One of the kids has decided she doesn't like her life situation and apparently thinks blowing up the power plant is an appropriate way to express this. At least Ellie assumes this is the reason for the array on the floor of the least-used storage closet, and she thinks her reasoning is pretty sound, given Patty's general attitude and the books Ellie's seen her poring over.
Terrifying as it is, this is one of the kinds that can only be safely disassembled from the center, so she gingerly steps in, clutching at one of the sets of shelves that the array runs under to assure her balance.
Something feels horribly wrong once she reaches the middle, even more than she expected, and before she can remove any of the central corundums or even just step back out of the circle she falls unconscious.