As a newbie in nuclear fusion, this explanation is the most interesting part:
> Lee Margetts at the University of Manchester, UK, says that the physics of fusion reactors is becoming well understood, but that there are technical hurdles to overcome before a working power plant can be built. Part of that will be developing methods to withdraw heat from the reactor and use it to generate electrical current.
> “It’s not physics, it’s engineering,” he says. “If you just think about this from the point of view of a gas-fired or a coal-fired power station, if you didn’t have anything to take the heat away, then the people operating it would say ‘we have to switch it off because it gets too hot and it will melt the power station’, and that’s exactly the situation here.”
And the engineering here is very problematic. Indeed, the issue mentioned may be a showstopper for DT fusion.
The problem is limits on power/area through the wall of the reactor. Because all the produced energy has to go through the wall, and because the area of the wall grows as r^2, the volumetric power density of a DT reactor (that doesn't exceed the power/area limit on the wall) must decline with increasing size.
This leads to DT fusion reactors having horrible volumetric power density. ITER, for example, has a volumetric gross fusion power density of 0.05 MW/m^3. The 2014 ARC design, 0.5 MW/m^3. A PWR's reactor vessel? 20 MW/m^3.
On the other hand, basically every complicated bit of engineering on the PWR is due to the fact that it does have such a high volumetric power density. A PWR is basically a fancy (very fancy) pressure vessel which is cheap (in relative terms) and then parallel redundant cooling systems and containment buildings because dealing with such high power density is hard. Right after shutdown, the power density from decay heat is still 1.3MW/m3 and dealing with that decay heat in all currently conceived circumstances is where all the money goes.
What's wrong with pulling the energy from the magnetic containment system?
We already are using the magnetic containment system to redirect charged particles in the plasma back into the plasma. If we do so less forcefully than they were heading out, but still enough to stop them from leaving, we can convert particle velocity directly into electricity (AC with a relatively linearly decreasing frequency distribution, I think). This also has the effect of cooling the plasma (since temperature is related to average particle velocity).
The challenges I see here are:
1) The faster the control system, the more efficient it is at extracting energy -- it can extract the energy of higher frequency components.
2) You may need a very large magnetic field (larger than needed for containment) to make this practical
3) Coil geometry and efficiency becomes critical.
Euh ? In a few paragraph you basically say that even if fusion works, getting energy out of it will be almost impossible in a meaningful way (you're showing order of magnitudes of difference). But, don't the engineers at ITER and other facilities have already though about that ? It'd be very irresponsible to start such a project knowing in the beginning that, at the end, there's a high chance of failure...
An idle thought I had related to this is that the real trick to scaling up fusion power may be to not try and extract the energy "through the walls", as you said.
You know how they tell you to "visualise success" because you need to know what it looks like to aim for it?
Along those lines I was visualising what it would look like if someone like Elon Musk was on YouTube showing off some sort of future fusion reactor that's "not just a piece of lab equipment", but something that would be dramatically better than any extant fission reactor or similar technology.
I visualised it as an enormous stationary rocket engine, where cooling water was pumped through a relatively narrow (~50cm) "reactor tube". The water needs leave a hole in the middle for the fusion fuel gases. The hole is achieved by imparting a rotation to the water, so it "spins out" to the sides. Fusion would occur not throughout a large volume, but at a small number of "pinch points" along the axis set up using powerful magnets -- and not necessarily superconducting magnets! To get sufficient current through the coils, the charged exhaust is allowed to expand through a magnetic "rocket engine bell", producing moving (and accelerating) electric charges. This current is recirculated through the engine to provide the enormous magnetic field strengths required, via thick copper conductors aggressively cooled with water.
Essentially it would be a magneto-hydrodynamic-fusion jet engine, using fields instead of impellers to achieve compression, expansion, and energy recovery to run the whole cycle.
The bulk of the energy would be in the super-heated steam produced, which could be used as in traditional power plants, or used as a bone-fide rocket in space.
Obviously there would be "challenges" to making this work, to put it mildly!
But consider that with the kind of computer power we can throw at modelling physics these days, it may be possible to use "topology optimisation" style tricks to figure out the required geometry of the parts to achieve the conditions required for fusion while staying within material design constraints.
If you ask me, a Manhattan-project style attempt at something like this would be a better way to "waste money" than yet another aircraft carrier, or whatever...
