It was 2μm diameter particle. The ball-looking shape proves it was molten in high temperature and quickly cooled down. The particles contain Uranium, Zirconium etc, which are the same material as nuclear fuel and the structure inside the vessels. These were collected from 3/14 ~ 3/15/2011 in Tsukuba city Ibaraki prefecture by the study group of Science Univ. of Tokyo.
The reason why NHK suddenly started reporting about this fact is not clear. It has been already 3 years and 5 months, which is probably too late to escape. There is a possibility that NHK announces the actual contamination situation in the area closer to Tokyo when people pay much less attention to Fukushima accident.