[vilius]

On the SE edge of the marked area Belarus is building a power plant. It is scheduled to go online July 2020 [1]. Can it be that fuel loading took place and somehow it got out and wind blew the particles towards east? (similar direction as in Chernobyl's case)

Pure speculation, but I'm Lithuanian and I'm concerned about a foreign country building a power plant 45km from my capital. CTBTO not disclosing their guess about the source makes me think it's a sensitive geopolitical matter. I just hope nothing serious has happened, but you never know with 2020.

[1] https://en.wikipedia.org/wiki/Astravets_Nuclear_Power_Plant