Nuclear fuel reprocessing plants release iodine into the atmosphere. The prevailing wind direction at European latitudes is west to east, so when the iodine comes back down in rain, it'll likely do so over Russia (emptying into the Arctic Ocean), Central Asia (emptying into the Caspian Sea and various lakes) or Northeast Asia (emptying into the nortwestern Pacific Ocean, including the Yellow Sea.) This paper has an illustration: https://www.sciencedirect.com/science/article/abs/pii/S03043...