How big of an explosion can you make with a fusion reactor?

Question

The Story

This is one of three questions set in the exact same place, so bear with me here. Twenty years after the fall of the State and the Overseers, about thirty since the phase-gate to Ilus was opened, we follow a technician who is hired by the Sequoia R&D Alliance to work at this lab, Kitsuki. (Mostly as a chance to get away from the political mess that is earth after the fall.)

The inciting event is a malfunction of the fusion reactor, which eventually turns out to be sabotage, and frees the Typhon and Kit infected with a retrovirus that is part of the Keidran genetics program. And gets turned fluffy.

The Question

As a generalization, how good would fusion reactor be as a bomb? If you were to watch the TV incarnation of The Expanse, you'd be surprised by the bang the Donnager made when Yao scuttled it. Is that even close to realistic? I would assume that no, you need a proper bomb to make a proper explosion.

But as a generalization, looking at what a possible future ICF reactor does and how, could you even try to weaponize or sabotage it? Or should the saboteurs of the labs enormous power source (for the massive amount of quantum computers) be better off just getting a nuclear warhead down there and blowing the place the old fashion way.

Basically, if I wanted a boom, what do I do.

Answer 1

Not significantly more than the reactor was designed to release in normal operation.

You mention ICF reactor, so I'm assuming you are referring to inertial confinement fusion reactors - an upgrade of the Lawrence Livermore National Ignition Facility that's been in the news for the first over unity fusion reactor.

Something like this is a very complex engineered solution. The facility is supposed to be 3.5 billion USD, and the output of the event was about 3 MJ (enough energy to boil 14 kettles of water). 1 Kg TNT releases about 4.1 MJ so, not much of an explosion as clearly the machine would necessarily be designed to handle such events frequently for a long time to be a practical reactor.

So you want a much bigger bang, there are only 2 possibilities 1) you increase the yield dramatically, 2) you implode a much larger pellet.

1. Increasing the yield dramatically won't be possible to rig a much larger bang - if you knew how to do that, you would already have incorporated that in your design. Also your future ICF reactor would not be practical if the yield could be increased by orders of magnitude even with a magical 100% yield.

2. A much bigger pellet. This won't even ignite (maybe a fizzle if your lucky and achieve some fusion). Your complex reactor simply won't be able to heat a much larger pellet fast enough to reach ignition.

Suppose you decide to use a pellet 5 times the diameter of the production pellet in the hope of achieve a bang 125 times normal. The surface area of the pellet will be 25 times the standard. There is absolutely no possibility that a practical design could be over-driven sufficiently to trigger fusion event that would require 25 times the normal energy input.

Controlled fusion is a very non-linear process, you need a sufficient combination of density, temperature and confinement time to achieve. Missing target conditions means yield drops dramatically.

Also note that making a practical ICF reactor would require major improvements to the event reported on 2022 Dec 13. Such as improving the cycle time for once per day to something like once per second (or faster), and the fact that the net energy loss was roughly 100:1 as the over unity figure was based on the amount of energy delivered to the pellet - not the total energy required to deliver energy to the pellet.

But, for a story - maybe there is a way.

Use the pellet as it was designed to initiate a fusion reaction.

Encase the pellet in a much larger shell, they has very precisely location holes in the shell. Holes that match the location of the incoming lasers so the lasers pass through the shell without affecting it, and causing the normal fusion reaction.

This fusion reaction then ignites the shell and you are ready for a big bang.

In real-life this is sort-of similar to a thermonuclear bomb that is ignited by a fission bomb. Note that this process requires a fission bomb, not something more like a stick of dynamite that the pellet represents. I don't expect any possible future where you ICF reactor could ever generate fusion events remotely close to being large enough to ignite an outer shell for a big bang.

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OP asked in comment - Would all the radiation from a reactor do if you cut off the shielding system, which would have been the superconducting magnets that contain the core plasma?

In a true ICF reactor, there are no superconducting magnets that confine the core plasma - the plasma is "confined by inertia" - the pellet (or futuristic equivalent) simply can't explode fast enough to prevent fusion. The conditions that enable fusion (temperature and density) for ICF are so extreme that the time of containment, though measured in nanoseconds, is still sufficient for high-gain fusion, i.e., far in excess of the conditions at the core of our sun.

You could have magnetic confinement, not to confine the plasma for the purpose of fusion, rather to keep the plasma from damaging the walls of the reaction chamber one the plasma has passed the ICF stage.