Could the part of the plasma be diverted into heat exchanger and back into the stream somehow ? I guess problem there would be having one that doesn't just melt away. Maybe shoving water into it so it flash-evaporate and we're back to the ye olde steam?
Very wild idea: gaining electricity by induction instead heat since its charged matter.. but I know it doesnt make sense, as it only yields the kinetic energy which has too high entropy to be yieldable (no directed movement)..
Can the wall be baffled like an air filter to increase area? I get that the flux through it in total at a given radius would be the same, but is the heat being pulled out through plumbing or something?
Taking your number of 0.05 MW/m^3, Back of the napkin calculation is that the USA would need ~8,000 gigafacory-sized reactors to meet 100% of electricity demand.
Similar to how energy is extracted from fission reactors currently: the heat is used to boil water which makes large turbines spin and produce energy. It's dumb engineering. (I don't mean that in a bad way.)
I always find it slightly amusing how there's remarkably few forms of power generation that don't eventually boil down to "use water/air/steam to make a turbine spin".
It's a fusion reactor, so how do you get the water into the part with the hot stuff? That's all inside a magnetic field, I think. Also, you have to consider the neutron radiation's effect on the pipes that carry the water into the core, it's going to activate several metals in there, and cause weakening of the pipe wall, which will necessitate inspections and replacements.
It's a way harder engineering problem than you're letting on. Your comment is like a software user saying "How hard could it be just to add feature X?".
Could be interesting if they couple it with a Closed Cycle Gas Turbine [1] and a tiny steam plant, like the gas CCGT plants of today. Then the heat engine part should see similar, or even higher, efficiencies compared to gas based CCGT plants.
Boiling water using the Rankine cycle [2] and it will be as dead in the water as nuclear and coal is today.
A thing to keep in mind though is that it is very hard to compete with the engineering of an axle straight into a generator like wind turbines or a solid state system like solar PV. Working fluids, cooling loops and what not are awful to build and maintain.
It's also very expensive engineering. That's how a coal plant works, and the last coal plant that the US built cost $2B for a 600MW plant. Given how much cheaper solar & wind are, fusion will be dead in the water if it doesn't come up with a cheaper way of extracting energy from the reaction.
It's not my area, but I suspect that the heat extraction rate for a fusion reactor must be several orders higher than current fission reactors if we are to run them continuously. Fission reactions can be actively controlled by using reaction moderating material (control rods), which means we can tune the reactor activity to match the amount of heat extraction available.
Fusion plasma must be sustained at a few million Kelvin or it shuts down again, and I'm not sure how finely we can control the operating temperature without either overheating the reactor or shutting down the plasma. I think it will take a lot more than dumb engineering to accomplish this.
I was talking about this with the my kids (10, 7) the other day. Blew their minds a little that pretty much every power source comes back to the same central thing: moving magnets.
Then I pointed out that our electric car does it in both directions too.
Assuming we can run an actual fusion reactor consistently, how is the power taken out? I've seen lots of comments about water/steam, but we're talking 100M°C degrees here, that's insane! Do we bury this thing in the ocean?
I'm being silly, but I'm genuinely curious if there are any plans, even speculative ones, on how to do this.
The question is more how you get the heat to the water in a sensible way. It's _probably_ just engineering, but it's still something that needs to be worked out.
So we think about the engineering problem and reject the entire concept on that basis.
Even if I give you a magic box full of near vacuum 100 million degree plasma that emits 1MW/m^3 in the form of neutrons whenever you want as long as you stop it from touching the sides with supercooled magnets. How do you turn that into a remotely viable power station?
Just the heat exchanger and steam turbine portion is going to be uneconomical against renewables+storage.
Yes. Just just keeping a steam turbine up and running, completely ignoring where the heat comes from, costs more than both building out and operating wind and solar.
Right. It's not physics (though arguably plasma isn't that well understood but let's ignore that) it's just incredibly difficult engineering and needing to solve multiple extremely difficult engineering problems. In that same sense reversing climate change is just an engineering problem, populating Mars is just an engineering problem, a space elevator to orbit is just an engineering problem, quantum computers etc. etc. ;)
It's been considered, for a variety of heat sources. I'm long-term bullish on a related technology (thermophotovoltaics), although presently the efficiencies are not great & the compatibility with nuclear radiation is probably poor.
