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.

You 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.

Some district heating systems do in fact use steam.

Losing 50%-67% of the energy to waste heat is not the roadblock to new nuclear.

The roadblock is the immense expense of a massive, complicated, intricate machine requiring massive workforces of highly skilled construction labor.

Shifting from heat conversion to some sort of direct conversion, and in the process ideally eliminating a huge amount of the construction expense, is the way out.

As our economies become ever more advanced, skilled labor becomes ever more expensive. Our existing fleet of nuclear reactors is much like the intricate cathedrals of past centuries. We could build in that style, but the expense is much higher today than it was back when the cathedrals were first made.

You mentioned energy efficiency, I simply provided a possible way to boost that efficiency up a bit.

You are right! I must have been thinking of different types of efficiency and written very unclearly. A pet peeve of mine is people talking about "efficiency" in energy and not defining it or switching between definitions sloppily, and I seem to have done it there. In any case apologies for not being consistent.

But why is it so hard. A steam engine in itself is not complex, we had locomotives for a long time, they didn't have high performance welding for example. Why can't we dumb down nuclear reactors? While keeping it safe. Perhaps by using material that won't cause meltdowns or using heat from nuclear waste?

If you have 20,000 welds that each need to last 30 years without being fixed later, that's an order of magnitude difference in quantity than the corresponding 2,000 for a coal boiler, in addition to a few orders of magnitude difference in the necessity of lasting a long time without repair.

It's a hell of a lot more than a steam boiler, even if ultimately that's the goal. The nuclear island is a hell of a beast of complexity, size, and quality.

Makes 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

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