Why would Fission be used in a world where Fusion reactors exist?

In my world, all terrestrial bodies in the solar-system of over 900 km size have a significant human presence. Earth-moon Travel is as common as an interstate road trip, and Interplanetary travel is as common as going overseas, ranging from Venus to Earth is the same as a trip from the U.S. to U.K. today, and Earth to Pluto is the equivalent of U.S. to U.K. in 1700. This is the consequence of fusion power being mastered to the point where a fusion reactor can be stored in a truck, with reacting Deuterium, Tritium, Helium 3 and Boron 11 (of course protium fusion is still impossible, for that, feel free to build your own star). This begs the question (or rather, I beg my own question ... whatever)

Is there any practical justification for using fission power when fusion power (as described) exists?

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posted about 7 years ago

System‭

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