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same shit every day, on god (infosec.pub)

submitted 2 weeks ago by fossilesque@mander.xyz to c/science_memes@mander.xyz

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[–] brucethemoose@lemmy.world 1 points 2 weeks ago (3 children)

I just realized…

I don’t like fusion.

They say it’s clean, but 14.1 MeV neutrons are no joke.

https://en.wikipedia.org/wiki/Neutron_temperature#Fast

14.1 MeV neutrons have about 10 times as much energy as fission neutrons, and they are very effective at fissioning even non-fissile heavy nuclei. These high-energy fissions also produce more neutrons on average than fissions by lower-energy neutrons. D–T fusion neutron sources, such as proposed tokamak power reactors, are therefore useful for transmutation of transuranic waste. 14.1 MeV neutrons can also produce neutrons by knocking them loose from nuclei.

On the other hand, these very high-energy neutrons are less likely to simply be captured without causing fission or spallation. For these reasons, nuclear weapon design extensively uses D–T fusion 14.1 MeV neutrons to cause more fission. Fusion neutrons are able to cause fission in ordinarily non-fissile materials, such as depleted uranium (uranium-238), and these materials have been used in the jackets of thermonuclear weapons. Fusion neutrons also can cause fission in substances that are unsuitable or difficult to make into primary fission bombs, such as reactor grade plutonium. This physical fact thus causes ordinary non-weapons grade materials to become of concern in certain nuclear proliferation discussions and treaties.

How are reaction chambers supposed to deal with that? It’s not very sustainable if the whole assembly breaks down and turns radioactive over time.

[–] JATtho@lemmy.world 4 points 2 weeks ago* (last edited 2 weeks ago) (1 children)

The scientists didn't joke about that tokamaks will be a great neutron factory/highest neutron flux available. Yes, neutron activation of the reactor walls/components is a problem that we need to solve. However, transmutation of lithium to tritium is required for the reactor to work in the long term, so having a high neutron flux source is a plus in this regard. (and a negative in all aspects of structural integrity...)

The volume amount of activated material that would come out from tokamaks is a fraction compared to the literal tens of tons half-burnt uranium that takes way too long to decay to safe level. The more angrier the radioactivity, the less time it takes to decay away.

[–] brucethemoose@lemmy.world 1 points 2 weeks ago* (last edited 2 weeks ago) (1 children)

literal tens of tons half-burnt uranium that takes way too long to decay to safe level.

I mean, breeder reactors? Also it's still not that much, especially compared to the economics of everything else.

Anyway, what I didn't realize was these are 14 MeV neutrons, unless they crack D-D fusion. That's... very different. That's more destructive, and harder to deal with, than fission neutrons.

...To expand on this, I'm somewhat skeptical of all nuclear now. It's fine, it works great, fusion is a noble pursuit. But it just takes too long to set up to stave off carbon emissions.

[–] JATtho@lemmy.world 1 points 2 weeks ago

Fresh PWR fuel is ~4% U-235 and the rest is non-fissile uranium/cladding. ~95% of the potential energy still locked in the "waste" after spending ~2 years in the reactor. Breeder reactors would mean converting greater fraction of this mass into usable energy.

Running PWR core has be at +150 Bar to have +300*C outlet temp - so if something goes wrong it goes wrong like Fukushima. The fuel can stay in the core only until economics say running the plant at less than 100% design power isn't profitable. Every 18/24 months the plant is needs to shutdown for maintance few a weeks to months. I don't like PWRs.

"regular, i.e. non-breeder" MSRs that would just use uranium would be a massive improvement - both in safety and efficiency. Heat a massive silo of (secondary coolant) salt to +500*C with MSR, do the reactor repairs while this reserve runs the turbines, resume MSR. The issue is - politics, fear, and too little research in handling molten salts.

[–] very_well_lost@lemmy.world 3 points 2 weeks ago

Fusion neutrons are able to cause fission in ordinarily non-fissile materials, such as depleted uranium (uranium-238), and these materials have been used in the jackets of thermonuclear weapons.

Fun(?) fact: something like 50% of the energy output of thermonuclear bombs comes from secondary fission events in the bomb casing triggered by the high energy neutron flux of the fusion reaction.

[–] REDACTED 1 points 2 weeks ago

I'm sure there is a good reason why fission has always been "5-10 years till it's ready"