[Retric]

It’s not that simple.

Fission’s primary form of shielding is generally large pools of water or other coolant which don’t directly become radioactive. Fusion on the other hand needs to maintain a near vacuum so your pressure vessel is under heavy neutron bombardment. However, small amounts of radioactive materials get dissolved in the fission’s water which the goes on to contaminate the primary coolant loop which increased decommissioning costs. Fusion reactors primarily containment vessels becomes extremely radioactive and all the remote handling equipment also needs decontamination, but it’s unclear if the primary coolant loop will need similar types of decontamination.

And by small amounts, divers occasionally go in the same pools storing years of spent fuel rods. https://en.wikipedia.org/wiki/Spent_fuel_pool

Running the numbers the real difference is fission reactors need more protection from the outside world and containment for a potential meltdown. Thus thick though still fairly cheap walls, which generally don’t become radioactive. They last for 50 years and don’t actually cost that much to construct. Fusion however is a vastly more complex device which will also increase construction and decommissioning costs.

[cromwellian]

In ARC the containment is not under vacuum, the reactor chamber is surrounded by molten salt of fluoride and lithium, and so the neutrons produced travel into molten salt where they collide and produce tritium.

It would help to actually watch the presentations. They’ve solved a lot engineering problems from Routine maintenance to blanket Renewal.

[Retric]

ARC reactors due use high temperature plasma in a near vacuum. “The confinement time for a particle in plasma varies with the square of the linear size, and power density varies with the fourth power of the magnetic field,[2] so doubling the magnetic field offers the performance of a machine 4 times larger.”

https://en.wikipedia.org/wiki/ARC_fusion_reactor