Last year was a release at a Norwegian research reactor. First of all, that was an impressive feat of analytical chemistry, that they could detect a fairly insignificant leak all over Europe.

http://www.world-nuclear-news.org/RS-Radioactive-release-for...

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.