Afaik what makes fusion hard is maintaining the conditions that allow fusion to occur. Because of this, it’s quite safe - if anything goes wrong, it’ll just stop working.
Yes they do exist, link elsewhere in this thread, Helion have a 7th generation nuclear fusion reactor fusing once every ten seconds or so. https://www.youtube.com/watch?v=_bDXXWQxK38
(It's not surplus of power, but it is repeatable fusion actually happening).
I expect that the containment vessels will get very radioactive.
But all a bit hypothetical, since none exist