I mostly didn't follow the talk about confinement, but I am slightly concerned about neutron activation. He3 fusion is more "neutron-light" than it is completely aneutronic. Operating at reasonable power levels, the reactor is going to be fairly radioactive after a few years. Widespread adoption of fusion is going to require the general public to be more relaxed about low level radioactive waste than they historically have been.
The quotes about total system efficiency is also odd. "95% efficient"? They're not planning on capturing heat energy, so neutron heating is totally wasted, and they're talking about using entirely resistive 12 tesla magnets, which will also throw off a lot of heat.
A fusion reactor vacuum vessel will be bigger than the core of a fission reactor of equivalent power, certainly. But I wonder if a better metric is containment vessel size: there's a lot of very radioactive, very contaminated equipment inside a PWR containment vessel that isn't the core itself.
>orders of magnitude more
Really? Wikipedia says "a typical large 1000 MWe nuclear reactor produces 25–30 tons of spent fuel per year". I don't see a commercial fusion reactor being quite that bad, unless reactor lifetime ends up being very short.
Helion's promotional images keep showing the reactor vessel in a shipping container, which is narrowly true, but doesn't show the support equipment on the other side of a five meter thick concrete radiation shield. No vacuum pump near a running fusion reactor will survive long.
There are all sorts of fascinating engineering problems for a commercial reactor. Photos of the Wendelstein 7-X show it covered with ports for sensors, which you couldn't do with a power reactor, because anything you attach directly to the vacuum vessel will be destroyed. It'll probably end up terribly ugly, the usual intestinal tangle of any industrial plant, a big spiky sausage with pressure sensors at the ends of long tubes to reduce their neutron flux. If you have to mount any sensor directly to the vessel then you use ten or twenty fold redundancy, since replacement is impossible.
After five years of operation, if you go to replace a sensor on the vessel and the threaded fitting crumbles away when you apply the wrench, what do you do? Weld on another one? What's the weld heat-affected zone look like inside the steel after it's spent five years soaked in hot hydrogen, helium, and is richly marbled with transmutation products, dozens of odd elements you don't ordinarily choose to alloy steel with?
Those particle energies come from D-T fusion. Helion is doing a hybrid of D-D fusion, which produces lower-energy neutrons comparable to fission, and D-He3 fusion which does not produce neutrons. They say the combined reaction will produce only 6% of its energy as neutron radiation, compared to 80% for D-T. There will be some D-T side reactions, but not much.
Reactor size depends on the design. For tokamaks, output scales well with reactor volume. But it also scales with the fourth power of magnetic field strength. Two well-funded startups are building tokamaks with newer superconductors that support stronger magnetic fields, allowing them to get the same output as ITER from much smaller reactors.
Other designs have different scaling laws so aren't necessarily any particular size. Helion for example is pretty compact.
The quotes about total system efficiency is also odd. "95% efficient"? They're not planning on capturing heat energy, so neutron heating is totally wasted, and they're talking about using entirely resistive 12 tesla magnets, which will also throw off a lot of heat.