I don't expect to see a hybrid reactor that combines ICF and magnetic confinement, I believe this would in practice be a magnetic confinement reactor that uses a novel form of plasma heating - except for magnetic confinement you need the plasma flowing in channels - not exploding from a central point. You would need something more like Star Trek style force fields (beyond known physics) that can contain a plasma that is simply exploding outward.

Though a 2nd question - I thought this was also interesting.

Answer 2

Breaching the reactor will let air in, leading to an immediate end to fusion. Some hot things may catch on fire. The reactor may occasionally make louder noises in normal operation. The reactor operators may wish they were dead in a massive explosion when they hear the whistling of oxygen-rich air entering the reaction chamber, though, since that's going to take a lot of work to clean up and Important People are going to be asking questions and looking for someone to blame.

For an actual explosion:

• Starting from a cold reactor, run an oxygen line from the life support system, and feed in hydrogen or some other flammable gas from...well, find something. Build up as much pressure as the system will take (which won't be much, it's intended to house a near vacuum) and try to start the reactor. This should get you a reasonably loud noise and a heavily damaged reactor.
• Sabotage the fuel storage. A D-T ICF reactor will use pellets filled with frozen deuterium and tritium, which are both essentially as reactive as normal hydrogen, and a boiling point only 20-some Kelvin above absolute zero. Look at Fukushima...a little loose hydrogen can easily blow the roof off. Bonus if the reactor uses tritium: contamination of the vicinity with radioactive material that will greatly interfere with short-term cleanup.
• Engineer a massive failure of the superconducting magnets used to convert the bursts of expanding plasma into useful power. A superconducting magnet can "quench": part of it ceases to be superconducting, and the resistance converts all the energy stored in the magnet into heat. Controlled quenching is used to condition superconductors for use, but uncontrolled (or maliciously controlled) quenching can be quite destructive. The rapid collapse of the magnetic field itself can rip things apart (especially if it's supposed to stay in balance with another electromagnet), and the heat can rapidly boil off coolant in a BLEVE. And the boiling coolant displaces air, leading to an asphyxiation hazard that will require the area to be quickly evacuated.

Answer 3

Short out the capacitors

The one thing fusion reactors have in common, whether tokomak or ICF, is a massive start up power requirement.

A plasma fusion reactor may just need one burst of power, but a ICF needs periodic burst power, each time a pellet enters the chamber. This, for even our test rigs at the moment, means an absolutely giant bank of capacitors, flywheels, and all kinds of ways of storing power. A commercially viable one needs an even bigger bank.

Sabotage this, and, well, have you ever done that experiment in school, where you short out a fully charged capacitor, and the little thing explodes? Ramp that up by millions of times. It may not be a thermonuclear explosion, but it'll be a pretty good sized conventional one, and leave an absolute mess of burning electronics.

A high tech future fusion reactor would be likely to have advances in capacitor and energy storage tech, making the whole thing more energy dense, and therefore more explosive

Answer 4

As much as the movies want to convince you otherwise, explosions are hard. Do you know what the difference is between a charcoal briquette and a quarter stick of dynamite? Time. They both release the same amount of energy. Scale this down to a firecracker, and the only reason it goes bang is because the wrapper holds the gasses in until there is enough pressure to break the wrapper.

There is a huge structural difference between an explosive and a reactor of any kind. With nuclear weapons, for instance, the fissiles are compact into a small space and held there with a conventional explosion until most of the mass has had had the opportunity to convert to energy. In an equivalent power plant, the fissiles are spread out among moderators, coolant, and control equipment. You couldn't get it compact enough to blow up if you tried.

With the hydrogen bomb, things are even worse. They use a conventional bomb to set off a plutonium bomb, and use THAT to set off the hydrogen bomb. It takes an immense amount of temperature and pressure to make the hydrogen fuse, and the biggest challenge is maintaining that pressure for long enough for the hydrogen to fuse.

Over and over again, we go back to the firecracker that needs a wrapper to be an explosive. Power generation equipment always gets in the way.

Let's look at what we think might be a scaled down equivalent: a car exploding. Note that this isn't the engine exploding, it's the fuel tank, and even that only happened with frequency in the movies.

Spontaneous explosion is a quality that is peculiar to chemical energy. That's the basis of all conventional explosives. With all other power sources, it's a challenge to get enough potential into a small enough area.

Answer 5

Lard up your fusion with some fission. And antimatter!

Yup yup yup. Reactors give off energy little by little. When they break they stop giving off energy.

But: how are you powering this fusion reaction? The ones we have on Earth compress regular small atoms until they fuse and then the energy is used to generate electricity which then charges our earth toned electric scooter.

