Bruce-

Thanks for the name. No one will be more delighted to offer profuse apologies if I am overstating the case.

Try reviewing this update via Wikipedia. It's the best background info I've been able to find but still very alarming to anyone who has a clue how these plants are supposed to function:
click here for update!

And I should caution that Wikipedia is only as good a "source" as whoever happens to be posting but there is a lot more detail revealed here than from the regular news reports.

The reactor building which was demolished in the explosion does not have a secondary containment system. It is an older "boiling water" reactor designed by General Electric, similar to the Vermont Yankee reactor. It was scheduled to be permanently shut down later this month.

There are six reactors on site at this nuclear plant. Three were shut down before the earthquake for regularly scheduled maintenance and thus were not available to provide back-up power after the tsunami.

The next phase of trying to cool the reactor vessel appears to be pumping sea water in, augmented with boric acid to inhibit further nuclear reaction. This is a desperate measure but is probably the best option left at this point in an attempt to avert a complete meltdown.

Charley Noble