New records on Wendelstein 7-X
iter.org238 points by greesil a day ago
238 points by greesil a day ago
A better link: https://www.ipp.mpg.de/5532945/w7x?c=5481737
(there is some irony in using the iter.org link for a stellarator announcement)
1.8GJ over 360 seconds, beta of 0.03
> "1.8GJ over 360 seconds"
Not sure if this is contextually obvious to practitioners, but that figure is the "Energy turnover" / "is calculated as the product of injected heating power and plasma duration".
The irony is delicious.
Especially considering the total budget of it is $340 millions vs ITER's tens of billions.
Iter and 7-X are both publicly funded research in confinement fusion with different topologies.
90% of the basic research Iter does can be switched to 7-X if it turns out to be more successful topology. Among other things, Iter develpes technologies and processes needed for a fusion power station, something 7-X is not even touching.
To be fair, they might not be totally independent figures in the sense of, I would be surprised if the cheaper project did not benefit at all from the knowledge created by the larger project.
Help on either project actually flows both ways. If I remember correctly, Wendelstein 7-X provided experience and know-how regarding microwave heating and welding large plasma vessels. In the end they're scientists and engineers and don't seem to see the other project so much as competition than a way to learn more than just with one of them.
They're both riding on the back of the past 70 years of R&D on fabrication, scientific instruments and data acquisition, and plasma physics. My point is what's the marginal research value per euro spent on one vs the other? Tokamaks are sort of a known thing. It's almost pointless to discuss now because the money is spent, but ITER has always felt to me a a very inefficient use scientific funding.
ITER is like a NASA project. Built to work from the start. Still an experiment, but if they weren't sure Q > 1 would be achieved with the design, they would shut it down.
Their findings complement and help each other, there is no irony in there
Of course they can complement each other but ITER can still be an inefficient use of science funds at the same time.
Wendelstein is a plasma research machine, not a net energy machine. There's no version at that price point which is a viable power plant - ITER is the smallest viable power plant (but you wouldn't want to run it). DEMO is it's successor which is 10x larger in terms of vacuum volume and is meant to be an actual electricity producing plant.
This article has zero quantifiable information in it aside from the duration... which has no context. Who's recordkeeping this stuff? What are the other results so far? What is the tipping point where it is net positive? how long does it need to sustain a net positive fusion reaction to produce sufficient power for grid consumption? Are there other losses (thermal generation inefficiencies) that make the target even farther than energy-in<energy-out?
Here is an actual article with some context - and a reality check that other experimental reactors in the past have sustained similar triple product for longer durations... https://www.ipp.mpg.de/5532945/w7x
>The fact that W7-X results are on a par with JET is remarkable because JET had three times the plasma volume of Wendelstein 7-X.
What's important here is that W 7-X is a stellarator, a different type of fusion reactor from almost all prior reactors (they are tokamaks), with a smaller volume than the co-record holder.
That a stellarator gets these results with a much smaller fusion volume is promising for the performance of future larger stellarators, since fusion reactors typically become more efficient as they get larger.
> from almost all prior reactors (they are tokamaks)
Tokamak and Stllerator are about equally old, 1953 vs 1954, while both types where for a period developed in secrecy behind either side of the iron curtain till end of the 1960ies where collaboration started.
IPP was founded in 1960 (by, among others, my dad) and focussed on Stllerator since then (while collaborating in JET and ITER around their tokamak projects)
Apparently stellarators only became feasible recently, mostly due to vastly improved computing power, which they need to optimize the crazy shapes (https://www.ipp.mpg.de/w7x gives an idea)
(Heard that on a podcast with two of the lead physicists/engineers working there)
Yes, they are complex and require both, complex calculation and precise manufacturing and 7x is the first one being energy-positive, but tokamaks aren't really ahead either.
NIF did it with an EVEN smaller plasma volume.
Sorry this is nice for the Wendelstein itself but they are overselling it, albeit in a way that isn't too out of the norm with academic press releases.
>What is the tipping point where it is net positive?
There are several interesting net positive tipping points depending on where you draw the boundary that energy in and energy out cross. We're still in the earlier stages of net positive where the boundary is quite small and little consideration is being given to the part of the process where electrons get pushed around in a power grid.
In any future fusion power plant, a plasma with a high triple product must be maintained for long periods.