Perhaps though you are using fusion in a spicier way, and inviting its rowdy brother Fission and their weird uncle Antimatter to this party?

https://www.scientificamerican.com/article/antimatter-and-fusion/

The power of fusion

The fuel for such a fusion-driven spaceship would likely consist of many small pellets containing deuterium and tritium—heavy isotopes of hydrogen that harbor one or two neutrons, respectively, in their nuclei. (The common hydrogen atom has no neutrons.)

Inside each pellet, this fuel would be surrounded by another material, perhaps uranium. A beam of antiprotons—the antimatter equivalent of protons, sporting a net electrical charge of minus-1 rather than plus-1—would be directed at the pellets.

When the antiprotons slammed into uranium nuclei, they would annihilate, generating high-energy fission products that ignite fusion reactions in the fuel.

This scenario has boom potential. Nuggets of fissile material all ready to go boom when the antimatter comes. "Don't store the antimatter next to the uranium nugs!" they said. But there was no room for the foosball table and so the nugs got relocated to the antimatter closet. Then when the antimatter got loose the uranium nugs were right there.

Answer 6

Not big at all. Fusion reactors exploding is a popular media phenomenon that does not match the actual science.

Fission reactors are known for their potential to melt down because all it takes to start a fission reaction is assembling a big enough piece of enriched uranium in one place. Once you've done that, the reaction is self starting, self sustaining, and even exponentially amplifies itself for as long as sufficient fissile material continues to be present. Because of that, one of the most major parts of any fission reactor's design is ways to limit, control, and stop the fission reaction.

Fusion bombs are known for producing powerful explosions because they are specifically designed to explode powerfully. They produce the conditions needed for fusion in a destructive manner by detonating lesser explosives in extremely precise calculated arrangements, and the fusion only lasts a brief moment before the necessary conditions dissipate. The result is so powerful because the total lack of any need for the device to remain intact makes it feasible to design it so that the momentary fusion goes far, far beyond the bare minimum conditions for fusion.

Authors of science fiction stories took the dangers of fission reactors, and the relative power of fusion bombs vs fission bombs, and assumed that using fusion instead of fission would amplify the danger of a reactor in a ratio similar to how it amplifies the power of a bomb.

In reality, however, the sustained non-momentary fusion reaction needed for a fusion reactor to produce power requires great effort to actively maintain the conditions under which fusion can occur. The difficulty of making fusion happen at all, not the danger of it, is what makes useful fusion reactors so difficult to create.

A fusion reactor running at peak capacity is already creating and maintaining the strongest fusion reaction that the machinery is capable of. Malfunctions or sabotage would only make the fusion reaction weaker, or stop it completely.

An extremely abrupt rupture of the reactor might result in a small explosion, but the power involved would be no greater than what the reactor ordinarily keeps contained, and it would stop almost instantly. You would get a lot more destruction done by hooking up the power output of the reactor to an actual weapon designed to use that power destructively.

Answer 7

Not the reactor itself.

Many people have mentioned that fusion reactions won't just happen outside of a reactor and it takes a huge amount of engineering effort to make the reaction happen at all, unlike a lump of plutonium which will explode if you squish it fast enough, or hydrogen which occurs as a byproduct form overheating fission reactors.

So instead of damaging the reactor and having it blow up, leave it running. Boost the power output as high as it can go without breaking.

Then (having put nails in all the fuse boxes earlier) short-circuit the output. Blow up the transformers. Melt the wiring. Make some giant sparks.

Or jam the voltage regulator on the high setting so all the lightbulbs and appliances in the whole building go bang.

None of that is going to blow the place apart, though. It's a crazy scientist's lab, right? What else is in here? Got some spare phase gate parts? I'm sure one of those holophasic gluon field thingies has plenty of destructive potential. Okay, that's a bit far-fetched.

But wait, fusion reactors run on hydrogen - an explosive invisible odourless gas. Mix it with air in the right proportions and ignite it, there's your explosion. Storing hydrogen is tricky, so this facility doesn't store it. It stores water, and extracts the hydrogen as needed, using electrolysis. You sabotaged this and left it running for months, so you have all the explosive gas mixture you need. You can't let the whole lab fill with hydrogen over time, though, because any little spark would set it off, though. You'll have to store it somewhere (doesn't matter if it's a little leaky) and then release it not long before you want the explosion.

Answer 8

Reality questions: (I have no idea whether these questions even make sense)

With a tokamak-style reactor, how much damage would be done to the "supporting structure" if the plasma somehow got loose? I'm not thinking of a "boom" here (probably not), but just the damage and rebuilding cost.. I wonder if that's figured into the "fusion-as-ultimate-green-energy" scenarios?

