Can someone explain to a lay person what they accomplished and what it means for nuclear fusion as an energy source?
Before you get cosmic energy out of nuclear fusion fuel (usually isotopes of hydrogen), you have to put a bunch of energy into the fuel to get it into fusion conditions. Namely, you have to heat it up and compress it so the nuclei get close enough to fuse (after which they'll release energy).
There are a few milestones along the way to commercial fusion energy:
* Get more energy out of a fusion fuel than you put into it
* Get more energy out of fusion fuel that it took you to make the energy you put into it
* Build a way to capture the net gain energy and convert it into electricity
* Demonstrate the integrated power plant as a prototype system
* Build and operate the first commercial power plant
* Assuming good economic and technical performance, start building a fleet
* Deal with fleet scaling issues
* Profit!
This is a celebration of the first bullet.
a) ruled out by the laws of physics, or
b) possible.
Commercial ICF is in the latter category as far as I can tell.
In other words, maybe?
AFAIK energy generation with ICF is much closer to the latter than the former.
- Will Capx be lower compared to a advanced fission plant. Almost certainty not.
- Will Fusion plan be significantly cheaper to fuel. Almost certainty not, uranium and thorium are available in waste quantities.
- Will it solve proliferation concerns? No, if you have a control of a fission reactors you have the potential to do all sorts of things.
- Will it solve the nuclear waste issue. Maybe slightly but advanced fission can produce waste that need to be stored for around 300 years and that is not actually that difficult.
And that is of course if you assume that the 100s of billions in investment required will not have be be paid back in any way. That is partly fair because fission didn't have to do that either, but there the investment is shared with nuclear weapons (for better or worse).
So I would say its closer to the second suggestion. I don't see a theoretical path of how a fusion reactor can be built cheaper then a comparable fission reactor.
But I'm not a expert on fission, I have heard of some fission that could be built very small but all actual real designs for suggestion of commercial fission I have seen do not fall into that category.
Also: "Here at SpaceX we specialize in turning the impossible into just late".
b) is two things
b1) possible and worth the cost
b2) merely possible
x) require preexisting conditions not present in the Universe, or
I don’t know why their plan is to just vent helium given the shortage although I imagine that’s a second order problem they can solve later.
And then compare to that the very complex and expensive process of process of breeding tritium.
How does that make any sense?
Sure, fusion is about 3 order of magnitude denser, but fission is already incredibly dense. The increase density doesn't really benefit you in any practical way unless maybe if you are trying to do interstellar flight or something.
Maybe the Belters will mine lithium from asteroids and send them back to earth in exchange for air and water...
At one point back in the 1960s some physicists were trying to make a neutron detector using lithium, and it wouldn't work. They eventually discovered the lithium they had purchased from a chemical supply company was nearly pure 7Li. It had been sold back into the chemical market from the waste stream of the government's lithium enrichment facility.
This result does not bring us any nearer to civil energy production via fusion.
It clearly does not. I can understand the researchers feeling unable to tell the press, "Look, this is just basic research. Like the JWST." It might lead to a massive reaction that "well, then you have to just get in line for those basic research dollars, instead of being a top-priority thing we throw money at."
All those research dollars they'd be giving up!
However, ITER is a global effort, so it isn't just the US budgets we have to consider, right?
Would you mind answering a layman's question on where the energy comes from in fusion: my understanding is that the problem here is that energy has to be put in to overcome electromagnetic repulsion between atom nuclei so that the strong force can take over and combine them into a new nuclei, releasing energy at that time.
Is this interpretation correct-ish?
I vaguely recall reading a long time back that managing the emanating free neutrons was also a challenge. Has that been solved?
Its successor, ITER is supposed to produce more energy than used in creating the fusion process. It is still under construction in France.
Still a very long way to go before becoming similar to a fossil burning power plant. They got equivalent of 1 megawatt for a single second. A typical coal plant is hundreds of megawatts continuously.
What does that mean if the cost of energy is 0 ? (e.g renewables)
While renewables are making increasingly cheap generators, the overall systems involved in delivering reliable energy from them are increasingly expensive at increasing scale. Check energy costs to customers e.g. in Germany.
Mining, energy storage, transmission, demand control, recycling, maintenance, land rights, etc. for any energy source at world scale will continue to cost well >$0. For nuclear fission, fuel cost is only 5% of the total cost. For renewables, fuel cost is 0%, but that doesn't mean there aren't costs.
