This is where I was yesterday. Now I'm more inclined to think the sequence of events went like this:

1. Coolant loss and core exposure.
   
2. Beginnings of meltdown create hydrogen and cesium.
   
3. Hydrogen, cesium, oxygen and nitrogen are vented into the concrete surround building.
   
4. Hydrogen and oxygen go boom, perhaps after the concrete weakens. Cesium and perhaps some a small amount of uranium get dispersed over a wide area.
   
5. But the core survives.

If the core were exposed, it's likely it would steaming, glowing, or on fire.

Now - admittedly it looks like there's no independent monitoring, so unless there's still a TV crew a few miles away, anything could be happening.

The only way to be sure that the core is intact is to check radiation north of the plant.

But I think if there were a massive breach, the evacuees would be much hotter, and there would be thousands of radiation warnings, and not just a handful.