The Trouble with Fusion (1983) [pdf]

Which is no surprise. Germany already had dozens amateur (space) rocket clubs way back in 1930, long before people in other countries were even mostly aware of the possibilty of sending rockets way up there.

The US had some catching up to do in the science department, which they accomplished in the end, though rockets loosely based on those initial designs are still in use today.

This is different to today's fusion situation, where we don't know whether there will be any better design at all - because nobody did built something that could be adapted to fit our purpose before us.

Maybe, but maybe not.

Worst features for fusion reactors: 1. they don't exit now and they won't exist for the next 50 years; 2. they produce lots of neutrons, which make the surroundings radioactive

Worst features for fission reactors: 3. they can go Chernobyl, 4. they produce long-living radioactive waste, 5. they are horribly expensive 6. proliferation concerns

How do these things look for a fusion-fission hybrid:

1. fusion reactors don't exist. Well, they do exist but they are well below the breakeven point. For a hybrid, the fusion part has (a very) negative energy balance, but it's more than made up for by the fission part, so being above breakeven is not a concern. The technology to manufacture the fusion part of a hybrid exists today (and has existed for decades)

2. fusion reactors produce lots of neutrons. For a hybrid, this is actually the point of the fusion half

3. fission reactors can go Chernobyl. This is so because the current fission reactors are powered by a chain reaction. This chain reaction threads the very fine line between subcritical and supercritical, in other words a classical fission reactor sits in a very narrow region between a bomb and a fizzle. The fission reactor in a hybrid gets its neutrons from its fusion partner, not via a chain reaction. The beauty of not having a chain reaction is that you can't have a supercritical chain reaction, or a Chernobyl event

4. fission reactors produce long-lived nuclear waste. I agree with you that this is not the big deal that's made up to be by environmental groups, but the fact that you can burn it via a fusion-fission hybrid is a nice bonus point

5. fission reactors are expensive. this is fundamentally a consequence of 3, that they present the danger of going boom. And as long as the fission reactors get their energy from a chain reaction, this danger exists. If you have a design that cannot go supercritical because it does not rely on a chain reaction, this is going to be inherently passively safe.

6. proliferation concerns. Here I simply have no idea how fussion-fission hybrids compare with classical fission reactors. That's why I mentioned the Department of Energy. If they develop and run these new reactors, then proliferation concerns become moot.

Besides all these points, the fusion-fission hybrids have another advantage: they can burn U-238 [1], which makes up 99% of the uranium on Earth. This means not only you have more fuel available, but you don't have to go through the stupendously expensive process of enrichment. Or it can burn Thorium-232, which is 3 times more abundant than uranium. In other words, not only the construction costs would be much lower, but the operation costs too.

Oh, and here's another advantage. Because classical fission reactors are based on a chain reaction that has to be very narrowly confined between supercritical and subcritical, at any given point only a very tiny fraction of the fuel is burning. Nuclear advocates don't like to dwell on that, but they like to point to the flip side of this coin, that the fuel lasts for a very long time (years). However, if you could burn the fuel faster, you can get the same power from a smaller reactor. We could be talking a factor of 100. Since construction costs don't scale linearly with size, a reactor that's 100 times smaller could easily be 1000 or 10000 times cheaper. And we could end up being able to send gigawatt-size reactors to Mars, rather than the kilowatt-size currently envisioned by NASA [2]

[1] https://en.wikipedia.org/wiki/Nuclear_fusion%E2%80%93fission...

[2] https://en.wikipedia.org/wiki/Kilopower

What combustion turbines allow you to do is avoid heat exchangers, and also operate at a temperature much higher than a steam turbine because no solid material needs to be at the temperature of the working fluid. A simple cycle gas turbine (without regeneration) has no heat exchangers. Heat exchangers are expensive; transfer of heat across a solid/fluid interface is not as fast as we'd like it to be.

"Based on our present understanding, D-T tokamak fusion reactors project a cost-of-electricity that is about 50% larger than the projected cost-of-electricity from advanced light-water reactors in the middle of the next century."

We all know what happened to the projected cost of fission reactors -- the projections turned out to be hopelessly optimistic, because of complexity and loss of experience. Fusion would face these problems in even worse form (indeed, ITER's cost ballooned 4x or more past the initial projections.)

The experience with fission has enabled us to calibrate the optimism bias in these projections, with damning results.

Simply being competitive with fission is no longer good enough for fusion to succeed. It has to be significantly better than fission.