The availability of radioactive resources on Mars is unclear. Due to the vast effort of the nuclear enrichment process the nuclear fuel must be brought from Earth, preventing the settlement from being independent from Earth.
The maintenance effort of a legacy nuclear power station requires a huge staff. However, due to Russian plans to build a fully self-contained device on Mars the required maintenance staff comprises only 6 engineers.
Radioisotope thermoelectric generators (abbr.: RTG) are simple devices. They produce a heat difference, transformed by a thermocouple to electrical energy. The maintenance effort is low. However, RTGs do not provide enough power for a base.
Nuclear Heatpipe Reactor
Small to Medium Heatpipe Reactors offer stable safe Power that requires no outside support system or Personnel and is immune to meltdown, it can be scaled from .5kw to 50mw for remote bases, small cities, and forward operating bases here on Earth, these reactors could power a Colony or a Spaceship for between 5 and 40 years with no maintenance, with no in-situ resources needed.  
Heating greenhouses and other buildings may be done indirectly by the heat of the nuclear fission. The heat can be transported in pipes from the reactor to the buildings. Heat exchangers avoid nuclear pollution of the buildings.
- What sort of nuclear fuel is needed?
- How long can the described nuclear power stations work without replenishment of nuclear fuel?
- What is known about nuclear resources on Mars?
- Idaho National Labs, Dr. K.P Annath, Dr. Michael Kellar, Mr. James Werner, Dr James Sterbentz Portable Special Purpose Nuclear Reactor (2 MW) for Remote Operating Bases and Microgrids , https://ndiastorage.blob.core.usgovcloudapi.net/ndia/2017/power/Ananth19349.pdf, May 2017.
- NASA Kilopower Project, Dr. David Poston Small Nuclear Reactors for Mars - 21st Annual Mars Society Convention , https://www.youtube.com/watch?v=NLE5YFuCmhw, Sep 2018.