The plutonium 238 fuel in RTGs has a half life of 87.7 years: https://en.wikipedia.org/wiki/Plutonium-238 https://en.wikipedia.org/wiki/Plutonium-238 Uranium

The plutonium 238 fuel in RTGs has a half life of 87.7 years: https://en.wikipedia.org/wiki/Plutonium-238 https://en.wikipedia.org/wiki/Plutonium-238 Uranium 235, the fuel used in reactors, has a half life of 703.8 million years: https://en.wikipedia.org/wiki/Uranium-235 https://en.wikipedia.org/wiki/Uranium-235 This means that plutonium 238 is roughly 8 million times as radiotoxic as uranium 235, gram for gram. If this mini-reactor carries 4.5 tonnes of fuel it will be 0.012% as dangerous at launch as the power source for the Curiosity rover.