During those times, in some parts of Europe for example, renewable energy really is practically free. This is a problem for nuclear and fossil plants which lose money during those times. The renewable operators don't make much either but at least they don't have very high input costs.
Not merely "practically free", but actually negative price. i.e. they pay you to use electricity, because they need to get rid of it.
https://www.energycouncil.com.au/analysis/increases-in-negat...
Isn’t it more fair to say that during those times they are resting their costs at a higher rate than with their typical output?
Please better check France for the often touted right way of going nucelar, with half of their overaged reactors taken off the grid due to failing safety regulations (which are not too hard but have been dangerously softened over ye years..), cracks and corrosion problems, and their unfolding catastrophe in regard to nonavailable cooling fluid, which is a problem that will only become much bigger in the future years.
Also don't distract and mix energy with energy, if something we have a heating and fuel problem, not electeicity. Secondly our gas reservoirs are already 75% filled again ahead of plan surprise surprise.. seems the lasts months panic had a little bit too much agenda involved.
If you ask me energy prices here are still much too low for what is upcoming and humanity should really focus on... this will make current debates so absurd and laughable, not getting it.
Why not look at some other examples who fully went renewables and doing it succesfully? Stop looking at a wanted or at least easily prevented politic, lobbyism and incompetence failure, that now leads to prices that are still much too cheap for what our wastage of resources should actually cost, lol.
But if you do 100% wind and solar, then you have to start spending money on things other than generators. The fraction of cost that is wind/solar generators vs. e.g. energy storage systems, transmission, recycling, etc. shifts from 1 to ~0 at scale.
This is handwaving away the most difficult part of of a 100% renewable grid.
This is a colossal amount of storage, far outside the bounds of existing storage methods. Hence why plans for a renewable grid assume untested mechanisms like power to gas or compressed air will just scale to near-infinity.
Most existing storage, taking advantage of existing hydro-power dams, uses excess energy to force water up to the reservoir, which energy is later extracted by letting it flow out through a turbine. New pumped-hydro systems built just for storage will be radically cheaper than existing dams, and be practical in hundreds of times as many places: you just need a hilltop no one is using, and water to pump up to it. The reservoir may be much cheaper than a hydro power dam because it does not need to contain high pressure; an earthen dike suffices.
There are numerous other, equally simple methods, for places without enough hills or water. Synthetic fuels like hydrogen and ammonia are an attractive choice because tankage is cheap, and they are transportable and have myriad industrial uses, so after your tankage is full you can sell all further production.
Of course one only builds storage after there is excess energy to put in it. We will need a lot of it, in time, but it is all just construction and mechanics: ordinary civil engineering.
(If you have to lie about the practicality of storage in order to promote nukes, what does that really tell us about your nukes?)
You're right that hydroelectric offers lots of storage potential. But it's geographically limited. Great for countries like Norway that have lots of it. But countries that don't can't just summon dam-able mountain valleys.
You need more than just a hilltop to build pumped hydro. You need a hilltop, with access to a water source. It also needs to be close to a transportation network otherwise construction costs will be prohibitively expensive. Pumped hydro plants do indeed cost a lot: the biggest one in the US in Bath County cost $4 billion dollars for a capacity of 24 GWh.
Furthermore, it will get more expensive as it scales up: as the most accessible sites are developed, subsequent facilities have to be built in more and more suboptimal sites.
> The reservoir may be much cheaper than a hydro power dam because it does not need to contain high pressure; an earthen dike suffices
This makes absolutely no sense. I needs high pressure to generate electricity. Low pressure would mean there's hardly any potential energy to tap. If you're suggesting we have a tunnel leading out from under the reservoir, then those have to be built in exactly the right geography where there's an alpine lake with a height difference.
> There are numerous other, equally simple methods, for places without enough hills or water.
Yet, despite these methods purported simplicity you didn't actually specify them (Edit: you added a couple in an edit after I typed my reply). Because then you'd have to defend their viability.
Since you edited in hydrogen and ammonia:
* Power to hydrogen: electrolysis of water remains expensive, hence why most hydrogen is built with steam reformation. It's not just the electricity costs, but also maintaining the electrodes that perform the hydrolysis.
* Power to Ammonia: this needs a source of hydrogen, so it shares all of the above's issues. Ammonia is really just a storage mechanism for hydrogen, actually producing usable energy from ammonia is done by releasing the hydrogen from the ammonia and then running it through a fuel cell.
