[ExcelSaga]

It would explode, but for any reactor we’re likely to build in our lifetimes, it wouldn’t be anything like a nuclear bomb. We’ve had nastier explosions in natural gas refineries. There would be radiological contamination from the Tritium and any neutron-activated material, but it would be more of an expensive cleanup than an environmental disaster. It would be dirty though, especially if the reactor had been running for a while, building up dust. What wasn’t radioactive would still likely be stuff you don’t want to breathe or ingest.

TL;DR Boom lots of dead people in the containment structure, expensive cleanup, but nothing like a fission disaster. It would be an uninspiring explosion, but it would be dirty.

[XorNot]

This is wrong in every possible way. There isn't enough mass of hot material in any plausible fusion reactor to even breach the vacuum chamber.

Or for better context: research facilities today regularly lose plasma containment. It's why we don't have practical fusion reactors, but they're already at the plasma densities we would run at (which is an order of magnitude or so better then the Sun achieves).

[mpweiher]

Yeah. There's even a clue in what it's called: a vacuum chamber.

Densities are extremely low, so you only have a few grams of material in the reactor, even at large volumes anticipated for a commercial design.

Furthermore, the reaction is extremely finicky, as demonstrated by what an incredibly hard time we are having creating and more importantly sustaining it. Any deviation from the ideal and it just goes out. So no runaway chain reactions.

https://en.wikipedia.org/wiki/Fusion_power#Accident_potentia...