As far as I know, the safety record on nuclear subs is pretty good compared to the commercial nuclear power industry. But subs if the unthinkable happened, likely would go down to the bottom of the ocean and more likely than not, keep the accident fairly contained.
The worry with reactors in space has been that an accident would cause contamination of the Earth or some other planet or be dangerous to the crew. The risks of that happening, although small have been significantly worrisome to prevent the US's use of them except for exceptional purposes.
See
https://en.wikipedia.org/wiki/SNAP-10ANote what happened to it and the fact that there is debris of it in space orbiting the Earth now.
The Russians have used small nuclear power plants in space more than the US.
Nothing has changed. No magical new technology has suddenly emerged. Also, because of the ready availability of solar energy, most of the needs of space based hardware are met perfectly well by solar cells. Keep in mind that as radio signals travel line of sight, a quite low power transmitter on a satellite can be received over large portions of the Earth.
Since RF spectrum in space is a finite resource it makes more sense to use highly directional antennas and low power.
But when we leave the Earth - especially go farther away from the Sun the amount of solar power available declines. Also, as you go towards the poles in a place like Mars the same things happen there that happen here, less solar power is available. Mars also has dust storms.