https://www.vice.com/en_us/article/k7q7kz/nuclear-radiation-is-floating-above-northern-europe-and-nobody-knows-why

Multiple European nuclear monitoring agencies have detected higher than normal levels of radioactive isotopes in the atmosphere above Scandinavia and western Russia.

From June 22 to 23, The Comprehensive Test Ban Treaty Organization (CTBTO)—a watchdog group that operates monitoring stations to help enforce nuclear treaties—noticed elevated levels of caesium-134, caesium-137, and ruthenium-103 from its monitoring station in Sweden.