Former fusion scientist on why we won't have fusion power by 2040

there's a famous saying that nuclear fusion is 30 years away and always will be but not anymore it seems the united kingdom's atomic energy authority is promising an operational reactor in 19 years several startups are targeting 2030 or sooner lockheed martin is promising to have a working prototype two years ago just as soon as their time machine division is ready with their project in this video i will try to explain why fusion energy will unfortunately probably not be used to power any part of our electrical grid by 2040 all sources are in the description it takes a lot of time and planning to build a major infrastructure project even when it's a long proven technology like an airport or a rail line if you had the money in hand today you'll be lucky to build an airport in nine years building a major nuclear site with the handling of radioactive waste would make things many times harder for an experimental and totally unproven nuclear technology like fusion the challenge of ironing out all the problems which arise in a couple of decades is nearly insurmountable suppose you can overcome all the boring logistical challenges you will discover that actually carrying out fusion reactions is both surprisingly easy and surprisingly hard fusion is a nuclear reaction whereby lighter atoms combine into heavier ones as long as the atomic weight of the final product is less than that of iron or nickel energy will be given off two oxygen atoms could fuse into a sulfur atom and release energy for example the challenge is that nuclei are positively charged and hence repel each other the larger and more charged the nucleus the stronger the repulsive force conversely hydrogen has the weakest charge and its isotopes are the easiest to force together the reaction of deuterium one proton and one neutron and tritium one proton and two neutrons is the one which happens most readily of all and therefore the one all the experiments are targeting two deuterium atoms can also fuse very easily the repulsive force could be overcome if one of the nuclei is held fixed and the other is accelerated through a voltage of hundred 000 volts this is surprisingly easy you see the reason youtube is called youtube is that when i was a kid we used to have tvs and computer screens based on a type of particle accelerator called a cathode ray tube one of which i bought for 50 bucks crazy i know but for just 50 dollars my tv could have accelerated hydrogen isotopes through 20 000 volts or a fifth of the way to reliably achieving fusion for a larger but not exactly astronomical amount of money i could have built a dedicated souped-up version of this type of device called a fuser this is just what a kid called taylor wilson did when he was 14 years old his fuser accelerated deuterium so that a small fraction underwent fusion and released energy the problem is that no matter how big or small or how it's configured the energy produced by a fuser could never be turned into more useful electricity than it consumes to explain why try the following for me rub your hands together to generate heat by friction due to fundamental physics like the second law of thermodynamics it is not practically possible to turn that small amount of heat into electricity that heat will escape into the atmosphere and despite humanity's best attempts to blanket the earth and greenhouse gases it will eventually be emitted as infrared radiation into space simply enabling fusion reactions is not good enough to generate electricity the reason i'm stressing this point so much is that many of the startups say they will demonstrate or do fusion on their roadmaps to attract investment this is what the kids are calling a nothing burger there is no substance there it's impressive for a 14 year old but for a multi-million dollar company this is trivial and just as with taylor wilson's fuser demonstrating a small amount of fusion reactions is in no way a guarantee that the method could ever even theoretically be scaled up to produce electricity to have any hope of generating useful power we would need to do what is called thermonuclear fusion in basic terms you must first heat your fusion fuel to enormous temperatures of tens of millions of degrees and keep it confined in a state of plasma for a given amount of time which is the part that is surprisingly hard the initial heating requires a large input of energy before any fusion reactions will take place so the subsequent energy given off must be large enough to make up for this investment confining the plasma is of paramount importance and the subject of most current research because bad confinement means that the heat will leak out and more energy must be put in the simplest way to think about it is to imagine you are running a business selling apples you'll have direct costs paying the farmers transporting the goods and you'll have the overheads things like keeping the lights on literally above your head in that case the profit is a monetary one and eventually a fusion plant would have to make a dollar profit but for now let's forget the costs and money and only look at making a profit in terms of electrical energy proven technologies like coal power plants do have energy overheads such as the power needed to keep the lights on or run the hand dryers in the toilets then there are direct energy costs like lifting the coal into the furnace the electrical energy generated from each lump of coal more than covers the energy needed to mine it and move it the whole plant easily overcomes the overheads and makes a huge net gain in electricity for any kind of fusion plant this is much harder because both these types of energy costs are enormous to run any practical fusion plant we must pump electricity into a number of hungry systems things like powerful computer control systems