What would happen if a Tokamak fusion reactor exploded?

I can't seem to find any detailed information online on this particular topic, for some reason. Now, off hand, I would think the consequences of directly releasing plasma superheated to 150 million degrees C into the natural environment might not be entirely desirable. Am I mistaken, here? Apparently, the temperatures caused by an H-bomb are quite comparable to those of the superheated plasma in a Tokamak reactor. And H-bombs are plasma bombs, by the way. So, I was thinking, this "safe and clean" energy source might just possibly have a certain down side, if you see what I mean. So, exactly how much of a down side might it have? Accidents do happen, you know. Bear in mind, the total volume of superheated plasma in the ITER Tokamak chamber will be 840 cubic meters. So, even given pressures not much greater than normal earth atmospheric pressure at sea level, this volume of vapor at 150 million degrees C., given the total failure of electromagnetic containment, would simply vaporize all surrounding buildings, and everything in the environment. What would be the total area liquidated, exactly? It shouldn't be terribly difficult to calculate it, should it?