3 ms·
I think there is a zeroth problem here, which is how to get the heat from the plasma to the water. You have a fusion reactor making hot plasma that also needs t
by TaylorAlexander 4y ago
I think there is a zeroth problem here, which is how to get the heat from the plasma to the water. You have a fusion reactor making hot plasma that also needs to have water circulating in the right way. From what I gleaned from some fusion presentations the solution to this is itself an engineering challenge.
- pfdietz 4y agoIndeed. As I mentioned upthread, the limits on power/area at the first wall of the reactor lead to DT fusion reactors having horrible volumetric power density. Their "figure of demerit" vs. fission is roughly (radius of plasma)/(radius of a fuel rod).
- Symmetry 4y agoFusion plants also need to absorb the neutrons coming out of the reactor and secure themselves a supply of tritium for their reaction. The most common solution is to do all three with a blanket of molten lithium that can absorb neutrons and heat from the reaction, transmute into tritium, and go through a heat exchanger with water to heat it up.
- willis936 4y agoLithium fission also releases a nice bit of energy.
- robocat 4y agoLithium fission would be into Hydrogen and Helium - definitely not releasing energy. Do you mean that Lithium fusion with a proton or neutron releases energy?
- willis936 4y agoNo I do mean fission. Li-6 fission releases 4.8 MeV. Li-7 fission consumes 2.466 MeV. https://en.wikipedia.org/wiki/Tritium#Production https://en.wikipedia.org/wiki/Tritium#Production There's a lot of lithium being mined for batteries. Just centrifuge out Li-6 or isolate it with some other clever means. Not much is needed for fusion fuel compared to industrial scale consumers of lithium and it's a healthy boost to heat output.
- ncmncm 4y agoMolten lithium would interfere with your magnetic containment. You need a diamagnetic like LiH. Extracting tritium from a thousand tons of radioactivated lithium hydroxide at PPB concentration is left as an exercise for the ambitious reader. Good luck.
- ncmncm 4y ago(Lithium hydride, not hydroxide.) Other neutron absorbers are contemplated, but extracting tritium from them on PPB concentration is no easier.
- compumike 4y ago"Fusion Reactor First Wall Cooling" https://www.youtube.com/watch?v=bHJyoqDO0zw https://www.youtube.com/watch?v=bHJyoqDO0zw talks about the steady-state heat transfer out of a proposed tokamak design. Around 1:09:23 they show "1.5 GW" deposited as "0.3 GW from radiative photons -> surface heating" plus "1.2 GW from 14.1 MeV neutrons -> volumetric heating". Designing the first wall and the volumetric blanket are, indeed, engineering challenges.
- HPsquared 4y ago1.2 GW worth of neutrons is rather a lot. Neutrons cause damage to materials (e.g. disrupting the microstructure) and also make elements radioactive through neutron capture (activation products). It's a pretty complicated issue really.
- ncmncm 4y agoUsually we spell that "intractable".
- DoreenMichele 4y agoSometimes people know enough to see things as merely complicated. They usually can't adequately explain why in a single forum comment.
- ncmncm 4y agoGenerally somebody should have explained somewhere. But it is not considered very interesting, because nobody seiously expects to ever need to solve it.
- DoreenMichele 4y agoSometimes, it is explained somewhere and it doesn't matter, no one is listening. This topic is not one I'm personally familiar with, so possibly making an ass of myself, but (shrug).