I love vague terms like "long periods". Long compared to the Planck length? Geological time? Is the advertised 43 seconds almost there or "off by 17 orders of magnitude?"
I believe it's "for as long as the reactor is to be operating", and they contrast that with the previous longest times being less than 45 seconds.
I thought the expectation was that actually-operating fusion plants would operate in pulses rather than continuously, but I could be misremembering.
Toroidal reactors have to operate in pulses. Stellarators can be operated in steady-state (although sometimes they are pulsed to achieve higher energy).
Tokamaks can also be operated in steady-state, at least theoretically. The reason a tokamak is pulsed is due to the fact the toroidal current is driven inductively, so there is a limit to how long you can keep increasing the current in the central solenoid. However there are other methods, for example, neutral beam injection and electron cyclotron current drive. You can even exploit the bootstrap current (self-generated by collisional processes in the plasma) to obtain a near 100% non-inductive toroidal plasma (this is called "advanced tokamak" regime).
Anyway, the older generation of devices was pulsed for engineering reasons (like non-superconducting coils getting too hot). The current generation of device is solving most of these and is limited by MHD instabilities alone (neoclassical tearing modes, mostly), if we can get active control mechanism working, then will be finally approach the long-pulse or steady-state regime.
But don't you need to "refuel" now and then?
W7x has a pellet injection system now.
This is shared in the better article here: https://www.ipp.mpg.de/5532945/w7x
> During the record-setting experiment, about 90 frozen hydrogen pellets, each about a millimeter in size, were injected over 43 seconds, while powerful microwaves simultaneously heated the plasma. Precise coordination between heating and pellet injection was crucial to achieve the optimal balance between heating power and fuel supply.
Refueling is not why tokamaks are pulsed.
A smooth toroidal magnetic field cannot confine plasma. The field at the outer side (further away from axis) are spread more widely and weaker than in the inner side. In a very short time, this will cause ions to drift out of confinement at the outer side. The solution is to produce a twisted, helical field, where the field lines go in circles in both directions of the toroid simultaneously, like the stripes of a candy cane in the bend.
Different reactor designs have different solutions to this. Tokamaks use a solenoid to drive a strong toroidal current in the plasma. This, in turn, causes a poloidal magnetic field, which provides the second half of the field needed for confinement. But this only works when magnetic field of the solenoid coil is varying smoothly over time in a single direction. Eventually, you hit some limit in your ability to do that, at which point you lose your ability to confine the plasma and the pulse ends.
Stellarators do not have this issue. They get the full field geometry needed from their primary field, by twisting it around the toroid in a very complex path. The downside is that they are much more difficult to design and build.
I agree vague language in popular press is sometimes annoying.
“Off by 17 orders of magnitude” would be off by 136 billion years, so not that much for sure. Assuming you want to be able to test the plant and or maintain it once per year, 43 seconds is less than 6 orders of magnitude off. The jump was more than a full order of magnitude compared to past records, so another handful such developments and we are there.
Even 1 hour of stability with a relatively short restart period (under 5 minutes) would be fine with a battery system assuming the rest of the power plant was cheap enough to build and operate.
Nuclear already gets taken offline for several weeks for refueling, but redundancy covers such issues.
Or just two reactors staggered in operation. Power grids can already coordinate on that sort of timescale.
Any fusion reactor that produces masses of free neutrons is uneconomic, because the neutrons are ridiculously corrosive to everything they collide with. Neutron activation produces a mess of radioactive isotopes, some of which fission quickly. It doesn't take long - certainly much less than a year - before you're left with components that no longer do their jobs and are also radioactive.
This is a much less sexy problem than containment, but it's a showstopper for commercialisation. You can just about imagine an epically huge reactor with unfeasibly powerful containment fields that trap fusion in the centre of a large cloud of hydrogen, which captures neutrons to make tritium to power the reaction. But that's completely unbuildable with current tech.
Aneutronic fusion is possible, but it happens at even more extreme temperatures, which are barely theoretical at the moment.
At this point we've been chasing fusion for more than 70 years, and commercialisation is as far away as ever.
You might as well just build yourself a small star.
Or perhaps even spend all that research money on making better use of the star we already have.
General Fusion claim to get around these issues by having the fusion take place inside a centrifuge of liquid lithium. I'm not knowledgable enough to determine how plausible their claims are, though.
