wwarnout t1_ir6xes8 wrote
As much as I would love to see fusion become a reality, there are two problems that few engineers talk about:
First, when they talk about progress regarding getting to a break-even point (as much energy produced as the amount used to produce it), they usually only talk about the energy that goes into the laser (or other device used to initiate the fusion reaction). However, this is misleading, because it ignores all the other input energy required for the complete operation. So, when they claim the fusion energy produces was 70% of the input energy (which sounds very promising), the total input energy was actually much higher. In reality, they are getting out just a few percent of what they are putting in. See https://backreaction.blogspot.com/2021/10/how-close-is-nuclear-fusion-power.html
Second, tritium is needed for the fusion reaction, but the global supply of tritium is only about 25 kg. While it's true that some fusion reactions can produce more tritium, the supply is so low that they could have significant problems getting to the point where a continuous reaction can be sustained. See https://www.science.org/content/article/fusion-power-may-run-fuel-even-gets-started#:~:text=Fusion%20reactors%20generally%20need%20a,%2C%20or%20tokamak%2C%20gets%20burned.
JackSkiSensei t1_ir79iwf wrote
Are there challenges, absolutely. But does that mean we just give up?
JET’s latest result for a prolonged pulse gives huge confidence for ITER, and I’m fully onboard that fusion on the grid won’t be any time soon. Fusion won’t solve our generation it’s to solve the next.
First: Everyone talks about the Q number being power into reactor vs power out because no one knows what the rest of a future plant will need power wise. A bit like a car engine having its BHP tested at the flywheel, it’s tells you the power of the engine. Drop that engine in a mini, mustang or 18 wheeler and test power at the wheels; the numbers are going to be drastically different.
Second: The civilian supply of tritium is short (your number above). But it has dual use so I bet there’s a lot more knocking about. Plus there’s a lot of interesting work going on with lithium and tritium breeding.
CriticalUnit t1_ir9b09h wrote
> Are there challenges, absolutely. But does that mean we just give up?
No, it just means we need to be realistic about the challenges and how far in the 'future' the reality of fusion energy actually is.
Utterlybored t1_ir9u0ke wrote
And the benefits are so potentially enormous, we can’t afford NOT to pursue it with great vigor.
celaconacr t1_ir76y3x wrote
Yes I think it's still a 50 years away technology. SPARC looks promising with its magnet technology and small size (so I assume less tritium).
The target Q factor is 2 but it could be as high as 10 which is atleast approaching a real net gain. We probably need a much larger q factor to make it a viable power source though. Wind, solar and other renewables have become really cheap.
Hiphoppapotamus t1_ir7r5x1 wrote
Fusion faces massive challenges, but neither of these are showstoppers.
Laser-induced fusion isn't a realistic prospect for power generation at the moment because those big lasers aren't very efficient. It's still worth doing because there's a lot of interesting physics we can explore in those labs. Magnetic fusion doesn't suffer from wall-plug efficiency issues so much, and is a more realistic option for an economically viable reactor.
Scientists are probably quite blasé about efficiency calculations because, once you reach ignition, increasing Q to the value you need isn't so difficult (certainly easier than getting to Q=1 in the first place).
Regarding tritium availability, every tokamak power plant design features a tritium-breeding blanket made of lithium. This is not trivial, but it's by no means the biggest technical challenge faced by magnetic fusion devices. These tend to be related to plasma stability issues and surface heat loads on the inner walls of the reactor.
Sir_Osis_of_Liver t1_ir9zeye wrote
Your first point is almost universally glossed over in reporting, especially in the big media outlets.
I always get a chuckle out of these articles. We've been building fission reactors for almost 70 years and can't build them economically, and they just use hot sticks to heat water.
Now they're working on suspending a plasma stream using super conductors and magnets, then somehow extract the energy to heat water. Even if they get to the point of having a stable, sustainable reaction, the economics are going to be terrible.
dewafelbakkers t1_irao5r7 wrote
This is the point that always gets me. So many people in the solar and wind for some reason also support fusion. But when it comes to conversations about fission, it's too time consuming to build, it's too expensive, the supply chain isn't there, it's too complicated, etc.
But then in the next breath it's all about how.excited they are for fusion.
Its like, friend, how fast and cheap do you think think massive centralized fusion plants are going to be when they are commercially viable (in 2075. Or 2100)
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