Comment by fpoling
4 days ago
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%!)