Looking at the picture, I wonder if complexity of these devices will significantly be reduced once it finally works. I assume a lot of the bells and whistles are needed to find the way, but once it's found..
In my experience doing plumbing/hydraulics/pneumatics for industrial equipment, the first generation of a new product always looks way more complex than later versions. But I'm not sure they're actually more complex, they're often using a smaller variety of more flexible "industrial Lego" rather than custom, unique parts that are harder to extend or modify.
Yeah, a single welded tube of the right diameter that necks down just so in that one spot to prevent cavitation, which has that sweeping multi-planar bend to just barely sneak through that obstruction, will look neat and tidy to a casual observer. Conversely, a stack of triclamp flanges, a straight length of pipe that shoots way out away from the guts of the equipment before it jogs sideways and down and back in with 90 degree couplings and gaskets and a manual shut-off valve and a pressure transmitter/flow meter and a "T" with a cap (just in case) and a sight glass looks like an awful mess.
But I can build the latter in half an hour with parts we have on hand. And I'm not even a fitter, I'm an engineer! And when you do want to add something to it, I can do that in 5 minutes. After observing it function through the full regime of pressure and flow and viscosity parameters the equipment might have to deal with, I can maybe generate a print for the real plumbers to build the former dedicated-purpose component that sets all the constraints in stone (or rather, in welded stainless). That part will be unique and inflexible, embedding all the restrictions and history and test results and design decisions into a component that looks deceptively smooth to a layman's eyes.
Is that simpler? I suppose it depends on your perspective.
W7-X looks insane because its configuration was discovered by a computer pursuing a numerical optimization. We don't have any sound reasons to believe the next one will be simpler.
> We don't have any sound reasons to believe the next one will be simpler.
Yes and no. I think you are right that the plasma shape is going to remain very complex.
But that's not the only reason why W7-X looks complicated. It has a ton of diagnostics ports on the plasma vessel just for research. Most of those we can probably design out for a production version.
So I would expect a production version of a stelarator to be simpler than W7-X, but still remain very complex.
Your question reminds me of the image showing how SpaceX raptor motors evolved https://imgur.com/a/4w3q3lS
Wow - beautiful. So there is hope! As someone unfamiliar with the challenges of mechanical engineering, I’ve often wondered at the complexity of fusion reactors. This picture puts a lot into perspective. Thanks for sharing!
To be fair, the reason the right-most Raptor looks so clean is because they moved all the piping (all the complexity) to inside the casing. And the reason they made the effort is because the casing protects the tubing from the heat of re-entry. Otherwise they'd have to waste mass on heat shielding. [Take a look at videos of Superheavy Booster returning back to the launch tower--the bottom engine sections starts to glow from the heat.]
I don't think that applies to Stellarators, so there may not be an incentive to simplify it. [But what do I know; I'm just a simple programmer.]
> the bottom engine sections starts to glow from the heat
It's fuel burning, not glow. Speed is too low for glowing; glow would start at the edge, not from deep inside the skirt etc.
Is that an actual honest photo? The first two seem fully equipped including what seems to be shielded wiring harnesses. #3 looks totally devoid of any electronics.
disclaimer: I don't follow this stuff at all. It just looks like a b.s. photo deliberately exaggerating how simplified #3 is vs. the others to this grease monkey.
IIRC not only did they remove many parts completely, but others have been integrated into the interior, which makes repair harder but will improve reliability since they are no longer exposed.
I'm not keen on the idea of applying a 'keep subtracting things until it blows up' mentality to fusion reactors.
I wouldn't be concerned about this, personally, for the precise reason that it is a fusion device - not fission!
Fusion is incredibly difficult just to start, let alone keep burning - unlike fission, which is only too happy to enter runaway conditions if not very carefully regulated. Fusion is like a little ember in your fireplace you have to carefully blow on to keep alight; fission is like keeping a fireplace lit by pouring gasoline into it.
I'd say (older-generation) fission is more like having an indoor swimming pool filled with burning gasoline, but keeping the windows shut so there's only enough air for it to burn at the rate you want to heat the house.
Or a swimming pool full of those spicy rocket propellents discussed in the book Ignition! which have combustion products like hydrogen fluoride.
Neither of the hypergolics described in Command and Control seem chill either: the fuel reacts with atmospheric water and oxygen, the oxidizer is in the highest category of poison (https://www.penguinrandomhouse.co.za/extracts/command-and-co...).
