[myrmidon]

> fusion power as it gets closer to success and eventual general availability

IMO it is not clear that fusion will ever be useable for power plants: Depending on costs (construction/maintenance/decomissioning), it might never be competitive with (battery backed) photovoltaics (or wind), no matter how much progress we make.

Personally I believe that fusion research is worthwile no matter the outcome, but calling it a "purely academic waste of ressources without positive environmental/economical ROI" might turn out to be correct (playing devils advocate here but this is important to consider, no matter how much pro-nuclear you are).

[simonh]

A lot of the recent Fusion startups seem to be making worryingly unrealistic claims that make me somewhat skeptical.

Whenever they talk about putting a fusion reactor in a shipping container, or on the back of a truck that's a red flag. Any fusion plant capable of useful power output is going to have to kick out enough neutron radiation to need some pretty serious shielding that just makes that impossible.

Another problem is the way they often pitch the energy gain numbers. Q=1 sounds great, the output energy equals the input energy, but that's only the input energy required to maintain the plasma. The actual energy to power the plant and run the heat exchange system and such as a whole (Engineering Gain = 1) is likely to be about 22x that. Then to be economically viable in practice the gain might need to be an order of magnitude or more again.

[tsimionescu]

> Personally I believe that fusion research is worthwile no matter the outcome, but calling it a "purely academic waste of ressources without positive environmental/economical ROI" might turn out to be correct (playing devils advocate here but this is important to consider, no matter how much pro-nuclear you are).

One thing to remember is that a major goal of fusion research is also weapons applications, those that is never publically admitted.

[myrmidon]

Not sure I agree with this; I just don't see the weapon applications of fusion power... Also most participants are either already nuclear powers (US, EU, Russia, China, India) or could just build thermonuclear weapons already if they wanted to (Korea, Japan, etc.)

Or maybe you had completely different weapon applications in mind?

[tsimionescu]

No country in the world that doesn't already have them can "just build nuclear weapons if it wanted", international treaties are extremely prohibitive of that. In particular, if Japan wanted to build a nuclear weapon, it would face tremendous opposition from China, while S Korea would face the same from both China and N Korea.

Also, fission weapons tests are currently banned, which also indirectly bans fusion weapons tests, as fusion weapons require a fission step. ICF experiments perfectly mirror conditions inside a fission-fusion bomb though, so are a way of furthering research into improving the yields or other characteristics of such bombs (which have existed since the early 1950s, this is not some far-fetched concept).

[myrmidon]

> international treaties [...], political opposition

Are just reasons for countries to not want nuclear weapons. But if e.g. Japan announced a nuclear weapon program (or it was uncovered by foreign intelligence) I highly doubt that anyone could/would stop them-- hinder their economy or facilities with sanctions or sabotage, sure, but outright stop them from becoming a nuclear power? Unlikely.

IMO every bigger western-ish nation state has the ressources required to build nuclear weapons; they just lack motivation to do so.

Just consider that smaller states like France were already able to do this in the 1950ies, and relevant helper technologies (computer aided design, simulation, industrial control) are MUCH more accessible and advanced today.

Fusion research, on the other hand, is not going to help with the major challenge in becoming a nuclear power: it does not help with obtaining highly enriched fissile material.

If countries wanted to throw research funds at becoming a nuclear power, it seems infinitely more likely to me that those would go into "innovative reactor research" with the endgoal of producing HEU or plutonium.

[tsimionescu]

I agree with you that there are lower hanging fruit than fusion research for becoming a nuclear power.

I do not agree with you that Japan could in practice successfully acquire nuclear weapons with only economic sanctions to fear. I believe that China would be likely to declare war before allowing Japan to become a nuclear power, and I think it would have significant international support. Of course, that would be many years away, as a last resort if all else failed and their weapons program is nearing fruition. But I do believe it would happen eventually.

[GravitasFailure]

Inertial Confinement Fusion is useful for H-Bomb research, and other styles of fusion are probably tangentially useful for understanding high energy physics.

[jounker]

Electricity for high power directed energy weapons. (This is my guess as to why Lockheed’s skunkworks has been working on compact fusion reactors.)

[danpalmer]

I have never heard of fusion weapons research, or what they would even be. My understanding is limited but where I can see fission leading to weapons, I can't see the same for fusion.

Could you give some more detail? What form would a fusion weapon take? Is it about the laser technology?

[tsimionescu]

The first thermonuclear weapon (or H-bomb) test was successfully completed in 1952. That is, a nuclear bomb that uses a fission reaction to create the conditions for a more pworful fusion reaction, which is either the final step, or is used to power an additional fission step, amplifying the final explosion many times more.

The NIF experiment explained here, which uses a laser to generate X rays by heating the walls of a heavy metal hohlraum, and then uses these X-rays inside the hohlraum to compress a pellet of gas to ignite a fusion reaction is very similar to the conditions inside an H-bomb, which also generates X-rays (via a fission reaction) to compress and ignite a fusion reaction.

The weapons use is relatively simple - fusion reactions expel much more energy than fission reactions, and using the power of a fission reaction to compress and to ignite a fusion reaction inside a large amount of gas expels much more energy than simply exploding the power of the fission reaction outwards.

[bjowen]

The NIF and some other facilities (eg the Sandia Lab Z machine) are for studying fusion plasmas in order to understand their behaviour in thermonuclear weapons first, and possible application in power generation as a distant second. That’s pretty explicit, it’s a way of keeping up nuclear weapons research and maintenance without detonating actual devices and breaching test ban treaties and causing various other messes.

JET, ITER, Wendelstein and other magnetic confinement facilities on the other hand are investigating fusion as a source of grid energy.

[maxerickson]

Thermonuclear bombs are fusion weapons (with a fission trigger).

Having relatively easily handled, high density energy sources would also probably lead to deployment of energy weapons.

[arethuza]

Most modern weapon designs are actually fission-fusion-fission designs with most of the energy actually coming from the final fission step - the latter being driven by neutrons from the fusion step. Things get even more complicated with the fact that primaries are fusion boosted fission and the fusion step contains a fission "sparkplug".

[tsimionescu]

Sure, but the fusion step is still important and somewhat poorly understood, so ICF experiments which mirror the conditions inside the fission-fusion step could be valuable for increasing yields.

[arethuza]

Interestingly, a lot of recent developments in warhead design (e.g. the non-spherical primaries of the W-88) are actually about primary design - so I guess its possible this kind of research also feeds into the fusion boosting component of primaries.