Comment by steve_avery | Hacker News Reader

Comment by steve_avery | Hacker News Reader

I have personally taken a tour of the NIF at Livermore. The guide was an old hand, who constantly remarked about the efforts of NIF towards "stockpile stewardship," ie the maintenance of the US arsenal of nuclear weapons. It seemed like NIF was all about the stockpile stewardship first, and fusion research was a secondary consideration.

The capability of the NIF to get positive energy from the energy that they impart on the Hohlraum itself is neat, but I constantly discount any milestones that Livermore/NIF report, because the inertial confinement approach has such higher barriers to commercialization than tokamak style approaches, that I just consign it to "boondoggle" in my head.

Yeah, the lasers could be 20x more efficient, and yeah, they probably could figure out how to pump 10s of targets into the chamber per second, but the energy extraction is just completely missing from the considerations. The engineering challenges are a whole 'nother level for NIF, a big barrier to usability.

Seems like energy extraction would be similar to other D-T designs: surround the reaction chamber with molten FLiBe or lead-lithium and run some coolant pipes through it.

> surround the reaction chamber with molten FLiBe or lead-lithium

So manufacturing fusion reactors would use a lot of lithium, which is already in short supply. That would be an interesting complication with the demand of lithium for electric vehicle batteries. Maybe the Li supply situation will be eased by then.

The quantity of lithium required is miniscule, but would require a fair bit of enrichment to eliminate the Li-6. The limiting resource is the inner wall for which no known material other than double the annual world production beryllium is even close to sufficient

What is your opinion of ITER? https://edition.cnn.com/interactive/2022/05/world/iter-nucle...

Personally my money is on SPARC as a demo plant and its planned successor ARC as a commercial power plant prototype. Unlike ITER these systems use high field strength superconducting magnets, which directly translates to a much smaller machine for the same energy gain. Because of the smaller machine size, it can be built much faster than ITER. The company building SPARC plans to achieve first fusion around the same time as ITER, and since their machines are smaller, they should be able to move faster. That said ITER will be fantastically useful for proving a lot of science, and I am happy we have so many viable fusion projects in the works.

https://cfs.energy/news-and-media/new-scientific-papers-pred...

ARC's volumetric power density is just 40x worse than a PWR's reactor vessel, vs. 400x worse for ITER. Neither appears to be on a route to an economical power plant.

I’m not sure I follow, but you’re saying the power plants are very large relative to their power output, and this size correlates to cost, thus making them so expensive that they are not economical?

You’re probably right, but I guess what I’m saying is that we’ve never had a fusion power plant that produces net energy gain at any cost. I believe SPARC is on the path to doing so. It will still take a long time to make fusion actually affordable. For what it’s worth I am a huge advocate of wind and solar power. But fusion is neat and I’m excited for us to get to a point where we actually have sustained Q total greater than 1.

Yes, that's right. View it this way: a fission power plant and a DT fusion power plant are pretty much the same, except for the reactor. The fusion reactor is many times the size (and mass) of the fission reactor, made of much more sophisticated materials, with a much more complex design, operating at higher stresses (loads on supports of the magnets, thermal power/area at the wall, neutron flux). So how is it that it's expected the fusion reactor will produce power more cheaply than the fission reactor? Note that fuel is today a small fraction of the cost of power from a fission reactor.

Ah, yeah that is totally valid. My thinking is not exactly that fusion power will be cheaper than fission any time soon, but that the technology has the potential to deliver safer power, and as important as wind and solar are to our transition over the next few decades, I believe that fusion has the potential to deliver much higher levels of power than wind and solar, allowing for new uses for electricity previously considered impractical. I wonder what kind of new manufacturing processes we can come up with if we have enough power to deliver huge amounts of process heat, for example.

I agree with you that in a practical sense fusion power will not be economical in the next 50 years, but then solar power was not economical for most of my life either. I am excited for the technology to get to the point where at the very least it is producing power, as this will stimulate more investment in lowering the costs, and has been such a dream for longer than I have been alive.

Solar and wind potential is enormous. The current world average primary energy demand is 18 TW, but the Earth is constantly being struck by 100,000 TW of sunlight. In no sense is a shortage of sun and wind an argument for fusion.

As for safety, the problem with fission isn't safety, it's cost. Trading off economics to obtain better safety is solving the wrong problem.

If fusion is not to be economical for 50 years, it will be competing against renewables (and storage) that have gone fully down their experience curves. In a world fully powered by PV, on the demonstrated historical experience curve, the LCOE from PV could be below $0.01/kWh (in today's dollars). Fusion will have a very difficult time competing against that.

Tokamaks are science projects and confusing them with electricity generators benefits no-one.

I'm a complete layman when it comes to ICF, but I'm assuming that there is a scaling factor between surface area and volume that would eventually help here? As in, the lasers initiate fusion on the surface of the fuel pellet, which propagates the fusion into the interior of the pellet in a chain reaction / positive feedback kind of way. So that if you increased the surface area of the pellet by a factor of 10, you'd get 100 times more total output energy (since there is 100 times more mass in a pellet with 10 times the surface area). So you'd need 10 times the current input power, but would get 100 times the output power.

That won’t work, I don’t think. You can’t make the pellets much larger because laser nonuniformities and hydrodynamic instabilities will kill the implosion; there will be no fusion at all. But that’s not a problem, you see, because in a commercial reactor you’ll have a pellet factory making the required one million targets per day, and they will be injected into the chamber 10 times per second, with practically no down time. And each shot will have gain > 100 to get net energy out.

That’s pretty much what this design would require for continuous operation.

But I cannot tell if this comment is being facetious or rather optimistic. Therefore, I’ll agree!

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