You're the one being overly optimistic about the practicality of storage. We've had excess production during peak renewable generation for close to a decade now. The excuse that we won't build storage until there's an excess of electricity isn't valid. Places like Hawaii and California already are saturating the energy market, but the storage is systems you propose aren't being built because they aren't feasible.
Intermittent sources are fine to chip away at fossil fuel use, or in places with widespread hydroelectric power. But we can't kid ourselves into thinking that storage will make it feasible every. Grid scale energy storage should be approached like fusion: maybe it'll be invented and change the energy landscape. But it's foolish to treat that possibility as a given.
Pumped hydro storage does not, as I already pointed out, require river valleys. It does not, in fact, need those other things. You make clear that you know nothing about, even, pumped storage. (Maybe look up the word "penstock"?) Why would anyone trust you about others?
People often badly overspend on civil projects, but that does not give you honest numbers -- if indeed what you want is honest numbers. You make very clear that you do not want honest numbers.
Pretending that fuel synthesis depends on access to scarce raw materials (hydrogen, nitrogen? Really?) will not fool anyone. Neither will anyone be fooled by your insistence that its energy must be extracted via fuel cells.
I'm not a civil engineer, nor any kind of expert in grid-scale energy storage, so I can only note that in my amateur readings I've seen many different people (alleged experts) say the same things that Manuel_D is saying. That doesn't mean it's true, that's not my point. My point is that if you know something that all these other commentators don't, I and others would greatly appreciate it if you would explain that. But you'd need to actually explain it, not just accuse others of bad faith.
All do acknowledge that building out storage will be a project of a scale similar to that of building out renewables. Only the most dishonest would insist that the relatively small amount of storage already built demonstrates anything other than that capital is overwhelmingly better used, today, to build out new generating capacity. It would be obviously stupid to spend on building storage you have not generating capacity to charge up.
I'm well aware of what a penstock is. This [1] graphic shows how a penstock functions in pumped hydro storage. You see that "upper reservoir"? That's an alpine lake that forms the body of water that flows down through the penstock and drives the electric turbine.
You have to have the right geography to form that upper reservoir. If you tried to build a pumped hydro storage in Nebraska, you'd have to move massive amounts of earth to build that upper reservoir - essentially building an artificial alpine lake. This is prohibitively expensive to do, which is why hydroelectric storage is geographically limited.
> Pretending that fuel synthesis depends on access to scarce raw materials (hydrogen, nitrogen? Really?)
Hydrogen is almost entirely produced through steam reformation, which emits carbon dioxide. Effective hydrogen electrolysis needs expensive materials like titanium electrodes.
1. https://www.energy.gov/sites/default/files/styles/full_artic...
The graphic does not, in fact, portray an "alpine lake". It says, exactly, "Upper Reservoir". Did you hope people would not click through and see?
The place where water in the system is at high pressure is not in the upper reservoir, but only lower down, inside the penstock. Which you now claim you already knew, after lying about it.
> You see that "upper reservoir"? That's an alpine lake that forms the body of water that flows down through the penstock and drives the electric turbine.
The pressure is at the bottom of the penstock at the turbine. I'm not sure how you came to the conclusion that I wrote otherwise.
If the upper reservoir isn't raised - as in, an alpine lake - the there's no pressure in the penstock. Look at any picture of a hydroelectric storage facility:
https://i0.wp.com/esbarchives.ie/wp-content/uploads/2016/02/...
https://www.ecogeneration.com.au/wp-content/uploads/2016/12/...
https://i1.wp.com/www.cleanfuture.co.in/wp-content/uploads/2...
If the upper reservoir isn't raised well above the river or lower reservoir, then there's no pressure to drive the turbines. If you didn't build the upper reservoir up high on a mountain forming an alpine lake, and instead built it on flat ground you'd just have a big useless pond. This is why geography is crucial for pumped hydroelectricity storage.
Pumped hydro requires an elevated reservoir ("news at 11!"). It does not, in fact, require an alpine lake. Nor does the upper reservoir need concrete construction, as the pressure on its dike, if in fact one is needed at all, is limited to the depth of the water in it.
You knew all of the above, but chose to lie about it.
What pumped hydro(+other storage)+renewables is cheaper than is nuclear. You will notice Vietnam isn't building nukes either.
6000 cycles
this is 2.3 cents per kwh for storage.
