Wasn’t the H-bomb (fusion) supposed to be way more powerful and unpredictable than the A-bomb (fission)? Kinda confused here and I’m certainly mixing bombs with energy production. But if you could give me the essential I’d appreciate it. Thank you.
In: Chemistry
If cold nuclear fusion could be achieved and generate surplus energy it would be safe. Bombs are designed to be unsafe nuclear power stations are designed to be safe.
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To make a fission bomb, you need to get a pile of fissile material together that’s above a certain mass. Then it automatically explodes.
To make a fission reactor, you need to get a pile of fissile material together that’s almost exactly that certain mass. Then you tickle it until it just starts to explode but doesn’t ramp up. This produces heat which you capture as steam.
To make a fusion bomb, you take a fission bomb and use it to compress hydrogen until it fuses into helium. More powerful, yes. Less predictable, no.
To make a fusion reactor, you use huge amounts of power and lasers and electromagnets to compress hydrogen until it fuses into helium. (Alternatively, you get a big enough pile of hydrogen that it compresses itself under gravity, but we usually call that a “star,” not a “reactor.”)
If you screw up running your fission reactor, you have something that will keep producing power (as heat) even after it melts (and melts everything else, including your water pipes, and you get a steam explosion).
If you screw up running your fusion reactor, it turns off, and you have to put a lot of power into turning it back on.
There are more modern fail safe reactor designs for fission reactors.
Answer to first question is overwhelmingly yes.
In very broad terms, fision and fusion are quite opposite of each other.
The actual processes that make fusion happen vs what makes fission happen are quite different. Fission is a process that can be hard to stop once it starts going, while fusion is a process that is hard to keep going and hard tobprevent it from stopping. In fission reactor, a huuuge ammount of material must be present at the core to function, while every viable design for fusion reactor has very tiny ammount of fusionalbe material in reactor. Fusion bomb only works because of very large ammount of fusionalbe material avaliable for reaction and it requires a fission bomb as the trigger.
Fusion is very hard to make work. For bombs, you need a fission bomb to start the fusion bomb off. Fission bombs would be relatively clean (free of radioactive fallout) if it weren’t for the fission trigger. There were early hopes for being able to trigger a fission bomb without a fusion trigger but chemical explosives just aren’t violent enough. If it could be done, the old plans for using nuclear explosions to dig canals and launch spacecraft would be more tenable.
You’re correct both that hydrogen bombs release far more destructive potential than fission bombs, **and** that at least in theory, fusion energy could be a very powerful energy source for power production.
The difficulty there is not in safety, it is in design. To get energy out of nuclear fusion, you have to create conditions of immense temperature and pressure. Essentially we need to re-create here on Earth the conditions in the middle of a star like the sun. At least for now, we do not have any way to create those conditions, make fusion happen, and have power left over at the end of the process to distribute to an electrical grid. So for now, and for the foreseeable future, nuclear fusion power is still at the concept stage.
Having said that, **if** we were able to build a nuclear fusion power station, then you are correct this station would likely be inherently safer than nuclear fission. Nuclear fission requires extensive safety systems to prevent runaway fission leading to a meltdown as well as long-term storage of the radioactive byproducts. A fusion power station would not have to deal with the same risks because it would not be relying on long-lived heavy fuels like uranium and plutonium and, if a fusion reactor were to start failing, the reactions would just stop.
Having said that again, modern nuclear reactor designs are inherently far safer than those at Three Mile Island, at Fukushima, and especially at Chernobyl. No nuclear power system built today — fission or fusion — is as risky as those historical reactors.
A hydrogen bomb is more powerful than a regular atomic bomb, but in those cases we’re talking about an uncontrolled explosion rather than a controlled, steady reaction.
Adding to what others have said, The big difference in safety between fission and fusion is the waste products.
When you split an atom the two halves, called fission products, are often highly radioactive. This presents a problem, in terms of disposing of the waste, and is a significant hazard in the case of a major accident.
The main product of nuclear fusion is helium, which is harmless. There would be some radioactive waste due to a process called neutron activation, but it would not be on the same level as the waste produced by fission.
>Wasn’t the H-bomb (fusion) supposed to be way more powerful and unpredictable than the A-bomb (fission)
Powerful? Yes. Unpredictable? No. I’m not really sure where you got that from. There’s nothing unpredictable about the yield of thermonuclear weapons. Once we fully understood the process of fusion, there was no mystery. Anyway, bombs don’t work like reactors.
To your question, in general, yes, fusion would be much safer than fission for power plants because a power plant using nuclear fusion does not involve any radioactive isotopes and does not produce any long-lasting radioactive waste. Fission power plants needs hundreds of tons of uranium fuel and the fission process turns that into hundreds of tons of nasty and dangerous radioactive waste that can stick around for hundreds of thousands of years.
Fusion on the other hand is just hydrogen and helium. Some of the helium will be tritium, which is a radioactive isotope of hydrogen, but it decays within a few years. Also, the insides of the fusion reactor will become temporarily radioactive from absorbing neutrons, but again, it’s short lived and not super dangerous.
So in short, fusion is much safer than fission because fusion produces basically no dangerous radioactive waste.
Here is the difference between the two:
Fission rips an atom apart.
Fusion smushes them together.
Fission creates radiation.
Fusion does not.
Obviously, this version is super simplified.
Nuclear fission happens whether you want it to or not. What a fission power plant does is it works to control the rate of the fission reaction. But it doesn’t cause it. The fuel in a fission plant wants to be hot, and most of the effort and safety of a fission plant is trying to keep the fuel cool. In fact, the fuel heating the coolant is ultimately how power is generated. When safety systems fail catastrophically and a reaction is said to be in “meltdown” it literally means that the fuel rods have become so hot that they have melted. At this point, stopping a fission reactor is extremely difficult.
In a fusion reaction, the big problem that needs to be overcome is how to start the reaction and keep it going. A fusion reaction, while it can produce an extremely large amount of energy for a small amount of fuel, is very difficult to maintain. More importantly, if you put the fusion fuel on its own into a reactor, nothing will happen on its own. No reaction will happen under ambient condition, unlike a fission reactor. Most research reactors try to get the reaction going compressing and heating the fuel until it becomes a plasma. And then, maintaining the plasma takes a lot of effort as well. If any of these methods for heating or compressing fails, the reaction just stops. No explosion, no meltdown. Just the reaction stopping. This is a great inherent passive safety feature.
Long story short: most of the work in a fission reaction is in slowing down the fission reaction. Most of the work in a fusion reactor will be keeping the reaction going. If safety systems fail, a fission reactor will accelerate, but a fusion reactor will just shut down.
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