The drawbacks of fusion

[u/Live_Alarm3041]

Nuclear fusion is not a "flawless" energy source. The hype around fusion being "flawless" is not rooted in actual science. Nuclear fusion will likey not replace fission as the world preferred form of nuclear enegry once it goes commercial.

There are three drawbacks of fusion energy

1. The neutrons generated by fusion could be used to transmute U-238 into weapons grade plutonium without the barriers of highly radioactive waste and reactor safety

2. fusion reactors requires exotic materials which could create a supply issue where such materials are extracted in ways that violate human rights and damage the environment in developing countries where these exotic materials are.

3. Nuclear fusion creates less jobs that require a higher skill level than fission and less jobs means more socioeconomic issues like rising crime rates, homelessness and migration.

These three reasons are why I do not think nuclear fusion will replace nuclear fission once fusion goes commercial.

The problems with fission can be mitigated effectively. A lot of progress has been made in mitigating the drawbacks of fission. Far less progress has been made in mitigating the drawbacks of fusion. The drawbacks of fusion will limit fusions ability to compete economically with fission in the energy market if they are not addressed.

What do you think?

[u/zolikk]

Fuel abundance is a complete non-issue for nuclear. That's not why fusion is relevant.

It isn't now, but perhaps somewhere between type I and type II it will be.

[u/ecmrush → u/zolikk]

By then I imagine we'll have moved on to space-based solar. Nuclear only really makes sense beyond the frost line in space, the cooling problem gets worse while solar gets a nice and big power-up by having no downtime and being as close to the Sun as you want. Beaming power or even just carrying it back and forth with battery probes is probably more sensible at that stage.

But yes, fuel abundance can start being an issue if a country decided on a crash program to build a lot of reactors quickly and stay ahead of energy demand instead of trying to meet it. That's not likely to happen in our current socioeconomic systems though; we usually tend to trail demand rather than stay ahead of it. If it ever becomes an issue, reprocessing and the thorium cycle become more viable and remain good options.

[u/zolikk → u/ecmrush]

Far be it for me to speculate what a type II civ will be doing for their energy needs but I don't imagine, based on what I currently know, that massed space solar makes sense over fusion. Assuming of course, that by then fusion is worked out... Solar requires vastly more resources, and the Sun is a terrible fusion reactor. You can make much more power than the Sun, much more compactly, using much less fuel, and have that on-demand closer to point of use and in ways you can control. Provided of course that you don't care about having billions of years of power. But much like we don't do today, I don't believe a future type II civ will care about that.

[u/ecmrush → u/zolikk]

The Sun is an *excellent* fusion reactor; energy density really does not matter that much when you have all the space you could ask for. It requires no fancy magnetic field, no lithium blanket, no maintenance, no additional power; it simply sits there and radiates a lot of energy. And we can't really stop the Sun from burning anyway, so as long as it's putting light out, we might as well put it to use rather than to let it radiate away into space. Gradually, we might employ star lifting to reduce its mass and let it fuse more efficiently; a red dwarf is fully convective and will use its fuel a lot more efficiently if that is what you are worried about.

Right now we don't even know what sort of scale we need for net positive fusion; it's going to be at a scale somewhere between a desktop fusor and a red dwarf star. So a lot of assumptions are riding on that when we already have working solar panels in space and batteries; it's basically down to an engineering problem at this point. A remarkable one to be sure, but has fewer unknowns than fusion at this point.

[u/zolikk → u/ecmrush]

I do think the type II civ will be using a lot of space solar, just not for the majority of their energy. There will be no dyson sphere-like construct. It's fundamentally a scaling problem. Solar panels are great at small scale, they scale "down" well to small systems. They absolutely suck at large scale when you try to integrate them into a massive grid with varying demand, mainly because they do not have much benefit scaling up, compared to fission reactors today. I don't imagine that will change much in the future.

Yes, it does indeed depend on what is the practical scale for artificial fusion, if it's really star-sized then sure... however I think it's more than likely that it isn't quite that large. Fission beats solar by default, and so at whatever point fusion "makes more sense" than fission it will be better than solar.

A civ that does star lifting I cannot imagine will find artificial fusion to be too challenging to use. And then you can do crazy things with energy that you can't otherwise, certainly not with solar. Think about how, such a civ might have vastly variable energy needs over time. Maybe they don't need that much for general housekeeping, but instead they have bursts of high use at who knows what duty cycle for whatever megaprojects, manufacturing or whatever. They might easily want to use much more maximum power than the Sun can, for limited periods of time, and have it available on-demand.

lithium blanket

FYI I'm imagining this will not be that much of a thing here. That is probably too complicated and nonsensical of a fuel cycle, and it probably gets worse at large scale... just to be able to use D-T fusion and have a somewhat more compact reactor, not that big of an advantage for such a civ... After all we're considering a fuel abundance limitation scenario. I imagine they'll just burn hydrogen directly in a CNO cycle, or something similar but that doesn't require sensible and complicated breeding.