Where is the handwaving?
For this reason, the costs of recent battery storage has risen considerably. Recent storage projects ended up paying $567/Kwh : https://www.utilitydive.com/news/new-york-battery-storage-co...
This is the scaling problem: if you try to deploy batteries at scales relevant to the energy grid you outstrip the supply of inputs. In order to keep up with demand, extraction industries have to tap more and more inaccessible reserves thus driving up costs. Remember, global electricity usage is 60 TWh per day. And that's just electricity, total energy use is about twice that at 120 TWh per day. Even just 12 hours of storage is hundreds of times the annual battery output - most of which isn't going to grid storage but rather electric vehicles.
That's a pretty hilarious claim given the absurd amount of global investment in the last 30 years.
And lets be real here, nuclear has actually been blocked far more then renewables. In 1982 a green activists literally shot a french nuclear reactor with RPGs. Activists have surrounded nuclear plant and prevented them from being built, only for the state to build a coal plant in the same location. Research projects were canceled as soon as they hit slight issues because politicians did not want to stick their neck out.
Compare this with renewables despite 20 decades of green transition and huge cost in Germany the results are not that great. France in 2 decades basically turned its whole gird green, Germany in comparison is not very close and still operates waste coal plants.
Even project that were actually very successful and did show path for the future had to be killed of as was the case in France:
> A 1998 "Inquiry commission on Superphenix and fast neutrons reactor sector" [3] reported that "decision to close Superphénix was included in Jospin's program ... in the agreement between Socialist Party and Green Party". Also the same report says "despite many difficulties, the technical results are meaningful". In the explanation of vote at the end of the report, commission members says "give up on Superphenix has been a big error" and "Superphenix has to die because is a symbol".
France could have build multiple more of these, but of course instead of that they are building the same old PWRs.
And generally the transition to nuclear would have happened in the US for example if coal had not been cheaper. Just as the transition to renewables had not happened without the state pushing the technology. The difference is just that now states are willing to accept higher prices and higher spending to push the preferred technology and in the 70/80s that was a total non-starter.
> Please better check France for the often touted right way of going nucelar
You mean the country that had a essentially green grid for the last 40 years? Are you aware of the fact that CO2 not produced earlier is far better for the environment then CO2 not produced now?
Because the reality is France has done the whole world a major favor by running a large industrial economy with nuclear. The real failure in France is that they didn't double down on next generation nuclear and instead simply gave up and essentially stopped adding new capacity and instead relying on gas and German coal.
Had Germany gone with nuclear the way France did both Germany and the world we would be in a much better position now. The health effects of coal in Germany alone are staggering. And that doesn't just go for Germany, German coal ash is distributed overall all of Europe, including low countries, France and Switzerland.
So to say 'look France has a few issues with nuclear now what a failure of a strategy' is ridiculous when the country next to it burns huge amount of coal and gas.
The reality is, had the world moved to nuclear we wouldn't nearly have the problem we have now. The grid would be much greener both in terms of CO2 and other emissions. Based on that you also have a great strategy to push out carbon from home heating and replacing it with electric. The same goes for home cocking with gas.
Even for Deep Decarbonization of industry and transport nuclear provides solution. High temperature nuclear heat can be used to make hydrogen or provide heat for all kinds of other chemical process that currently use gas.
We could have even done things like moving to nuclear power synthetic fuel production and added increasingly more methanol into gas (this technology was available in the form of Flex-Fuel Vehicles and has been used in the US and Brazil for example). That would have been a way to reduce carbon emission in transportation before electric cars became possible (thanks to Li-Ion). These are all things that nuclear visionaries like Alvin Weinberg advocated and that would have been possible had we pushed forward nuclear technology.
Now non of it is to say that renewable now are bad, and since we have done the investment renewable are cheap and often make more sense then nuclear (given nuclear progress has been very limited). However to claim that the nuclear strategy was the wrong one is absurd given both the CO2 output and the general emissions produced by country that didn't have a strong nuclear strategy. The world made a huge mistake by not embracing nuclear.
Therefore, providing energy, no matter the source, always has a cost.
Anyway, the cost of energy with solar / wind is obviously not 0. You have to produce the panels / windmills, perform maintenance, for solar you need to clean, etc. Additionally, the energy isn’t available always so you need energy reserves like batteries, pumped water, etc to store it for use which increases the cost further. Finally, there are energy demands that solar / windmills can’t meet where you need *really* hot temperatures.