Indeed there's no such thing as a free launch, and that is rocket science.
Would love to take a look at your library.
Not the poster above, but as someone who also has a copy of Ignition! in their library, I think you might enjoy the pdf version:
https://library.sciencemadness.org/library/books/ignition.pd...
You could probably summarize the history of bridge-building as "keep subtracting things until they don't stand up anymore."
Building bridges (and large structures in general) has always been about the tension between over-engineering (for safety) and under-engineering (for cost/aesthetics).
The Brooklyn Bridge is massive; they'd never built a bridge like that so they over-engineered it. But once they saw that it was more than strong enough to stand up, the next bridge was lighter. And the next one after that was even lighter. And so on, until a bridge collapses because some new factor came into play (e.g., harmonic resonance).
Source: To Engineer Is Human by Henry Petroski--one of my favorite engineering books.
When I was an engineering summer intern at HP, they had all the interns do a side project of building a bridge (model sized). The designs would be judged by stacking bricks on the bridges and then dividing the max count of bricks before failure by the weight of the bridge. Most interns, myself included, over engineered our designs. One intern “got it” and submitted a bridge that was built out of just a few pieces of balsa wood. It only held one or two bricks before snapping, but it was ultra-light and won the competition. That exercise always stayed with me. Engineers always need to focus on the correct priorities and understand when “enough is enough.”
The nice thing about fusion reactors is that they don’t blow up but just don’t work anymore.
they have fission reactors that have done that since the 60s (CANDU Reactor). They just don't help you produce nuclear bombs...
CANDU has low intrinsic nuclear proliferation resistance. It can run on natural uranium, so it's easier to fuel than light water reactors which need enriched uranium, and its online fuel-swapping design means that it's easy to switch to low-burnup operation for generating weapons grade plutonium. Current CANDU power reactors have extensive monitoring to confirm that they are used peacefully, but if e.g. South Korea had a security crisis and decided to pursue a crash nuclear weapons program, world opinion be damned, its CANDU based reactors at Wolseong could be quickly reconfigured for weapons purposes:
It's topical that India's nuclear weapons program was started up with a Canadian-supplied heavy water reactor (though not CANDU; a not-power-generating type).
https://en.wikipedia.org/wiki/CIRUS_reactor
> "Canada stipulated, and the U.S. supply contract for the heavy water explicitly specified, that it only be used for peaceful purposes. Nonetheless, CIRUS produced some of India's initial weapons-grade plutonium stockpile,[6] as well as the plutonium for India's 1974 Pokhran-I (Codename Smiling Buddha) nuclear test, the country's first nuclear test.[7]"
You should be keen on that idea. Simpler designs are usually more reliable. And a fusion reactor doesn't really blow up. It's hard enough to make it do something.
I mean, it's expensive but there's nothing that can happen, they just stop working the nanosecond the environment isn't just right.
That's how it goes most of the time. First you have to make it work somehow, often in a very complex way. Once you have something that works, either you can strip away a lot or the components get commoditized and you can buy them in a nice package. A lot of our devices are super complex but you can build a device without much knowledge because the complexity is hidden away in nicely packaged components.
These reactors are build for research, so presumably they need to be more modular, have more measuring components and be more accessible for changes.
The real problem with fusion power is that even if they figure it out, it still won't be cost competitive with solar and wind.
Economically all the cost of building a "boil some water and turn some turbines" plant is _already_ in the "boiling some water and turning some turbines" part of the generation, and even if the heat part of it was _free_, the rest of it would be too expensive to bother building a plant for it, compared to just building solar and wind generation and some better batteries.
Batteries are nowhere near that cheap.
Currently the cheapest non-intermittent energy source is gas; solar costs about half as much, and nuclear costs 50% more than gas [0]. Battery storage is currently competitive with gas for storing around 4 hours of electricity [1].
If we would want to replace the baseload with solar + batteries we would need to store 12 hours instead, during the dark half of the day, so it would cost 3x as much, 200% more than gas.
Maybe we can hope for battery prices to drop, but extrapolating from a Wright's law curve, for them to become cheaper by a factor of 3 we need to produce 32 times as many of them [1, again], it won't happen in the near future.
[0] https://www.eia.gov/outlooks/aeo/electricity_generation/pdf/... [1] https://www.lesswrong.com/posts/mnaEgW9JgiochnES2/2024-was-t...
