So, it seems to come from nuclear fission, likely of civilian origin, and perhaps originating from fuel elements: > The Netherland's public health agency said

So, it seems to come from nuclear fission, likely of civilian origin, and perhaps originating from fuel elements: > The Netherland's public health agency said Friday it analysis of Nordic data showed that radionuclides had come "from the direction of Western Russia," indicating "damage to a fuel element in a nuclear power plant." > On Friday, the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) tweeted that its sensors had detected "harmless" isotopes, identified as Caesium 137, Caesium 134, and Ruthenium 103, "very much probably of civilian origin." > > According to the UN's International Atomic Energy Agency based in Vienna, Western Europe has 108 reactors and Central and Eastern Europe 73 reactors. https://www.dw.com/en/slight-radioactivity-rise-in-nordic-countries/a-53968555 https://www.dw.com/en/slight-radioactivity-rise-in-nordic-co... The presence uf Ruthenium-103 indicates that these are fresh fission products because it has a half-life of only 39 days (https://en.wikipedia.org/wiki/Isotopes_of_ruthenium https://en.wikipedia.org/wiki/Isotopes_of_ruthenium). So, it is not impossible that it is a leak in a civil reactor.