I still don't understand why we don't really have a reliable and good way to convert chemical bond/radioactive energy into electrical energy directly? Why do we still require 2 conversions of Chemical -> Heat -> Electrical ?
Is that something that is impossible or not cracked yet?
Fuel cells convert chemical -> electrical directly, batteries go both ways.
For nuclear fusion, the only practical reaction releases 80% of the energy as uncharged particles (neutrons), for which the only way to harness their energy is to convert it to heat. The 20% of the energy that is emitted as charged particles could in principle be converted with high efficiency, but the other 80% dominates.
For fission, more of the energy is emitted as charged particles, but it's not clear how one would harvest it directly in bulk. (It can be done on small scales, but not efficiently.)
Some examples exist for directly converting alpha, beta, and gamma particles into electricity, but I didn't find anything for neutrons in my brief search.
When I was at school in Abingdon, Oxfordshire (UK) around 1988 my physics class (A level aged 17) was somewhat enlivened by a visit by a bunch of clever chaps from JET at the Culham labs from up the road.
This was the first time I heard the "nuclear fusion is 25 years away" joke and it was told as such. We were also shown a graph of how many orders of magnitude away from ignition (for want of the correct word) by date. It had an initial steep decline but then turned right quite sharply and had annoying looking tendency to avoid the magic value.
Now, once you have ignition, you have to sustain it and extract power from it. That's quite tricky too!
We were also shown a graph of how many orders of magnitude away from ignition (for want of the correct word) by date
See p.4-5 of [1] for more recent plots. It includes earlier runs of both KSTAR (the experiment under discussion) and EAST (the Chinese one mentioned in another comment), but not their most recent ones.
TY and EoB and co were about three or four years ahead of me.
I recall watching "On a Friday" play on the cricket pav. of Abingdon School ("Royce's") at the end of term, summer '87ish. Thom did wear some very colourful waistcoats with his suit and Ed in mufti generally minced around wearing slippers, no socks and an electric blue jumper and a whopping quiff - as was the style in those days ("I fastened an onion to my belt..."). Actually this was the time of the New Romantics so think Culture Club, The Smiths, The Cure, Duran Duran etc.
History is what is written and WP is not keen on first hand experiences: "The band disliked the school's strict atmosphere ..." is writ on WP.
My perspective:
The school is a public school - so borders, dayboys and any school needs some sort of discipline. At the time it was all boys, I think it is now co-ed. However, next door there was the Park which was "no man's land" (master's and mistresses kept away and let the kids get on with it, provided we didn't take the piss) and both Abingdon boys and St Katherine's girls or Fitz Harry's or whomever could meet up and have a fag (smoke) and socialise in general.
We also had a bar in the cellar of School House for the weekends that was run by the boys and financed etc by us. Again, we were given a lot of slack, it was actually educational too - money in - money out etc. There was also the H&J (Horse and Jockey pub) - keep to the snug and look adult was what the owner told me as ordered a pint the first time (bless). I was in Waste Court House at the time.
My memories of Abingdon School are rather golden - I was extremely lucky to go there at the time. The Army paid for quite a lot of it. Nowadays it costs £40,000 a year to go there.
I would never describe Abingdon School as strict as such in the late 1980s when I was there. The Head was affectionately known as "Freaky Beaky" (a Headmaster is always the Beak) which is pretty standard for any public school. However, Mr Parker was also known as "Miffie" and that was down to someone overhearing his wife using a term of endearment.
At the time, obviously, there was no hint that On a Friday would go on and become a worldwide phenomenon but they were pretty good entertainment for a school band. They clearly had an itch to scratch and buggering off to the US and re-branding etc worked rather well. Well done them. It has to be said that Abingdon school was (with hindsight) extremely supportive. Mr Parker sanctioned On a Friday to play on the cricket pav for end of term entertainment.
Well spotted, and sorry, I seem to have started waffling on a bit ...
It's interesting to see that South Korea has such strong nuclear research facilities. Taiwan lost a lot of nuclear researchers in the past decades. Some of it due to US lobby work and some of it due to stupid governmental policies in the recent past. Japan which is also quite strong in nuclear seems to be trying to sell part of their nuclear industry, a move which turned out disastrously for the french.
More than half of their reactors are currently out of commission. And Macron was one of the people responsible for signing off on the deal that sold off their turbine development to GE due to pressure of the DOJ. They were talking about buying "it" back. Although I don't know what the scope or timeline of the buyback is. I also remember that contrary to previous promises GE started dismantling one of those factories.
