Comment by myrmidon
4 days ago
What is your exact scenario for cheap fusion?
Because IMO the only approach that is even capable of delivering here is the Helion one (=> direct conversion). And that design is incredibly far from ready, the whole approach is completely unproven and their roadmap is mainly wishful self-delusion (from what we can tell by evaluating past milestones, like "first 50MW reactor finished by 2021"-- there is no 50MW reactor even now).
From my PoV, ITER-style tokamaks are the most conservative/certain design, and also the furthest along by far. That would imply:
=> Cryogenics for the magnets
=> big hightemperature vacuumchamber for plasma
=> all the thermal/turbogenerator infrastructure needed in conventional plants
=> super high neutron radiation flux (this is a problem)
I just don't see where you save anything. This is basically just a fission reactor, only a magnitude more complicated and demanding. I absolutely don't see how it could ever get significantly cheaper than conventional nuclear powerplants.
Fission reactor has to be big and has to deal with storage of a lot of nuclear waste and must implement a lot of expensive measures to stop runaway reaction in case of unexpected events.
Fusion has none of this. Assuming Q >> 1 will be demonstrated in a design that can be commercialized the next biggest problem is dealing with high-energy neurons on a scale never experienced before with potential much faster degradation of materials than anticipated leading to prohibiting operational costs.
That's a problem, but it's not necessarily even the biggest problem. Other huge problems include the shear size of the machines per MW of output (and hence cost per MW), coupled with their dreadful complexity and the difficulty of keeping them operating when they become too radioactive for hands-on maintenance. Designs typically just assume the reactors will be reliable enough, when there's no empirical evidence to support that (and the one study that tried to estimate uptime based on analogies with other technologies found the reactor would have an uptime percentage of just 4%!)
Helion's promised dates were conditioned on funding, which they didn't actually get for several years. Adjusting for when they did get funding, they're pretty much on track.