Re: Lots of choices- DoS works for physical stuff!
There isn't really anything for terrorists to target with molten silicon, breaching its containment isn't going to harm anyone unless the storage facility is 20 feet from your house.
But this is supposedly grid-scale stuff, so risks becoming something we depend on. Which then means it becomes a potential target. Which then means risk assessments and security costs to prevent someone breaching the containment, adding water and watching the mess. Or just some unexpected failure leading to silicon soldifying and gumming up the works.
(ISTR there's a form of silicon oxide that can explode in a pretty energetic manner as well.)