That’s why fission repeatedly is shown as the only solution to reduce dependence on fossil fuels. Fusion is great but we should be building insane amounts of nuclear reactors right now to meaningfully decarbonize our energy generation.
* EDIT: Here’s a talk [1] by Michel Laverne CSO of General Fusion. He starts talking at the ~6 minute mark and explains why renewables will never see more than 10-20% market penetration.
...and yet market penetration of wind and solar in the UK was 26.4% in July[0] and still climbing as we build more offshore wind. Plus 1.3% hydro (and 5.9% biomass if you count that as renewable).
[0]: https://www.nationalgrideso.com/electricity-explained/electr...
There’s simply not enough battery capacity and physical land in the world for solar power plants and wind turbines to provide all the energy. Everyone always does the solar calculations ignoring the fact that energy has to be produced semi locally to where it’s used (long distance transmission is expensive and lossy). Additionally the calculations for energy capacity of renewables ignores the fact that energy that the capacity can’t be shifted to match load (without batteries).
Seriously. This is why the fossil fuel industry loves solar and wind. They’re not a serious enough threat to their business.
> We expect renewable sources will provide 22% of U.S. generation in 2022 and 24% in 2023, up from 20% in 2021.
https://www.eia.gov/outlooks/steo/report/electricity.php
> Everyone always does the solar calculations ignoring the fact that energy has to be produced semi locally to where it’s used (long distance transmission is expensive and lossy).
This is untrue. They are building a solar farm in Australia to export electricity to Singapore 3,100 miles (5,000 km) away.
https://newatlas.com/energy/sun-cable-australia-singapore-so...
In China they already have multiple operating transmission lines over 2000km.
https://en.wikipedia.org/wiki/Ultra-high-voltage_electricity...
The term "renewable" is such a poor word for 'long-term sustainable'. I wish we had something that didn't make everyone think we were violating the laws of energy conservation.
You know what was renewable, using whale oil. That's very renewable in fact, but somehow most people are against running the global economy on whale oil.
Fission is incredibly sustainable in the long term. In fact, even if we mined all the easily expressible thorium volcanic activity actually continuously brings up more.
What on earth does this mean?
Most (all?) industrial processes using electrical furnaces which work fine with renewables.
It keeps hot-neutron physicists, who you must recruit from among for weapons work, busy.
It provides continual practical challenges to plasma fluid dynamics physicists, who otherwise have great difficulty funding experiments.
It provides cash flow to the (chiefly) military contractors who build the test apparatus.
In this particular case, it lets you conduct tests for thermonuclear weapons concepts paid for out of a different budget.
Any expectation of ever getting useful energy out would be the worst reason, because there will never be one solitary erg of that.
Well, only insofar as we have all the required elements on earth. You still have to go threw a considerably complex and expensive process to make that fuel.
You need to mine lithium and then expose it to plasma to breed tritium.
> A fusion core is naturally fail safe since energy and fuel need to be constantly applied
With a breeder reactor that can be consciously refueled you can also keep its access reactivity very low. And even better, if its fuel is a molten salt the dangerous elements are chemically bound in the fuel. So even if an explosion (terrorist planting C4) would happen in the power plant, and fuel would get spread but the dangerous elements would remain in the molten salt. The dangerous elements are never gaseous and thus never leave the safety boundary of the plant.
A fission reactor in comparsion when hit by C4 can actually release gaseous radioactive material. Just not very much.
So I am not saying fusion reactors are unsafe, but rather then fission reactors can be incredibly as safe.
For myself I would much rather sleep next to a molten salt breeder reactor rather then fusion reactor.
And if there were, this would not contribute to its development.
Fuel for such a plant (tritium) is practically non-existent. What of it that exists is synthesized at great expense.
As with fission, most of the operating costs would have nothing to do with buying fuel. Solar and wind power suffer none of these costs, so fusion, like fission, would be wholly unable to produce power at a price anyone would pay without being forced to.
The fission plants still operating will find themselves increasingly unable to produce power at a price anyone will pay, so will be mothballed long short of their design life.
And, who do you imagine you are fooling?
Regarding Diablo Canyon nuclear plant: “The plant produces electricity for about 6 cents per kWh, less than the average cost of 10.1 cents per kWh that PG&E paid for electricity from other suppliers in 2014.” https://en.m.wikipedia.org/wiki/Diablo_Canyon_Power_Plant#:~....
