Fukushima Radioactive Seawater Computer Model

[hereonearth]

I was just trying to make sense of what was being said by those who put together that graphic. It stated, and I quote, "The computer simulation presented here is obtained by continuously releasing particles at the site during the 2 months folllowing the earthquake and then by tracing the path of these particles."

I guess I was refering to these "particles" as tracers. Sorry for my confusion on this subject. But just what did they drop in for 2 months then?