It looks like a fire at unit #3 but it could be heavy steam rather than smoke. Still, it look like flames behind the fog/steam/smoke...
NHK has been reporting that Tepco wants to inject nitrogen in unit 3 to prevent a hydrogen explosion (see my posts). Tepco has not been able to execute the injection despite all of their efforts.
However, unit 3 has over the last few days appeared more stable, until today. It looks very bad today around 10:00 a.m Pacific time.