Yeah, it's great if you can sustainably contain the plasma, but what happens if it gets loose? Would it basically just melt whatever the outer shell of the ring is (assuming there's something outside that ring that can manage to deal with that much energy), or would it basically melt down the entire building, meaning you'd have to start over building a.. 2+ billion dollar reactor, and maybe be able to salvage some of the superconducting material from the magnets?

I suppose with an ICF design could you have a large amount of space between the lasers and the target? I'm assuming in a tokamak that would be hard or impossible, unless you could get an incredibly high field strength.

Answer 9

Either as big as you want or no more than Chernobyl scaled for the energy output

Fusion reactors don't exist.^{<citation needed>}

Several of the answers are using the present-tense to explain what they think a fusion reactor will do. That's amazing, since you don't explain anything about the reactor. You don't explain its nature, its size... nothing. Therefore, you really only have two options:

1: How many angels can dance on the head of a pin? As many as wanting.

When it comes to undefined reactors rigged to explode, your best bet is to simply define the damage that you want and move forward.

2: Use Chernobyl as a point of reference.

Yes, Chernobyl was a fission nuclear reactor. It's as close as we can get without an actual fusion reactor. But, let's start with a truth:

Myth # 2: A nuclear reactor can explode like a nuclear bomb.

Truth: It is impossible for a reactor to explode like a nuclear weapon; these weapons contain very special materials in very particular configurations, neither of which are present in a nuclear reactor. (Argonne National Laboratory)

But this doesn't mean a reactor can't explode...

Nuclear reactors can't explode like nuclear bombs. But they can explode, because an out-of-control fission reaction generates a boat-load of heat. Build up enough heat, and everything from water to metal vaporizes, creating pressure. Get enough pressure, and you get a boom.

Yeah... but how much of a boom?

And we're back to having no idea the type or size of your fusion reactor. Don't know how it's designed, what safety features are in play, we don't even know what fuel your reactor will be using, but we can take a guess:

The current best bet for fusion reactors is deuterium-tritium fuel (U.S. Dept. of Energy)

Deuterium is chemically identical to hydrogen (Source). So it's no more dangerous than hydrogen.

Tritium is also chemically identical to hydrogen (Source), although it is a radioactive isotope. The radioactivity could be a believable problem, but the referenced source suggests it would take a lot of it.

Having said that, hydrogen can explode. The Fukushima nuclear power plant experienced a hydrogen explosion. How many people died? None. Five workers were injured. Yes, hydrogen "explodes," but it doesn't explode like TNT or nuclear bombs. Think about the Hindenburg. When it exploded there was a massive fireball — but there wasn't a glass-breaking concussion.

Now, the Hindenburg wasn't contained like a concrete-and-metal encased reactor — but it did have access to abundant oxidant. Whether or not a fusion reactor had access to significant oxidant would be very circumstantial.

Conclusion

I could be wrong, but I don't see a fusion reactor doing anything more than what Chernobyl did. (And, realistically, it might even be safer than Chernobyl due to the lack of all that radioactive fuel — uranium.)

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_{¹ We're not talking about a star here. A large-mass star will burn hydrogen and helium. When it's gone, they'll burn carbon. If they're large enough, they'll burn neon after the carbon. But once a star gets to iron the process of fusing iron absorbs energy. But we don't have that mass. So when a fusion reactor and its fuel mass loses containment the fusing part of the process would die very quickly, leaving the usual nasty mess.}

Answer 10

Sabotage the charging injector. Inject the fuel for 1000+ cycles all at once

At more than a million of degrees there is no material that can sustain that temperature, the magnetic field can contain the plasma, but not the heat. The fusion reactor will work in pulses. No single pulse will be long enough to let a big amount of heat to escape the magnetic field, this is the current design and will be the future design there is no way not even in the future to solve the 1 million degrees problem.

To turn pulses in a continuous supply of electricity there will be more reactors working in parallel, but there will also be a system that will recharge automatically the reactor between one pulse and the other in the fastest possible way. That system will have available the fuel for a big number of pulses. Sabotage that system, inject all the fuel available in one go. In this case what was the reactor power?

A 1 GW reactor designed to be active 20% of the time for 1000 days has the fuel to generate 200GWh. According to this link that power all at once is a little bit more than 180 kilotons.

Edit: by answering to @Christopher James Huff I realised that I forgot to take into account the efficiency. The power in the explosion might be more than double than the electrical output because it would contain all the thermal power. But still it is not very much. The story will have to beef up the numbers.