Nuclear Power is a method of energy generation. It uses nuclear fuel to produce heat, which is usually transformed into electricity. Nuclear power is considered the preferred energy source for most plans for medium- to long-term human expeditions to Mars.
- 1 Usage On Mars
- 2 Nuclear reactor
- 3 Nuclear heating
- 4 Types of Nuclear Generation
- 5 Nuclear Fuel Sources on Mars
- 6 Open issues
- 7 References
- 8 External links
Usage On Mars
The generation of electricity from nuclear fuel does not depend on weather conditions so would be useful for maintaining a reliable source of power on Mars. Thorium is available on Mars in large deposits at Mid latitudes, this is the preferred fuel in Molten Salt Reactors particularly Liquid Fuel Thorium Reactors LFTRs.
Molten Salt Energy Storage
Molten Salt Energy Storage  is a process used in Concentrated Solar Thermal  that allows storing large amounts of heat energy in the form of high temperature molten salt. This reserve can be tapped for direct use in colony heating, Evaporative water purification, and Rodriguez Wells.
Rodriguez Well (RODWELL)
RODWELLS Are a form of well melted into Antarctic Ice to provide a constant source of water for use on a base, this lowers a heat source deep into the ice melting an area of ice that is partially pumped out as the ice cave grows  Dr Chris Zacny has a brief on drilling RODWELLS for the Mars Society from the 21st annual Mars Society Convention https://youtu.be/NFDOrpljNAY
Supercritical CO2 Turbines
Supercritical CO2 Turbines, use high pressure CO2 to drive a turbine engine at high efficency to generate power, combined with a Liquid Fuel Thorium Reactor a unit the size of a desk can generate 10mw of energy. 
In a Light Water Reactor, heat caused by the radioactivity boils water to steam. Turbines are driven by the steam's pressure, spinning a dynamo to generate electric energy. In a Molten Salt Reactor the heat generated from the core is redirected for use in Molten Salt Thermal Storage, structural heating, Stirling Generators to provide electricity, Evaporative Water Purification, and to melt water in RODWELLS. In a Heatpipe reactor a solid core generates heat that is transferred via "Heatpipe" technology to Stirling Generators with the option to transfer the heat tp Molten Salt Storage for further direct heat energy use or Stirling Generators or Supercritical CO2 Turbines at separate locations in the colony.
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.
Types of Nuclear Generation
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
Megawatt Level Heat-Pipe 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. Heatpipe Reactors are inherently stable meaning if no energy is removed as heat the system stabilises to a constant temperature. Heat-Pipe Reactors are inherently "Walk-Away Safe" meaning if an emergency happens and the reactor is left alone it will not melt down or change state.  
Molten Salt Reactor
Molten Salt Reactors use a liquid salt fuel that suspends a nuclear fuel in the salt at atmospheric pressure as opposed to a solid fuel reactor that uses high pressure water as a cooling agent that can turn into a steam explosion. If the salt temperature rises it will separate the suspended nuclear fuel and slow the reaction, as a safety feature at the lowest point in the core a pipe is cooled forcing the salt in that section of pipe to freeze and create a plug of salt, if that external cooling is lost the plug melts and the liquid salt contents of the core dump into a storage tank, when the salt is separated from the graphite moderator the salt becomes sub-critical and cools down. In the unlikely event of a leak of the Salt solidifies quickly allowing for far easier cleanup vs liquid water seeping into the environment. Since no pressurized steam is involved there is no need for a large domed pressure building around the core. For a more detailed explanation from Dr. Kirk Sorensen please see https://youtu.be/D3rL08J7fDA  
Nuclear Fuel Sources on Mars
Thorium Deposits on Mars
JPL has identified Thorium deposits on Mars, this is the preferred fuel in a number of Molten Salt Reactor designs. 
However, it is important to note that high concentration in this case means 1ppm, and that common soil on Earth has a concentration of 6ppm. There are granitic deposits on Earth with Thorium concentrations of 56ppm, that are considered very low grade resources. There is no evidence yet of thorium ores that might be mined in an economical way.
In general, Thorium maps made from Mars Odyssey data suggest that the martian crust is poor in Thorium or uranium. It is possible that this reflects a formation model for Mars that would be much poorer in heavy metals than for Earth, and that Mars might have formed with more volatiles. This might be an explanation for Mars' lower density compared to Earth, 3.95 tonnes per m3 (g/cm3) vs 5,51 tonnes per m3 (g/cm3) for Earth.
- 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?
- Molten Salt Energy Storage, Solarreserve MOLTEN SALT ENERGY STORAGE , https://www.solarreserve.com/en/technology/molten-salt-energy-storage
- Concentrated Solar Thermal, BY ROBERT DIETERICH Concentrated Solar Thermal , https://apnews.com/Business%20Wire/832487eb77e04612af8bde5f7642f0f7
- Rodwell, Raul Rodriguez South Pole Station - Rodwells , https://www.southpolestation.com/trivia/rodwell/rodwell.html
- Supercritical CO2: The Path to Less-Expensive, “Greener” Energy, Machine Design Supercritical CO2: The Path to Less-Expensive, “Greener” Energy , https://www.machinedesign.com/mechanical/supercritical-co2-path-less-expensive-greener-energy
- Inspired Heat-Pipe Technology, Los Alamos Inspired Heat-Pipe Technology , https://www.lanl.gov/science/NSS/issue1_2011/story6full.shtml
- Megawatt Level Heat-Pipe Reactors, Mcclure, Patrick Ray Poston, David Irvin Dasari, Venkateswara Rao Reid, Robert Stowers DESIGN OF MEGAWATT POWER LEVEL HEAT PIPE REACTORS , https://permalink.lanl.gov/object/tr?what=info:lanl-repo/lareport/LA-UR-15-28840, Nov 2015.
- Solid-Core Heat-Pipe Nuclear Battery Type Reactor, Ehud Greenspan Solid-Core Heat-Pipe Nuclear Battery Type Reactor , https://www.osti.gov/servlets/purl/940911
- 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.
- Safety assessment of molten salt reactors in comparison with light water reactors, Badawy M.Elsheikh Safety assessment of molten salt reactors in comparison with light water reactors , https://www.sciencedirect.com/science/article/pii/S1687850713000101, Oct, 2013.
- How Molten Salt Reactors Might Spell a Nuclear Energy Revolution, Stephen Williams How Molten Salt Reactors Might Spell a Nuclear Energy Revolution , https://www.zmescience.com/ecology/what-is-molten-salt-reactor-424343/, Feb 2019.
- Map of Martian Thorium at Mid-Latitudes, JPL Map of Martian Thorium at Mid-Latitudes , https://www.jpl.nasa.gov/spaceimages/details.php?id=PIA04257, March 2003.