The Russians are using thermopiles driven by radioactive decay, not actual reactors that go critical. Such devices are indeed quite stable for decades unless they get targeted by scrappers. A few hundred watts from a large RTG is a drop in the bucket compared to the power required to keep a base going, so those aren't applicable.

If you need a transmitter or relay station hundreds of miles from people to run for years without fueling... RTGs are an option for governments.