South Korea also wasted recent years trying to shut down nuclear reactors and painting the nuclear industry as evil anti-environmental cabals. It's infuriating that Korea's politics is governed by either conservatives (who think environmental regulations should bend over for industries) or liberals (who think it's "eco-friendly" to shut down nuclear, when 44% of the electricity is coming from freaking coal).
This issue is not that simple to be framed as "painting the nuclear industry as evil anti-environmental cabals", like usual conservative propaganda. How many nuclear reactor actually has been shut down in last 5 years? Wait, zero? Yeah, the plan is shutting down reactors after its design life rather than blindly extending it more and more, which is the status quo.
Nuclear fission definitely has lots of advantages, but it comes with lots of geopolitical and operational challenges especially if you want to use it for decades, or so called "sustainability". One of the critical factor of "escaping from nuclear fission" was the fact that S Korea is not going to have permanent nuclear waste sites anytime soon; everyone have been talking about that over 30 years and no political party even dare to build the one because in S Korea, every single political issue eventually converges to a matter of real estate. And you know what? The capacity of the existing temporary storage for most plants will be exhausted within 5~10 years.
Now we're talking about the so-called "sustainability"; it's not about environment or whatever liberal propaganda but the dire facts that S Korea will be forced to shut down nuclear reactors unless it finds other ways around. The previous administration couldn't come up with a good solution so decided not to build more reactors. Oh yeah, they didn't even dare to shut down those reactors to earn a little bit more time. It's not even a propaganda, but just a mediocre compromise. Its territory is not big enough to construct just a single waste site.
Oh, then why don't we reprocess the waste? And now we're talking about geopolitical aspects. The US-Korea atomic energy agreement severely constrains what S Korea can do with the waste. Unlike many first world countries, it doesn't have the reprocessing technology and unlikely have the one unless it begins enjoying political tensions with the US.
Nuclear waste is just a tip of iceberg; you're going to find an arbitrary many number of operational and economical challenges on Nuclear fission reactor. And
I also want to mention general public reception on nuclear energy, "I trust nuclear energy, but not its operators". Yeah, Korean nuclear industry is well corrupted to its root and it deserves its own reputation. In the era of climate crisis, going to nuclear fission seems no-brainer, but the devil is in the detail.
The previous administration completely neutered its world class nuclear industry and built Chinese solar panels all over the mountain side causing landslides and environmental issues.
These are just some of the wonderful things the President Moon has accomplished.
> “This team is finding that the density confinement is actually a bit lower than traditional operating modes, which is not necessarily a bad thing, because it’s compensated for by higher temperatures in the core,” he says. “It’s definitely exciting, but there’s a big uncertainty about how well our understanding of the physics scales to larger devices. So something like ITER is going to be much bigger than KSTAR”.
This made me wonder when ITER was going to actually be up and running. From wikipedia:
> "The reactor was expected to take 10 years to build and ITER had planned to test its first plasma in 2020 and achieve full fusion by 2023, however the schedule is now to test first plasma in 2025 and full fusion in 2035."
So, it sounds like it'll start doing something within a few years, but it'll probably be a long time before it produces significant scientific results.
By the time ITER is running, maybe some other group will beat them to it (like the MIT ARC or SPARC reactors, which use more recent, better superconductors and don't need to be anywhere near as big).
One of the main reasons it's so delayed, is that everyone gets to make some of the parts. Which then have to be put together on-site, despite inevitable mismatches.
Reducing the number of countries involved will probably just speed it up.
ITER if ever finished will have exactly zero apparatus to extract useful power.
They are not even talking about starting on a power plant before 2050, or finishing before 2070.
It will of course all be dropped long before then, one way or another. Either we build out renewables fast enough, or civilization collapses before we get there. Either way, no fusion power.
Extracting useful power isn't really the point of ITER; the main thing is to operate the machine long enough to produce useful data that everyone else can use to build reactors that aren't based on technology that's several decades out of date.
I don't think ITER would be dropped because of renewables. Even if we had enough energy to power our civilization, there's always other things we could do if we had more. Civilization collapse could put a halt to ITER, but another possibility is the project could be dropped because someone else beats them to it and they don't need to finish this expensive machine just to find out what everyone already knows about magnetic plasma confinement.
