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realbrownsugar t1_ir8ok7j wrote

Reply to comment by just1monkey in Many scientists see fusion as the future of energy – and they're betting big. by filosoful

Both fission and fusion are both “nuclear” reactions… but that’s where the commonalities end.

In fission, a radioactive isotope (such as uranium or plutonium) is constantly shedding particles and melting down. And the reactor uses graphite rods and heavy water cooling to moderate and manage how much of a chain reaction can take place. Without the rods and water, you could have a runaway chain reaction which could lead to reactor core meltdown… and if there’s more than critical mass of nuclear fuel… an A-bomb explosion to go with the meltdown. (Edit: As u/dewafelbakkers pointed out, this isn't really a concern as reactors don't use anywhere close to the critical mass required for an atomic explosion, nor do they do they enrich the fuel enough to reach such a critical point.)

Not to mention, radioactive decay of spent fuel and remaining uranium/plutonium goes on for aeons.

In Fusion, there is no natural radioactive decay. The natural state doesn’t lead to a meltdown, and there’s not really a need to actively moderate the reactor. In fusion, a lot of energy is needed to get the reaction going as well as to sustain and confine it. If the Torus breaks down for some reason, the magnetic confinement will fail, and plasma pressure will drop and the reaction will stop. And you are left with hydrogen/deuterium gas or heavy water.

It takes a lot of energy to get atoms to collide. Even in an H-bomb, the reaction trigger is provided by an A-bomb. So the energy from the first fission explosion collides the hydrogen atoms together to release the much larger output of the fusion reaction. And, in the fusion reactors, most of the energy spent is trying to get the hydrogen atoms in a hot plasma to collide inside a confined magnetic donut. If the magnets fail, the plasma disappears… sure it might do some damage due to hot gas, but that’s about it.

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dewafelbakkers t1_iraloy9 wrote

>In fission, a radioactive isotope (such as uranium or plutonium) is constantly shedding particles and melting down. And the reactor uses graphite rods and heavy water cooling to moderate and manage how much of a chain reaction can take place. Without the rods and water, you could have a runaway chain reaction which could lead to reactor core meltdown… and if there’s more than critical mass of nuclear fuel… an A-bomb explosion to go with the meltdown.

Formerly in the industry. Most of this is a pretty OK explanation, but that last bit is very wrong and I fear you've been* exposed to some disinformation or are repeating misinformation. You may want to read up on the definition and usage of 'critical mass', but more importantly, there are no fission plants that could accidently result in a nuclear explosion. nuclear accidents can result in meltdown, as you stated correctly, and there are - in extreme and sometime unprecedented circumstances - risks of gas explosions or explosive pressure events... But not nuclear explosions or spontaneous nuclear bombs made from reactor cores. That exists purely in the realm of propaganda and cinema

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realbrownsugar t1_iraoxwd wrote

Ah, thanks for pointing that out! I stand corrected. I was thinking about what happened at Chernobyl with the explosion, and yes… at worst, it could be considered a dirty bomb. There was an explosion, and enough fissile material ejected to be considered radioactive fallout, but it wasn’t an A-bomb. It was a steam explosion from all the coolant overheating.

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dewafelbakkers t1_irb1whx wrote

Yes. Also remember that chernobyl had no proper containment in place, so even a steam explosion and meltdown today wouldn't result in an event like that.

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just1monkey t1_ir8pziy wrote

Thanks! I did like the remote ancillary support structures design of ITER, which means that anyone with bad intentions would need to figure out how to keep the reaction going and keep the tritium flowing in particular. The latter part seems very hard to surmount, but I’d guess that tech improvements that actually let us run fusion with energy gain would also help with “hacks” to both of these for bad actors.

What are your thoughts on this article, written by someone who worked for decades on the Princeton fusion project, which notes in particular the danger of neutron radiation (which seems to erode the very structures intended to keep it contained and protected over time)?

EDIT: Found this!, wherein we are testing out how bad neutron radiation can fuck shit up! Damn!

Also, I admitted at some point that it’s been years since I looked at any of this stuff, and will admit now that I’m about two levels below layman on the topic. Also, I absolutely do not mean to offend anyone or make anyone feel bad (at least not too much if I can help it), but my suspiciousness hackles really get raised when people shut down what seem to be reasonable questions with fanatic fervor. That type of reaction always makes me suspect that there’s some sort of bullshit shield being put up.

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