Not only are the radioactive byproducts not that dangerous (everything is relative of course). But also they have incredibly short half lives so they go away long before the firefighters turned up.

Technically fission has a similar physical barrier to infinite meltdown. Once the water leaves the core, the reaction stops. It was called China Syndrome, and we wouldn't have worried about it at all, had the physicist that thought it up been a bit more competent with his math skills. Unfortunately, there are plenty of other ways that the reactors that we currently use can catastrophically fail.

I mean, no, it also doesn't have enough hydrogen.