Turns out it was an administrative building at the edge of the complex that got ignited by a parachute flare. Russia seized the plant, there was never any remote danger of radiation release. Even if it totally melted down, the danger to the US is pretty close to zero. I think Russia seized nuclear facilities to prevent the Ukrainians from committing false-flag attacks to hype up the world to come and save them. Like everything about this war, nothing is as first reported. Now Ukrainian forces are housing troops and placing artillery batteries in and around school buildings.
Putin is evil, but so is the Ukrainian government and elite who just want to keep the global-level money laundering and grift alive a little longer, and they don't care how many ordinary citizens have to die to accomplish that goal.