The energy content in a fusion reactor (even at the 3 GW output scale) is only a few mega joules, or in other words a few sticks of dynamite. Enough to damage t

The energy content in a fusion reactor (even at the 3 GW output scale) is only a few mega joules, or in other words a few sticks of dynamite. Enough to damage the wall. Maybe enough to break the vacuum vessel. At that point the air would stop any further fusion. You might release radioactive tritium, but nothing else that should be felt outside the building. For comparison: The total inventory of tritium would be about 500g, about 50 times the amount of tritium released by fukushima, but the other radioactive isotopes that got released there (caesium, iodine, tellurium) that are much more problematic biologically would be missing.