> real problem with fusion power is that even if they figure it out, it still won't be cost competitive with solar and wind
This is difficult to say when comparing an emerging technology with an established technology in an emerging economy.
Based on every historical prior, it would be surprising if there weren't diminishing returns to solar and wind. And I wouldn't underestimate the degree to which power is, in part, fashion. Today we value emissions. Tomorrow it may be preserving and expanding wild spaces.
On a practical level, fusion research doesn't compete with solar and wind deployment. Pursuing both is optimal.
PV Panel production acts more like typical mass production and has therefore much higher cost benefits compared to every other way of producing power.
For every other way of producing energy you need separate land for PV you don't. You can put them on rooftops, over parking lots or even vertical in a field. The last one increases the crop yield. Crops get less harsh sun, lose less water and the evaporation cools down the panels, which increases their production.
Today we value costs of energy production and tomorrow we will to. Especially if it results in energy independence. You don't need to buy fuel for PV and wind. As with nuclear fuel only a few countries are probably going to manufacturing the fuel needed for fusion reactors. Producing enough of it and in a sufficient purity needs specialized facilities and they will only be profitable if they produce a lot of it.
> PV Panel production acts more like typical mass production and has therefore much higher cost benefits compared to every other way of producing power
Turbines are also mass manufactured. (Albeit less than PVs.)
> You can put them on rooftops, over parking lots or even vertical in a field
The first power plant burned coal in Manhattan [1]. You can put turbines on top of buildings. We don’t because we don’t want to.
I think wind turbines are pretty. But lots of people don’t, and many wouldn’t want their rooftops to be shaded by panels, or wide open fields and natural expanses turned into something that looks more industrial. (I personally think looking down on rooftop gardens is far prettier than panels.)
Maybe there is a perfect power source out there, one which justifies a monoculture. I haven't seen it. I don't believe it's solar or wind.
Additionally, the total amount of solar and wind is limited. Surely more than we need now, don't get me wrong, but how much more? Factor 2? 10? I could see a future that is extremely energy hungry, and not just because of AI.
> the total amount of solar and wind is limited
I'd be shocked if we max out on insolation before area we're willing to cover with solar panels and windmills.
True if you look at the cost to build the plant, but it’s hard to colocate enough solar with heavy users, land near there is expensive, and transmission capacity is pretty hard to get built, so something very power dense with a small footprint is helpful. I haven’t dug into the numbers, so I could very well be wrong that it pencils out when you consider those.
And there are efforts to make building out transmission and interconnecting with the grid more streamlined, so maybe some of those problems will be gone by the time fusion’s ready.
Someone said recently that it’s nicer to have bad laws and good tech than a bad tech and good laws, solar+storage seems like it’s in the former now, and if we can clear the bureaucratic hurdles, we’ll see it boom here like we’ve seen elsewhere.
This completely ignores the need for baseload generation. Wind and solar will probably always be cheaper, but the power grid will likely always need a diverse array of power supplies. If your photovalic cell factories get bombed, how will you make more? If Egypt were 100% solar powered, it would be trivial to defeat them in a war by shooting less than a million dollars of artillery shells into their solar plants, leaving everyone in the dark in perpetuity. Japan was almost wholly dependent on the US for oil and coal before the US pulled their delivery contracts which was partly why they bombed pearl harbor, they had little to no power diversity. Nuclear and hydro will always backstop grid energy, even if solar becomes free or net negative.
The article links to the original source, which has more details:
Does it kill the idea of a tokamak as an energy production device? As in a stellarator proving the much more promising design...
Not an expert on the topic by any means, but IIRC:
- Those designs have been in parallel R&D for decades
- Tokamaks are conceptually simpler, thus might be easier/faster/cheaper to make into viable installations
- Stellarators are WAAAAAY more complex to design and build but AFAIU they would have the huge benefit of being able to sustain the plasma for way longer for the same "startup cost" of a cycle since the particles of the plasma are routed somewhat like they're on a mobius strip instead of a simple torus (which should make it easier to confine more particles for a longer time).
I recall having read (several years ago) that the simulation technology of the 90's wasn't really up to the task of aiding in the design of those weird wavy magnets for Wendelstein 7-X, an unfortunate reality which delayed the project a lot.
