A smallish chunk of Strontium-90 would safely power quite a lot of moonbase for years, as the Soviets did their remote lighthouses. Strontium-90 is the ideal radionucleide; emitting negligible gamma rays or neutrons, it just sits producing heat.
For power in the cloudtops of Venus, Titan, Saturn, Uranus, or Neptune, a full-scale nuclear reactor is as simple as a naked atomic pile hanging near the bottom of a big fabric tube with a wind turbine at the top, supported by a balloon. All the radiative output goes into heating the air around the pile, which rises and drives the wind turbine, which is the only moving part.
On the gas giants, it would have to be supported by a hot-air balloon, because the atmosphere is hydrogen.
On all four planets, surprisingly, gravity is very close to Earth-normal. (On Titan it is rather less.) Orbital velocity at the gas giants is much higher, though, so as comfortable as it might be there, it's hard to get home from them.
For power in the cloudtops of Venus, Titan, Saturn, Uranus, or Neptune, a full-scale nuclear reactor is as simple as a naked atomic pile hanging near the bottom of a big fabric tube with a wind turbine at the top, supported by a balloon. All the radiative output goes into heating the air around the pile, which rises and drives the wind turbine, which is the only moving part.
On the gas giants, it would have to be supported by a hot-air balloon, because the atmosphere is hydrogen.
On all four planets, surprisingly, gravity is very close to Earth-normal. (On Titan it is rather less.) Orbital velocity at the gas giants is much higher, though, so as comfortable as it might be there, it's hard to get home from them.