"While the duration and temperature alone aren’t records, the simultaneous achievement of heat and stability brings us a step closer to a viable fusion reactor – as long as the technique used can be scaled up."
Half of the engineers on HN right now:
[...as long as the technique used can be scaled up...](PTSD_Chihuahua.jpg)
I don't know everything about nuclear fusion so I have to ask: Is it actually renewable?
In other words, are the byproducts able to form back into the "fuel" at a reasonable rate with the energy input of the Sun? I know that a selling point of fusion is that there is such an abundance of fuel that this doesn't matter. But if we treat finite energy sources as infinite, exponential growth in our energy budget means that we will undoubtedly run out of energy, as is being done with forests and such.
After all, I have a feeling people at the dawn of the industrial revolution thought the amount of coal available in the world would serve their needs "practically forever," until energy consumption scaled up by thousands of times.
So, the fusion we are talking about here is deuterium - tritium fusion as it should be the easiest to achieve. Deuterium is not a problem. A rough estimate says that there's enough of the stuff to cover 100% of the world needs for thousands of years. And it's easy to breed: surround the reactor with water so the hydrogen there can capture the stray neutrons.
Tritium, on the other hand, is a problem. It is radioactive with a half life of ~12 years and so the little we have needs to be produced since we can't really accumulate it. Currently it is produced by conventional nuclear reactors. Additionally, breeding tritium is harder than deuterium and requires a blanket around the reactor that uses other materials to multiply the number of stray neutrons. For each atom of Tritium that is fused we could get somewhere between 1.1 to 1.7 with a theoretical maximum of 2 Tritium atoms so, finally answering your question, it is renewable. It's just hard, but a piece of cake compared to actually maintaining a stable fusion.
Ultimately, no method of energy generation is truly renewable, including solar. The Sun will run out of fuel in five billion years, after all, give or take.
However, for all practical intents and purposes, solar energy is renewable. The same holds true for nuclear fusion for at least a couple of hundred years, even considering growing energy consumption.
Deuterium fuel is the most abundant. There's enough in your morning shower to supply all your energy needs for a year. There's enough in the oceans to last for billions of years. Fusion is as close to renewable as anything, because it'll last until the sun goes out.
Right now most projects are also using tritium fuel, which has to be made from lithium. That's plenty abundant but not to the extreme of deuterium. But pure deuterium fusion is possible, just a little harder. And one prominent fusion startup, Helion, is actually using deuterium (along with helium-3, which is the waste product of deuterium fusion).
By the point we've fused significant portion of Earths hydrogen, it will really not be a problem to hop over to Jupiter for some more. The scales are insane. Energy input of the Sun ALSO isn't renewable if you think like this.
People talking about fusion expect to "breed" tritium in their reactor. This takes the form of blasting GW of hot neutrons into a thousand (or ten-) tons of lithium hydroxide, and somehow extracting grams of tritium from it at parts-per-billion concentration.
There is no choice about that: it is the only way to get enough tritium to keep operating.
Readit News
> Lee Margetts at the University of Manchester, UK, says that the physics of fusion reactors is becoming well understood, but that there are technical hurdles to overcome before a working power plant can be built. Part of that will be developing methods to withdraw heat from the reactor and use it to generate electrical current.
> “It’s not physics, it’s engineering,” he says. “If you just think about this from the point of view of a gas-fired or a coal-fired power station, if you didn’t have anything to take the heat away, then the people operating it would say ‘we have to switch it off because it gets too hot and it will melt the power station’, and that’s exactly the situation here.”
The problem is limits on power/area through the wall of the reactor. Because all the produced energy has to go through the wall, and because the area of the wall grows as r^2, the volumetric power density of a DT reactor (that doesn't exceed the power/area limit on the wall) must decline with increasing size.
This leads to DT fusion reactors having horrible volumetric power density. ITER, for example, has a volumetric gross fusion power density of 0.05 MW/m^3. The 2014 ARC design, 0.5 MW/m^3. A PWR's reactor vessel? 20 MW/m^3.
(If you look at the power density of the plasma alone, or the fission reactor core alone, you get similar wildly discrepant numbers: https://cpb-us-w2.wpmucdn.com/research.seas.ucla.edu/dist/d/... see slide 26)
If you want to make heat to make steam to drive a turbine, a fission reactor will be much smaller, and much cheaper, than a DT fusion reactor.
