So yes, every nuclear reactor that thinks and sooner later gets breached: is a ecologic disaster. And YOU certainly would not like to live close to it or be depending on fish fished there.
I'm curious as to how a fusion reactor can be an ecological disaster.
Yeah, the fuel will spread all over the ocean, but the fuel is hydrogen, so it's not like we're going to notice a few kg extra hydrogen in an ocean that is 1/9th hydrogen.
The fusion byproducts are tritium (again, hydrogen), and helium (chemically inert, and part of the atmosphere).
The shell? It might get irradiated. But slightly radioactive iron isn't really a meaningful disaster, unless you've managed to stick a megaton or so of iron into the 500 cubic feet of that reactor (hmm, 7 foot by 10 foot. Wonder if that's seven feet in diameter and ten tall, or seven feet tall and ten in diameter?). Hint: a million tons of iron won't fit into that volume....