magnetic coils and so on all fusion reactors would have to maintain a very high level of vacuum for instance which would not only require turbine blades to be spun very rapidly but also to be cooled to cryogenic temperatures there is also a direct energy cost for every gram of fuel which must be heated up which increases the worse the confinement is one big thing that fusion startups are promising is to show a fusion energy gain more energy out of your device than you put in let me show you why this is also not good enough with some very rough numbers i will use an example of a spherical tokamak which is the configuration of two of the bold claims i mentioned earlier suppose we capture 100 units of fusion energy from our reactor as heat those pesky thermodynamics from before mean i'd be lucky to turn this into 50 units of electrical energy 20 units go to the overheads the magnetic coils pumps control systems the other 30 are used for heating and current drive in the plasma suppose we only use a technique called electron cyclotron resonance heating where energy is delivered to the electrons in the plasma by microwaves the microwaves will be generated by giatrons at say 50 efficiency for a total of 15 units of energy the microwaves are transmitted through wave guides into the reactor some are lost on the way some are absorbed by the walls some are scattered or absorbed by edge plasma that will never get hot enough to undergo fusion reactions ultimately only a third of the microwaves five units of energy are absorbed in the core where they will enable fusion reactions so now we have to have a 20-fold gain on our five units of energy to get back to the 100 units of thermal energy we started with realistically we need an even higher gain still the highest sustained energy output from a magnetic device was 30 percent of the energy input at the joint european taurus and more recently at the national ignition facility the fusion output slightly exceeded the laser energy input both of these are incredible feats which took an international community many years to achieve to now go up by several orders of magnitude again in the next 9 years or even 19 years is at best overly optimistic by the way the problem with the nif is that it does one shot every few hours even if eventually electrical energy could be generated in absolute terms this is much less energy generation than the environmentally friendly approach of letting a single small goat graze on grass and walk a little bit on a treadmill now you might think that i just pulled some numbers out of my behind so let's look at a peer-reviewed article from 2016 by a team at the princeton plasma physics laboratory ppl has a proven track record in fusion research and experience running their own spherical tokamak in their article they go over all the aspects of a possible prototype plant in particular something they call the engineering gain the true output of usable electrical power for a given input the article painstakingly goes through realistic best-case estimates for the necessary power to all the relevant systems like the pumps magnetic coils and so on you can check out this article in the engineering gain formula but for now let me explain one of the figures on the x-axis is the major radius of the spherical tokamak in meters a measure of its size the larger it is the easier it is proportionately to confine the plasma and achieve gain the engineering gain is on the left y-axis with three curves corresponding to different values of the thermal efficiency this is that efficiency i mentioned of turning thermal energy into electricity we are shown curves for 0.59 or 59 in green 45 in red and 30 in blue but then we have a fourth dashed curve with a scale on the right y axis which is the fusion gain with a range up to 50. with the most optimistic 59 thermal efficiency to get above an engineering gain of 1 and therefore be making electricity we might choose a major radius of 1.8 meters for our tokamak this gets a comfortable engineering gain with a corresponding fusion gain of 19 at 45 thermal efficiency we would need to choose a major radius above 2.1 meters the engineering gain is about the same as before but the fusion gain is something like 37 so just as in my example we need a 20 30 or even 100 fold fusion gain over the input energy to have a meaningful gain in electricity it's not enough to just show again to be making electricity if you thought things were complicated so far you're not wrong this is a common bamboozling tactic that's frequently used in fusion let's suppose that we run a very unethical privately funded startup with our own spherical tokamak we have achieved a fusion gain of two over the five units of microwave energy delivered to the plasma this is already far better than what has been shown so far but we find some roadblock wherein we know that we won't be able to go any higher being unscrupulous in our press release we would completely neglect to say that we began with 50 units of electrical energy we would just say that we took five units and turn them into ten success the press and the venture capitalist would just see it as number go up even if the venture capitalists know that your reactor will never produce electricity all they need to do is use the hype to sell their shares for higher than they bought them i mentioned that the easiest fusion reaction to make work and hence the one that everyone eventually wants to use is that between the two isotopes of hydrogen deuterium and tritium deuterium occurs in seawater but tritium is radioactive and does not occur naturally fortunately each deuterium tritium reaction releases a neutron which can be absorbed by lithium on the edge of the reactor to create tritium through another nuclear reaction one tritium atom creates one neutron the neutron is absorbed to create one tritium atom this process