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Comment by w323898 | Hacker News Reader

Fusion was, and for the foreseeable future will be, a boondoggle. In the US it was a cold-war-era arms race program intended to scare the USSR and have them overextend, and now the Chinese are using it for propaganda and scientific Keyensianism.

The fact is, fusion generates neutron radiation that destroys the reaction vessel, making it an unviable technology. Nobody takes it seriously as a source of energy, aside from uninformed people. As cool as the idea of controlled fusion is, it is and will remain science fiction.

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I dunno, my buddy who just got a degree in high energy plasma physics working on fusion reactors might disagree with you.

And really, you just sound like every crank ever who thought X technology was totally unfeasible and always would be -- until it wasn't. So currently attempts haven't found a solution to the reaction vessel destruction problem. That does not mean someone in the future couldn't figure that one out.

OP at least gave a reason: neutron radiation destroys the reaction vessel. No one who's responded has given any evidence for why this is false.

It's not false. But it's also not a universal constant like the speed of light or something, absent a reason why it couldn't be planned for and dealt with, I'm inclined to treat it as an as-yet-unsolved engineering challenge.

Neutron radiation, plus the unfortunate geometric fact that the surface area/volume ratio of a fusion reactor will be low, compared to the fuel rod surface area/volume ratio in a fission reactor.

What this does is ensure that even operating right at the limits of neutron damage to the wall materials, the volumetric power density of a DT fusion reactor will suck. And that will destroy the economics.

Research into vessel liners is ongoing and promising. 7-X is getting carbon-carbon, JET has an upgrade going in about now. It's a materials-engineering challenge, but not a showstopper.

https://en.m.wikipedia.org/wiki/Aneutronic_fusion Nothing is impossible, but some things are highly improbable. I'm all for research, but we should be realistic in our expectations.

In MIT's ARC design, the reactor is designed so you can easily open it up and replace the inner vessel. The vessel is 3D-printed and replaced once a year. Surrounding the inner vessel is a molten salt mixture which breeds more fuel from lithium but is otherwise unaffected by neutron radiation.

This is a regular tokamak design, with a high chance of success since we understand tokamaks very well at this point. Various startups have more speculative designs that deal with the issue in other ways.

A single ARC reactor will use 40% of the world's annual production of beryllium.

The power density of an ARC reactor will be around 0.5 MW/m^3. In comparison, the power density of a PWR reactor vessel is 20 MW/m^3.

Replacing the entire inner vessel once a year would be an operational nightmare. For one thing, it ensures the building the reactor is in will have to be very large, with very large secondary bays where the intensely radioactive material of a spent reactor vessel can be moved and disassembled (generating radioactive fragments and dust).

We don't produce much beryllium because we use need much. It's about a fourth as prevalent in the Earth's crust as boron, for example.

http://periodictable.com/Properties/A/CrustAbundance.al.html

Boron, however, is more easily concentrated (in evaporites). Beryllium is found in pegmatites, which are less common. The estimated resource (not reserve) of Be is 100,000 tons (USGS). This would be enough for ARC reactors supplying just 1% of current world primary energy demand. The estimated world resource of boron is in excess of 1 billion tons.

https://minerals.usgs.gov/minerals/pubs/commodity/beryllium/... https://minerals.usgs.gov/minerals/pubs/commodity/boron/mcs-...

Correction: the deposits are mostly volcanogenic, not pegmatitic. However, they still aren't very common.

Somehow dealing with neutron radiation seems like the lesser problem between it and confining fusing plasma at 100 million K. You make it sound like there's literally nothing to be done about neutron radiation, but something tells me there's probably material scientists interesting in working on that.

It's literally beyond chemistry, the radiation changes the chemical makeup of the materials.

Oh sorry, we didn't realize that you completely understand all of physics and can qualify, without any possibility of error, that any configuration, period, that utilizes fusion will necessarily be impossible because of this physical restriction.

For DT fusion, that's been known for 35 years. It's not just materials, it's power density.

http://www.askmar.com/Robert%20Bussard/The%20Trouble%20With%...

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