I think you're referring to the detection of radioactive iodine at trace levels in Europe back in January 2017? This made some headlines worldwide and was also covered on HN.

http://www.irsn.fr/EN/newsroom/News/Pages/20170213_Detection...

HN discussion: https://news.ycombinator.com/item?id=13676570

As far as I know, that case was never solved, and media coverage died quickly.