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Comment by vjaswal | Hacker News Reader

I added a link above to a good talk from Dennis Whyte. I think it will help address your question about the additional engineering issues in a commercial reactor based on ARC.

In short, from my basic understanding, there are quite a few additional major challenges involved with fusion power generation. e.g. After creating net-positive fusion, the heat must be efficiently extracted without stopping the reaction. Also tritium must be continually extracted from the FLiBe (fluorine-lithium-beryllium) bath that stops and collects neutrons and extracts the heat.

Since I'm a total novice in all this, I don't know if these require incremental innovations or major advances. But from the video, the problems mentioned seem to be more tractable than achieving fusion ignition or Q>10.

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One major issue is that providing enough fusion power with ARC reactors to power the world economy would require 100x more beryllium than the current estimated global resource (not reserve). Only a bit over 200 tonnes of Be is mined every year right now. It's not a common element.

Abdou's team (the fusion engineering guy at UCLA) rejected molten salt blankets for this reason, among others, after trying really hard to get them to work in studies.

One big problem with fusion is the low power density. I harp on that a lot, but it's been known to be a very serious problem for decades. ARC's power density is 40x worse than a PWR's reactor vessel. It's difficult to see how fusion can beat fission given this. I suspect the optimistic numbers for fusion come from using a way too cheery cost estimation methodology, something that would predict fission is far cheaper than it actually turned out to be.

Interesting, thanks for the info.

I was always somewhat concerned about the abundance of critical raw materials for ARC or other fusion projects. I had assumed that the rare-earth elements in the REBCO tape, e.g. yttrium, would be constrained. I didn't suspect that beryllium could be a limiting resource. But I wonder if the lack of supply is related to true scarcity or just to a lack of a profitable market currently.

These are all questions I'd want to ask domain experts in mining and fusion.

But I agree that fission would be a better solution for baseload, at least for the next 10-20 years. If only newer modular designs were actually approved...

The ARC design (see https://arxiv.org/abs/1409.3540 for details) uses surprisingly little yttrium. The superconductor is only about 1% of the tapes, and the tapes are only a faction of the coils, and the coils mass is just a fraction of the mass of the coil support structure. I think the total amount of yttrium will be in the tens of kilograms, if that.

I have a suspicion that this is being funded at all because the magnet technology would be useful in non-fusion contexts (hybrid electric aircraft, superconducting generators in wind turbines.)

In contrast, IIRC a single ARC reactor of that design would have 90 tonnes of beryllium (although that could be reduced by half if the secondary loop used a different molten salt.)

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