I would point out that the dangerous stuff that is there is iodine(-131 IIRC) with a half life of 8 days and since it can give you thyroid cancer it is not "safe" until it virtually is gone at 80 days; and cesium-137 with a half life of 30 years, a gram of which can kill you.
Right. Most of the radiologicals that have been released with the steam have very short half lives so the radiation levels drop rapidly (relatively speaking).
Time.