We already are using the magnetic containment system to redirect charged particles in the plasma back into the plasma. If we do so less forcefully than they were heading out, but still enough to stop them from leaving, we can convert particle velocity directly into electricity (AC with a relatively linearly decreasing frequency distribution, I think). This also has the effect of cooling the plasma (since temperature is related to average particle velocity).
The challenges I see here are: 1) The faster the control system, the more efficient it is at extracting energy -- it can extract the energy of higher frequency components. 2) You may need a very large magnetic field (larger than needed for containment) to make this practical 3) Coil geometry and efficiency becomes critical.
What's wrong with a 3-6m size reactor vessel?
You know how they tell you to "visualise success" because you need to know what it looks like to aim for it?
Along those lines I was visualising what it would look like if someone like Elon Musk was on YouTube showing off some sort of future fusion reactor that's "not just a piece of lab equipment", but something that would be dramatically better than any extant fission reactor or similar technology.
I visualised it as an enormous stationary rocket engine, where cooling water was pumped through a relatively narrow (~50cm) "reactor tube". The water needs leave a hole in the middle for the fusion fuel gases. The hole is achieved by imparting a rotation to the water, so it "spins out" to the sides. Fusion would occur not throughout a large volume, but at a small number of "pinch points" along the axis set up using powerful magnets -- and not necessarily superconducting magnets! To get sufficient current through the coils, the charged exhaust is allowed to expand through a magnetic "rocket engine bell", producing moving (and accelerating) electric charges. This current is recirculated through the engine to provide the enormous magnetic field strengths required, via thick copper conductors aggressively cooled with water.
Essentially it would be a magneto-hydrodynamic-fusion jet engine, using fields instead of impellers to achieve compression, expansion, and energy recovery to run the whole cycle.
The bulk of the energy would be in the super-heated steam produced, which could be used as in traditional power plants, or used as a bone-fide rocket in space.
Obviously there would be "challenges" to making this work, to put it mildly!
But consider that with the kind of computer power we can throw at modelling physics these days, it may be possible to use "topology optimisation" style tricks to figure out the required geometry of the parts to achieve the conditions required for fusion while staying within material design constraints.
If you ask me, a Manhattan-project style attempt at something like this would be a better way to "waste money" than yet another aircraft carrier, or whatever...
1. What's the most efficient way to boil water?
2. How do we generate electricity on a population scale without having to boil water?
Question 1 is, apparently, much more tractable. We are still pretty much building the world's most sophisticated tea kettle.
It's a way harder engineering problem than you're letting on. Your comment is like a software user saying "How hard could it be just to add feature X?".
Boiling water using the Rankine cycle [2] and it will be as dead in the water as nuclear and coal is today.
A thing to keep in mind though is that it is very hard to compete with the engineering of an axle straight into a generator like wind turbines or a solid state system like solar PV. Working fluids, cooling loops and what not are awful to build and maintain.
[1]: https://en.wikipedia.org/wiki/Closed-cycle_gas_turbine
[2]: https://en.wikipedia.org/wiki/Rankine_cycle
Fusion plasma must be sustained at a few million Kelvin or it shuts down again, and I'm not sure how finely we can control the operating temperature without either overheating the reactor or shutting down the plasma. I think it will take a lot more than dumb engineering to accomplish this.
Then I pointed out that our electric car does it in both directions too.
I'm being silly, but I'm genuinely curious if there are any plans, even speculative ones, on how to do this.
Dead Comment
I believe the containers would have to be really large.
Also, if we have to continue boiling water at scale, we might reach water crisis some day. Although, it'd take very long time.
Even if I give you a magic box full of near vacuum 100 million degree plasma that emits 1MW/m^3 in the form of neutrons whenever you want as long as you stop it from touching the sides with supercooled magnets. How do you turn that into a remotely viable power station?
Just the heat exchanger and steam turbine portion is going to be uneconomical against renewables+storage.
When it comes to fusion I am always in too minds about statements like this.
On one hand, yeah, it is something that we may be able to wrangle into something useful.
On the other, fusion can be seen as a perpetual motion machine that doesn't defy the laws of physics. It can kind of inhabit that same mind space.
Why hasn't this been done? Why do we go to the steam stage when we could just exploit the termoelectric properties of temperature and current?
