No. But concrete can crack during, say, an earthquake.
And I assume concrete can also lose integrity (melt? vaporize?) under very high temperatures.
The summary is that yes, typically concrete would melt at temperatures anywhere in the range that you'd expected a molten core to be at.
My understanding is that newer designs have a "core catcher" under the reactor made of something more resistant than concrete, but this unit doesn't.
No. But concrete can crack during, say, an earthquake.
And I assume concrete can also lose integrity (melt? vaporize?) under very high temperatures.