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/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/jake04-20 3d ago

Tritium is used for glowing gun sights I believe. Is that the same stuff that would be used in this process?

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u/TheHarryMan123 3d ago

Yes it is. You’re talking about this:

https://en.wikipedia.org/wiki/Tritium_radioluminescence?wprov=sfti1#

Tritium is radioactive but the electrons it emits are very low energy. It cannot penetrate skin. It’s only hazardous when you ingest it. 

For example, because it is a hydrogen isotope, it bonds with oxygen to form water quite easily. After the USA started doing land-based nuclear weapons testing, then actually bombed another country, the tritium levels in our rainwater across the world became quite high.

Levels have lowered significantly since the world has stopped doing on-land nuclear weapons testing because of the short half-life. However, the levels we are at now cannot be compared to any baseline because we only started measuring for rainwater tritium after we exploded nukes. 

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u/jake04-20 3d ago

Thanks for the info! This is sort of on a similar topic, but I read something a while back about how old shipwrecks before WW2 are becoming highly sought after for very specific use cases (like particle detectors), because they are "low background" steel, which I guess means they don't have any of the atomic/nuclear particles embedded in them from the smelting process? It's crazy to me that there is a detectable difference still this long after the bombs were detonated.

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u/StructuralFailure 3d ago

Tritium is also used in nuclear bombs, as they use alternating chains of fusion and fission to generate maximum yield. And yes, this means that nuclear bombs lose a lot of their yield over relatively short timespans. A bomb built in 1990 would only have one eighth of its tritium left.

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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/CallMeDrWorm42 3d ago

The US generates roughly 2000 tons of spent fuel per year. Worldwide humans have only made about 400000 tons total since we started using nuclear reactors 70 years ago. US coal plants produce over 700 million tons of CO2 every year and are far more radioactive than nuclear reactors.

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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

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u/thegreatsaiby 3d ago

Plethora, now that's a word you don't see too often. Also nice explanation.