Public information: [0] describes the six publicly-disclosed Soviet radioisotope launches up to 1989. (It's not a primary source; it's hard to find those). This one's not among them—none of the Venus missions were reported to use radioisotopes. This Kosmos 482[1] and the rest of the Soviet Venera program were publicly described as being solar-powered, which is evidence against any engineering need for other power sources. The landing probes themselves carried chemical batteries (they were very short-lived landers).

Nothing I can find through search contradicts [0]. Wikipedia's list[2] is the same, and adds two more post-1989 launches.

Seven radioisotope payloads have already reentered/crashed into Earth before—four Soviet or Russian and three American; some thermometric generators and some simple heaters; containing either polonium-210 or plutonium-238. That's not counting fission reactors, of which there are several in addition (I'm unclear the precise count of which nuclear reactors returned to Earth, or simply exploded in orbit; or what became of the latter group).

[0] https://nuke.fas.org/space/sovspace.pdf (Gary L. Bennett, "A look at the Soviet space nuclear power program" (1989))

[1] https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id... ("Two solar array wings, with an area of 2.5 meters, had a span of 4 meters. Due to the spacecraft's proximity to the Sun at Venus, the wings were only partially covered with solar cells".)

[2] https://en.wikipedia.org/wiki/List_of_nuclear_power_systems_... ("List of nuclear power systems in space")

The Pioneer probes used them to power their radios decades after launch. There aren’t real alternatives.