Is Fukushima now more serious than the 1979 Three Mile Island incident in the U.S.A., as US Energy Secretary Steven Chu recently claimed?     Hard to say yet.  But a mysterious rise in radiation Wednesday is certainly cause for concern.   It seems to have been big enough to force technicians to leave the plant, according to the BBC.  Over the days of the Fukushima crisis, attention has switched from reactor building 1 to 3, to 2, back to 3 - and now, to 4.

"The possibility of re-criticality is not zero" is a high level of concern to a nuclear power plant.  Until the situation in reactor 4 is known, the most important task remains to get enough water flowing into reactors 1, 2 and 3 to cool the cores.