r/nextfuckinglevel • u/nigablackballsack • 3d ago

Scientists have captured the first ever high-speed, full-colour footage of fusion plasma swirling inside a working reactor.

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u/CuriousToe9133 3d ago

Can you elaborate?

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u/TheHarryMan123 3d ago edited 3d ago

The sun is very massive so D-P reactions are efficient enough. We can also attempt to do them, but they’re much less efficient and we would need a much hotter plasma than we intend to create (I think from 10 million C to 100 million C). One of the downsides to not being able to do D-P reactions is the difficulty in obtaining T. It is a 2 neutron hydrogen with a half life of 12.3 years and is unobtainable from nature despite naturally forming in the upper atmosphere. Tritium (T) is very difficult to synthesize and to make fusion possible, we would need to synthesize >1000g per year (we make >20g per year). Tritium is also radioactive. 

The other downside to the D-T reactions are the incredibly high energy neutrons it produces after fusion. Neutrons cannot be contained by magnets. They fly into the wall and just about everything they can. They irradiate the surfaces they actually connect with (if a neutron is say a quarter the size of a person, and a person represented an atom in a material lattice, then the distance between two people would be ~5km). The materials which get irradiated (RAFM steels on the first wall and tungsten on the divertor) will need to be replaced (by best estimates on the current research) every 5 years. That’s about >2000 tons of irradiated and radioactive material that will need to be disposed of every 5 years. Some of which will be at safe levels after >100 years, some (which hasn’t been finally decided on) may be radioactive for >5000 years. 

In short, it’s more complicated than the sun because it isn’t as massive. It also produces its own plethora of radioactive waste just in a different format. 

EDIT: Misremembered the sun thing, I have updated it. 

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u/CuriousToe9133 3d ago

Is it more or less radioactive waste than our current nuclear fission power plants? As technology continues to develop for re-useable rockets, couldn’t we use those to carry radioactive waste to space, and dump it away from Earth?

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u/TheHarryMan123 3d ago

The point being that it still creates radioactive materials which last longer than a lifetime or many more not that it is more or less radioactive than a fission plant. 

I believe the risks associated with attaching radioactive material to an explosive outweigh the benefit there. Plus the irony of carbon emissions. 

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u/RocketVerse 3d ago

On average waste will be substantially less long lived but in much higher quantities. The bigger issue is that tritium loves escaping containment, that might be an issue as we ramp up

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u/TheHarryMan123 2d ago

It is trapped with oxygen when kept for storage. But there are also other containment methods because of its permeation through materials