https://www.scientificamerican.com/article/radioactive-glass-beads-may-tell-the-terrible-tale-of-how-the-fukushima-meltdown-unfolded/

On March 14 and 15, 2011, explosions unleashed invisible radioactive plumes from the Fukushima Daiichi Nuclear Power Plant, crippled three days earlier when the strongest recorded earthquake in Japan’s history triggered a massive tsunami. As the plumes drifted over the neighboring countryside, their contents—including radioactive cesium, a by-product of the plant’s fission reactions—fell to the ground and over the ocean.

What no one knew or expected was the fallout also contained bacteria-size glassy beads, with concentrations of radioactive cesium that were far higher than those in similar-size motes of tainted dust or dirt.