[quote=@Krayzikk]
Key words are "less advanced" and "possibly more volatile". A fusion reactor in suitably advanced settings could be hand waved as safe due to having certain fictional safety measures, but a less advanced reactor implanted in one's body that may very well not have worked, in a setting that produces most of its technology through Dust, would not have advanced measures like that.

At the bare minimum, a self sustaining reactor breach would produce an immense amount of very, very bad radiation. More likely? An explosion that is, at the size it would be to be implanted in one's body, equal to or just under the size of what we inflicted on Hiroshima.

As in, enough to level a city. And that's without even touching how the tech would be developed given that almost everything in RWBY runs on Dust.
[/quote]

More or less. As it stands, even if you could somehow damage his Fusion Core either by doing enough external damage or somehow getting Gren to literally open himself up for you, the worse that I want him to do is cause a localized radiation leak. You'd have to work a bit harder for him to become a walking warhead. And while Gren is still using the "Old Tech", he has upgraded since he left the White Fang. The fact he won't explode into a Hiroshima bomb is one of the upgrades you could say he got for himself once he cut ties with the White Fang. Removing his new safety features may turn him back into a walking warhead, but right now that's not something he's capable of.