1. Thermoelectric generator: https://en.wikipedia.org/wiki/Thermoelectric_generator
2. Thermocouple https://en.wikipedia.org/wiki/Thermocouple
3. https://en.wikipedia.org/wiki/Thermoelectric_effect
A steam turbine is many times more efficient.
Is that something that is impossible or not cracked yet?
For nuclear fusion, the only practical reaction releases 80% of the energy as uncharged particles (neutrons), for which the only way to harness their energy is to convert it to heat. The 20% of the energy that is emitted as charged particles could in principle be converted with high efficiency, but the other 80% dominates.
For fission, more of the energy is emitted as charged particles, but it's not clear how one would harvest it directly in bulk. (It can be done on small scales, but not efficiently.)
https://en.wikipedia.org/wiki/Atomic_battery#Radiovoltaic_co...
https://en.wikipedia.org/wiki/Betavoltaic_device
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Dead Comment
This was the first time I heard the "nuclear fusion is 25 years away" joke and it was told as such. We were also shown a graph of how many orders of magnitude away from ignition (for want of the correct word) by date. It had an initial steep decline but then turned right quite sharply and had annoying looking tendency to avoid the magic value.
Now, once you have ignition, you have to sustain it and extract power from it. That's quite tricky too!
See p.4-5 of [1] for more recent plots. It includes earlier runs of both KSTAR (the experiment under discussion) and EAST (the Chinese one mentioned in another comment), but not their most recent ones.
[1] https://arxiv.org/abs/2105.10954
I recall watching "On a Friday" play on the cricket pav. of Abingdon School ("Royce's") at the end of term, summer '87ish. Thom did wear some very colourful waistcoats with his suit and Ed in mufti generally minced around wearing slippers, no socks and an electric blue jumper and a whopping quiff - as was the style in those days ("I fastened an onion to my belt..."). Actually this was the time of the New Romantics so think Culture Club, The Smiths, The Cure, Duran Duran etc.
History is what is written and WP is not keen on first hand experiences: "The band disliked the school's strict atmosphere ..." is writ on WP.
My perspective:
The school is a public school - so borders, dayboys and any school needs some sort of discipline. At the time it was all boys, I think it is now co-ed. However, next door there was the Park which was "no man's land" (master's and mistresses kept away and let the kids get on with it, provided we didn't take the piss) and both Abingdon boys and St Katherine's girls or Fitz Harry's or whomever could meet up and have a fag (smoke) and socialise in general.
We also had a bar in the cellar of School House for the weekends that was run by the boys and financed etc by us. Again, we were given a lot of slack, it was actually educational too - money in - money out etc. There was also the H&J (Horse and Jockey pub) - keep to the snug and look adult was what the owner told me as ordered a pint the first time (bless). I was in Waste Court House at the time.
My memories of Abingdon School are rather golden - I was extremely lucky to go there at the time. The Army paid for quite a lot of it. Nowadays it costs £40,000 a year to go there.
I would never describe Abingdon School as strict as such in the late 1980s when I was there. The Head was affectionately known as "Freaky Beaky" (a Headmaster is always the Beak) which is pretty standard for any public school. However, Mr Parker was also known as "Miffie" and that was down to someone overhearing his wife using a term of endearment.
At the time, obviously, there was no hint that On a Friday would go on and become a worldwide phenomenon but they were pretty good entertainment for a school band. They clearly had an itch to scratch and buggering off to the US and re-branding etc worked rather well. Well done them. It has to be said that Abingdon school was (with hindsight) extremely supportive. Mr Parker sanctioned On a Friday to play on the cricket pav for end of term entertainment.
Well spotted, and sorry, I seem to have started waffling on a bit ...
Any more to add?
IIUC, France has one of the highest percentages of nuclear energy of any country in the world.
Is this supposed to be bad?
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> Any more to add?
The Battle of Waterloo?
Nuclear fission definitely has lots of advantages, but it comes with lots of geopolitical and operational challenges especially if you want to use it for decades, or so called "sustainability". One of the critical factor of "escaping from nuclear fission" was the fact that S Korea is not going to have permanent nuclear waste sites anytime soon; everyone have been talking about that over 30 years and no political party even dare to build the one because in S Korea, every single political issue eventually converges to a matter of real estate. And you know what? The capacity of the existing temporary storage for most plants will be exhausted within 5~10 years.