Both ideas are pretty old (50s) and in development for a long time. Both designs have their pros and cons. The biggest drawback of the Tokamak however is that it can only be pulsed... which is kind of dumb to actually generate and provide energy in the long run. You really want the Stellarator here, since there it is at least theoretically possible to run "for ever" (not entirely true, but long enough cycles to be used in a power plant).
There are 2 podcast episodes with the guys who run Wendelstein here: http://www.alternativlos.org/51/ (it's German tho)
These podcasts are really good. I remember the part where they had problems with some screws and the simple solution was to coat them with diamond.
Tokamaks are conceptually elegant but contain significant inefficiencies which negatively impact potential net power output. Both tokamaks and optimized stellarators have magnetic fields possessing omnigeneity [1], but tokamaks require two magnetic fields (poloidal and toroidal) whereas stellarators employ one.
The bigger question is if magnetic confinement fusion will lead to the best energy producing devices. Competitors include inertial confinement, pinches, or some other exotic method. If a magnetic confinement fusion device produces net power, it's going to be a stellarator.
Sources:
Maybe, maybe not. There are dozens of unsolved problems to get to commercial fusion. For a lot of the problems, to solve them it doesn't matter if it's a stellarator or tokamak.
I would also be super careful about celebrating new designs as the way forward that will replace everything. When you look at the history of combustion engines we had a ton of new approaches (for example rotary engines) but after looking at all factors it turned that evolutionary changes to existing designs was the way forward.
Perhaps, unless you fall prey to the sunk cost fallacy and have already spent a bazillion dollars on generations of tokamaks!
I've always been somewhat partial to the stellarator design, I mean a big plasma donut is cool and all, but what if we twisted it around a whole bunch first!?
I think gravitational confinement is the way to go - it's the only operationally proven design!
Gotta think big!
No, it's not the only proven design. The other is a hydrogen bomb. Google project PACER.
True - inertial confinement - also used by NIF (laser based). I guess I should have said continuous operation, although I do like the simplicity of Helion's system.
It has density issues though. If you had a piece of the sun the size of a huge power plant - like enormous, the power output would be too low to be useful.
Mandatory: We should build it in space and beam the electricity back to earth using electromagnetic waves. We could collect those using solar cells. And then get rid of the plant and use the sun instead.
Yes - exactly. No need for a Dyson sphere, or a man-made sun - just use the real sun and solar panels!
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Old article, from June...don't get me excited
TL;DR - Looks dangerous, but is it? (open question) Can we quantify it or at least make it more tangible?
God, this contraption appears to be the kind of thing I wouldn’t trust my life with. Every time I look at a fusion reactor, it seems far more dangerous than my hobby lab, failing to inspire any confidence. The numerous moving parts create an equal number of potential points of failure. In contrast, a nuclear reactor doesn’t have to contend with plasma gases hotter than the Sun, contained within an artificial bubble solely through the assistance of electromagnetic radiation.
I’ve often tried to imagine the worst case scenario, but I am limited by my knowledge on the subject. What kind of damage can hot plasma at a few million degree C do?
On one hand, the plasma is hotter than anything on earth created by mankind. Then I believe there’s also a significant number of wild neutrons shooting around which can cause havoc in their own right, if not contained. But on the other hand, unlike an uncontrolled chain reaction, without a source of heat, the whole operation shuts off by itself. I’m probably wrong about a few assumptions here but this is what I often find myself wondering.
I'd imagine that these research reactors are chock full of "adjustable parameter" parts and modular assemblies.
Once they get everything dialed in, they can make a static purpose built machine with dramatically less complexity. Generally with research machines they are very unwieldy while still being dialed in.
That fusion reactions are so difficult to get started makes the reactors very safe because failure makes them stop. So, if you lose magnetic confinement the reaction stops. The reactor may be damaged but that's it.
This is unlike fission reactors, where a failure causes reactivity to increase. That causes meltdown and the possibility of explosion and all the nasty radioactive contamination.
My understanding is that more recent fission reactor designs are done in such a way that they fail in ways which cause the reaction to diminish rather than build up further, which puts you in a better place than, say, Chernobyl.
You still have a very hot very radioactive lump of death in the middle of your busted reactor when it's all done though, and that's definitely not fun. Fusion failure modes - in current designs anyway - are far more appealing to anybody who happens to be in the area at the time.