Since Sputnik, thousands of satellites have been launched into Earth orbit. In that 45 year period, only a few dozen have had radioactive payloads. They make up a tiny percentage of satellites launched.

The former Soviet Union launched 42 of their RORSAT Radar Ocean Reconnaissance satellites that had reactors on board, but the last one was launched in 1988. Two of their reactors reentered the atmosphere (Cosmos 954 and 1402) but the rest were boosted into orbits high enough that they won't decay until most of the radioactivity is gone.

The US did a few tests with satellites in the 1960s but hasn't put radioactive materials in orbit since. The reason is simple - we have solar panels powerful enough to meet our needs. The Soviet RORSAT had a powerful radar on board that required a lot of electricity, more than they could get from solar arrays.

The Apollo program had small radioactive generators (not reactors) to power the lunar experiments. One of them reentered the Earth's atmosphere with the Apollo 13 lunar module.

Since then, virtually all of the radioactive payloads have been used for interplanetary missions. One Russian Mars mission failed and the radioactive payload reentered the atmosphere in the late 1990s.