Now we're talking about the so-called "sustainability"; it's not about environment or whatever liberal propaganda but the dire facts that S Korea will be forced to shut down nuclear reactors unless it finds other ways around. The previous administration couldn't come up with a good solution so decided not to build more reactors. Oh yeah, they didn't even dare to shut down those reactors to earn a little bit more time. It's not even a propaganda, but just a mediocre compromise. Its territory is not big enough to construct just a single waste site.
Oh, then why don't we reprocess the waste? And now we're talking about geopolitical aspects. The US-Korea atomic energy agreement severely constrains what S Korea can do with the waste. Unlike many first world countries, it doesn't have the reprocessing technology and unlikely have the one unless it begins enjoying political tensions with the US.
Nuclear waste is just a tip of iceberg; you're going to find an arbitrary many number of operational and economical challenges on Nuclear fission reactor. And I also want to mention general public reception on nuclear energy, "I trust nuclear energy, but not its operators". Yeah, Korean nuclear industry is well corrupted to its root and it deserves its own reputation. In the era of climate crisis, going to nuclear fission seems no-brainer, but the devil is in the detail.
These are just some of the wonderful things the President Moon has accomplished.
Which is why all three have/had such strong nuclear expertise.
https://en.m.wikipedia.org/wiki/Nuclear_latency
They are near / wary of China? That is why they have nuclear expertise?
This made me wonder when ITER was going to actually be up and running. From wikipedia:
> "The reactor was expected to take 10 years to build and ITER had planned to test its first plasma in 2020 and achieve full fusion by 2023, however the schedule is now to test first plasma in 2025 and full fusion in 2035."
So, it sounds like it'll start doing something within a few years, but it'll probably be a long time before it produces significant scientific results.
By the time ITER is running, maybe some other group will beat them to it (like the MIT ARC or SPARC reactors, which use more recent, better superconductors and don't need to be anywhere near as big).
https://en.wikipedia.org/wiki/ITER
Reducing the number of countries involved will probably just speed it up.
They are not even talking about starting on a power plant before 2050, or finishing before 2070.
It will of course all be dropped long before then, one way or another. Either we build out renewables fast enough, or civilization collapses before we get there. Either way, no fusion power.
I don't think ITER would be dropped because of renewables. Even if we had enough energy to power our civilization, there's always other things we could do if we had more. Civilization collapse could put a halt to ITER, but another possibility is the project could be dropped because someone else beats them to it and they don't need to finish this expensive machine just to find out what everyone already knows about magnetic plasma confinement.
https://news.cgtn.com/news/2021-12-31/China-s-artificial-sun...
Half of the engineers on HN right now:
[...as long as the technique used can be scaled up...](PTSD_Chihuahua.jpg)
In other words, are the byproducts able to form back into the "fuel" at a reasonable rate with the energy input of the Sun? I know that a selling point of fusion is that there is such an abundance of fuel that this doesn't matter. But if we treat finite energy sources as infinite, exponential growth in our energy budget means that we will undoubtedly run out of energy, as is being done with forests and such.
After all, I have a feeling people at the dawn of the industrial revolution thought the amount of coal available in the world would serve their needs "practically forever," until energy consumption scaled up by thousands of times.
Tritium, on the other hand, is a problem. It is radioactive with a half life of ~12 years and so the little we have needs to be produced since we can't really accumulate it. Currently it is produced by conventional nuclear reactors. Additionally, breeding tritium is harder than deuterium and requires a blanket around the reactor that uses other materials to multiply the number of stray neutrons. For each atom of Tritium that is fused we could get somewhere between 1.1 to 1.7 with a theoretical maximum of 2 Tritium atoms so, finally answering your question, it is renewable. It's just hard, but a piece of cake compared to actually maintaining a stable fusion.
Far more than that is available.
However, for all practical intents and purposes, solar energy is renewable. The same holds true for nuclear fusion for at least a couple of hundred years, even considering growing energy consumption.
Deuterium fuel is the most abundant. There's enough in your morning shower to supply all your energy needs for a year. There's enough in the oceans to last for billions of years. Fusion is as close to renewable as anything, because it'll last until the sun goes out.
Right now most projects are also using tritium fuel, which has to be made from lithium. That's plenty abundant but not to the extreme of deuterium. But pure deuterium fusion is possible, just a little harder. And one prominent fusion startup, Helion, is actually using deuterium (along with helium-3, which is the waste product of deuterium fusion).
There is no choice about that: it is the only way to get enough tritium to keep operating.
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