People who keep an eye on the Fukushima Daiichi weathercam have often claimed "massive fires" or "massive steam releases" from the reactors which are easily explained as fog, clouds, or low-light-level camera noise
However, this video http://t.co/wa9KXinD
, recorded yesterday (feb 28), apparently shows a substantial release of steam from the ground near units 3 and 4, starting at ~00:38. It does not seem to be fog (too low, very localized and persistent). It does not seem to be smoke (disappears instead of just dispersing).
I cannot imagine what that "steam" could be. AFAIK the water processing plant does not use steam. The reactors and basement water should be too cool. I cannot think of a cleaning or maintenance activity that would use steam. Any explanations?