Fusion rocket information:
https://en.wikipedia.org/wiki/Fusion_rocket
https://www.iter.org/newsline/-/3303
http://www.projectrho.com/public_html/rocket/realdesignsfusi...
A supplement to a fusion power plant: https://en.wikipedia.org/wiki/Variable_Specific_Impulse_Magn...
http://toughsf.blogspot.com/2019/10/the-expanses-epstein-dri...
The only fuels that could achieve better energy density than fusion fuel would be antimatter, or maybe some fanciful sci-fi thing we may discover down the line, such as quark fusion ( https://www.sciencealert.com/new-quark-fusion-releases-signi... ) or subatomic compression ( a concept from fiction that involves packing an immense amount of solid electrons together so tightly that the electrostatic repulsion functions as a compressed spring (perhaps using mutual gravitation almost but not quite strong enough to be a black hole as a way of preventing disastrous spontaneous decompression) ).
That doesn't cost $0. It probably costs billions of dollars.
> Sounds a bit like a nuclear reactor.
They are nuclear reactors. Nuclear fusion reactors, rather than nuclear fission reactors.
Fusion reactors and conventional nuclear (fission) reactors are very different. Only poorly designed fission reactors can meltdown and release large amounts of highly radioactive material into the environment. And no nuclear power reactor of any kind can explode into a giant fireball like a nuclear bomb; that only happens on TV shows.
That would be what they might call an "expensive setback".
They need a great deal of 6Li/7Li in the path of the neutrons to breed fuel. How they would extract small PPB concentration of volatiles is unclear.
A lithium hydride breach would be no picnic, either.
On other hand amounts used are relatively minor so it isn't massively bad issue.
The failure mode for a regular (fission) reactor can be twofold. The better scenario is that by some kind of mechanical failure the radioactive materials escape the confinement, and instead of putting their energy into the electricity generation mechanisms, just start shooting it around, irradiating things, thus breaking them (including living organism's cells and DNA) and causing them to become secondary sources of radiation. The worse scenario is that that before that, radioactive materials become too close together, starting self-sustaining chain reaction, which outputs immense amounts of energy (essentially, like a nuclear bomb), inevitably leading to destruction of whatever container it is in (no container can survive it for long, too much energy) and spreading around, by which time we're back to the scenario above (since once the materials have spread around, the chain reaction would stop) only with much more material which is much more energetic and thus will spread around wider and do more mess.
The failure mode of fusion reactor, if it happens, would be different, since it does not contain fissile material. Instead, it contains some light elements (usually the mix of deuterium and tritium, both of which are just hydrogen with some extra neutrons) which are heated and compressed a lot to start forming helium. If something breaks, the elements would not have anything to contain them (since, unlike what happens in the Sun, they don't have nearly enough gravity in themselves to be able to counter the thermal forces taking them apart) so what you'd get is a lot of very hot gases (mostly hydrogen) flying around. It's no fun, especially given hydrogen likes to explosively combine with oxygen in the air under the right conditions, but there would be no radiation involved, and it won't be able to "fuse" with anything else because it won't have enough energy to initiate the fusion process (that why we needed to compress and heat it up in the first place). So if everything goes very wrong - which is not very likely, but we're assuming the absolutely worst case scenario - we will have an explosion but noting like fission reactor. The containment is absolutely necessary - at least in current fission reactors - to achieve more energy out than in - and if it fails, the energy output will stop. This is one of the reasons fusion reactors are supposed to be safer.
There still could be some radioactive contamination involved due to fusion causing neutrons to fly around, hit the surrounding materials and turn them radioactive, and these could be spread around by the explosion, but less than in the fission case.
Now you may ask how hydrogen bombs are so destructive then? The big difference they use a regular nuke to ignite the reaction. Unless somebody builds a fusion reactor inside an exploding nuke, that's not the scenario we'll be dealing with in the fusion reactor case.
In Spiderman 2 Doc Oct is blowing stuff up with fusion.
Those are the two that pop into my head.
The problem is that the fuel mass that undergoes fusion has a lot of mechanisms for energy loss, which mean that you need to continously apply a lot of energy into the system to keep it going.
"Ignition" refers to achieving conditions where the energy output of fusion matches the energy loss from the hot spot. In this situation, it is no longer necessary to feed in energy to keep the reaction going, so long as there is sufficient fuel.