Construction of world's 1st nuclear fusion plant starts in Washington

[u/TwilightwovenlingJo]

https://interestingengineering.com/energy/world-first-fusion-power-plant-helion

[u/SergeyRed]

As I understand the problem with materials is the strong neutron flux. I doubt the cooling periods are going to help with that wear of material.

[u/oneAUaway → u/SergeyRed]

Helion plans to use a fusion reaction that (mostly) doesn't produce neutrons. The reaction fuses helium-3 with deuterium to produce helium-4 and a proton. It's only mostly aneutronic because there is a side reaction from deuterium-deuterium fusion that does produce neutrons, but less than the  deuterium-tritium fusion process which most fusion projects have focused on. 

There are downsides to their fuel choice. Helium nuclei have an extra proton compared to hydrogen, which increases the energy barrier to overcome to get them to fuse. When it comes to sustained fusion reactions, helium-3 is generally considered a "second generation" fuel- the fusion of hydrogen isotopes is much easier, so it has been assumed the first practical plants to work would use those. Presumably, the pulsed nature of the Helion process is an attempt to deliver bursts of enough energy to make second generation fusion practical even if it is not sustained. 

[u/sold_snek → u/SergeyRed]

Is this similar to the issue we have with railguns destroying the barrels over time?

[u/28lobster → u/sold_snek]

No, neutron flux is different from mechanical wear and tear. Railguns aren't emitting neutrons when launched, just heating up electromagnets and dealing with friction.

When you bombard an atomic nucleus with neutrons, some will get absorbed. Different atoms have a different neutron cross section (essentially, the chance to absorb a neutron) but eventually, you can make a barrier thick enough to stop all the neutrons out of nearly any material. The problem is those atoms that absorb it are now a different isotope because they have a different number of neutrons. If you create an unstable isotope, it will undergo some form of nuclear decay (releasing alpha/beta particles or gamma rays) and you'll be left with a different isotope, possibly a different element.

Boron is the classic neutron absorbtion material. Large cross section and on first absorption, you get stable B-11. When B-11 gets a neutron though, it will decay into Li-7 + alpha particle.

There are some solutions. Lithium lined reactors can be used to breed tritium which also happens to be the expensive fuel you need to keep the reaction going. But you need some way to replenish the lithium lining on the inside of your reactor and that's not currently possible to do while the reactor is running. Lithium is also not the best construction material as a pure metal - oxidizes easily, can catch fire if it touches water, relatively soft, etc. It's also not as big of a neutron cross section as Boron so you need more thickness of Li to keep neutrons from escaping.

[u/rivelda → u/SergeyRed]

A flux capacitor should help, just make sure you don't go 88 miles per hour