The USSR sprinkled more than 2,500 RTGs (small highly-radioactive generators) across the Arctic and in remote mountain locations. They are unsupervised and unmaintained, stolen and scrapped by metal dealers who sometimes die of radiation poisoning.

https://www.gizmodo.com.au/2023/06/the-ussr-sprinkled-more-than-2500-nuclear-generators-across-the-countryside/