will also have inefficiencies as the tritium decays radioactively and some neutrons will be lost fortunately there is a reaction where a neutron can strike a beryllium atom and release a second neutron thereby getting two tritium atoms for the price of one so now your commercial fusion reactor needs to not only break even on the energy but also on the tritium production or breeding plucking stupid numbers out of my behind again we start off with 100 atoms of tritium 5 decay or are lost 50 fused to produce neutrons of which 5 are also lost 45 neutrons must now produce 55 tritium atoms to get back to the 100 we started with a reactor could run indefinitely with a so-called tritium breeding ratio of about 1.15 to 1.3 this would be done by carefully engineering a thick blanket filled with beryllium and lithium all around the reaction chamber all good on paper but in practice none of the startups i mentioned have even released plans let alone work through and tested the engineering of these kinds of blankets academics including those at the uk atomic energy authority are doing some of the research and design but again none of them have been fully built let alone properly tested inside a working fusion reactor to actually absorb those neutrons coming from your fusion reactions which by the way are carrying the majority of the energy you must physically have roughly a meter of dense material around your fusion reactor because the neutrons are not charged they are not slowed down unless they interact with a nucleus directly you must therefore put enough atoms in their way to stop them when a neutron is absorbed by any element other than lithium or beryllium it will typically turn the stable nucleus into a heavier radioactive one if the phosphorus in your dna absorbs a neutron it will turn into an unstable isotope which will then decay by means of beta emission and become a sulfur atom i hope i don't need to say this but both of these things are very bad for your dna if you don't physically have enough material around your reactor for example if you claim that your reactor could fit in a shipping container you've got two big problems you are losing many of the neutrons that are carrying your fusion energy so it will be that much harder to have a gain in energy and you're making the air all around highly radioactive it is possible to do other fusion reactions but as long as it involves deuterium which is most of the other practical reactions neutrons will be given off and must be stopped to avoid making things radioactive the proton boron reaction is the only a neutronic one but it is hundreds of times harder to achieve so a high fusion gain will be that much harder thinking that the issues of neutrons and tritium breeding can be solved as an afterthought is like saying hydrogen and oxygen can power rocket now go build me a mission to mars it's just not that easy one of the main proposals inside the article from princeton was the creation of a fusion nuclear science facility this would allow the scientific and technological challenges of working with neutrons and breeding tritium to be addressed getting such a facility just to start experiments by 2040 would be a challenge however i've been very gloomy so far but for what it's worth i think there is real progress being made by some groups the international collaboration of eta is really making strides it is taking the slow but steady approach being built now and ready by 2025 is a conventional tokamak which is a tried and tested concept scaled up with things like superconducting magnets the plan is to steadily work up to a fusion gain of 10 and show continuous uninterrupted operation for up to an hour very importantly it has several test beds for lithium blankets to actually see what they would behave like in a real reactor on the other side and i must admit i'm biased towards them are mit and their spin-off commonwealth fusion systems both have that kind of lean rough and ready startup mentality but it's backed with a wealth of experience and real groundbreaking tech they have demonstrated new high-temperature superconductors which could really help push their fusion gain up and they are designing their reactor with technologies like tritium breeding blankets from the ground up also while they probably will miss some of their milestones their website doesn't have an end date that i can poke fun at thanks for listening the sources are in the description if there is enough interest i will make a follow-up video about the technical aspects of fusion such as why a fuser can never generate electricity how different reactor concepts work and details of the main challenges which i didn't have time to mention

Channel: Improbable Matter

Views: 1,471,006

Keywords: fusion, fusion power, energy, future

Id: JurplDfPi3U

Length: 15min 42sec (942 seconds)

Published: Fri Sep 10 2021

Reddit Comments

[u/BakaTensai]

Fusion has been 40 years away for what… 80 years now?

[u/OliverSparrow]

The supposed refutation of fusor energy production was unconvincing. Lithium deuteride, accelerated to an MV or so before slamming into a tungsten anode should generate fusion, and heat. To compare this to rubbing your hands together sounds facile.

He also ignores beam-beam technologies, which generate alpha particles but no neutrons. Gyrating alphas in magnetic fields produced microwaves which can be efficiently collected as electricity. The world doesn't have to be tokamak shaped.

[u/Psiweapon]

...why does this sound so much like Science and Futurism with Isaac Arthur?

Not just quite the same but like 90%

[u/pearlsandplumes]

We'll probably have it, it just won't be commercially attractive anymore by that point. Except maybe for small rich countries that don't want to import energy from elsewhere and/or use precious real estate for renewables. And how many of those are there, anyway?