Difference between revisions of "Nuclear power"

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[[Image:nuclear_warning_sign.png|right|Nuclear Danger Icon]]
 
[[Image:nuclear_warning_sign.png|right|Nuclear Danger Icon]]
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[[File:Reactor tile.JPG|right|frameless|50x50px|link=Create a settlement]]
  
'''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]].
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'''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]].
  
 +
The [[Cost of energy on Mars|Cost of nuclear energy]] will vary with time and the colony development.  There may be periods when solar is more cost effective.  The long delays for the development of nuclear power sources may limit their availability when the first settlements are started.  The availability of nuclear fuel on Mars may be limited.
  
== Usage On Mars==
+
Nuclear reactors produce heat, that can be used by thermal engines to produce electricity, of by chemical reactions to produce hydrogen.  Leftover heat, that can range in proportion to 90% for RTG type devices down to 60% for more efficient thermal cycles, can be stored in molten salt thermal storage, or used directly to heat greenhouses, the habitat itself or industrial processes such as ice melting with Rodwells or evaporation processes.
The generation of electricity from nuclear fuel does not depend on [[environmental conditions|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.
+
==Nuclear reactor designs for Mars==
 +
There are a large number of types of nuclear reactor.  The development of nuclear reactors has also known a number of design generations, usually classified from generation 1 through generation 2 (mature designs), generation III (optimisation of generation II)  to generation 4 (currently under development) and generation 5 (future) reactors.  Most reactors considered for Mars are generation 4, as these have a high emphasis on fail safe design, simple maintenance and durability, often with decade long periods between refuelings.
  
=== Molten Salt Energy Storage ===
+
In a generation 2 Light Water Reactor, heat from the radioactive core boils [[water]] to create steam. [[turbine|Turbines]] are driven by the steam's pressure, spinning turbo generators to generate electrical energyIn a generation 4 Molten Salt Reactor, the heat generated from the core is transferred by a molten salt to a heat exchanger, that also boils water or heats an inert gas that turns a turbogeneratorThe molten salt provides opportunities of shutting down the reactor passively that do not exist for generation 2 reactors, that depend on actively moving control rods into the core of the reactor to dampen the nuclear reaction.
Molten Salt Energy Storage <ref name=":1"> Molten Salt Energy Storage, Solarreserve '' MOLTEN SALT ENERGY STORAGE '', https://www.solarreserve.com/en/technology/molten-salt-energy-storage</ref> is a process used in Concentrated Solar Thermal <ref name=":2"> Concentrated Solar Thermal, BY ROBERT DIETERICH '' Concentrated Solar Thermal '', https://apnews.com/Business%20Wire/832487eb77e04612af8bde5f7642f0f7</ref> 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<ref name=":3">Rodwell, Raul Rodriguez '' South Pole Station - Rodwells '', https://www.southpolestation.com/trivia/rodwell/rodwell.html</ref>.
 
  
=== Rodriguez Well (RODWELL)  ===
+
Although steam powered turbogenerators operating on the Rankine cycle are by far the most common type of thermal systems used to produce electricity from nuclear reactors, inert gas Brayton cycles, Stirling engines and supercritical CO2 turbines have also been identified as possible heat to electricity conversion systems.  Thermocouples have are another interesting energy conversion system, as they have no moving parts, but their low efficiency limits their use.  Heatpipes<ref name=":5">Inspired Heat-Pipe Technology,  Los Alamos '' Inspired Heat-Pipe Technology '', https://www.lanl.gov/science/NSS/issue1_2011/story6full.shtml</ref> are also heat transfer elements that might be used in future nuclear reactors.
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 <ref name=":3">Rodwell, Raul Rodriguez '' South Pole Station - Rodwells '', https://www.southpolestation.com/trivia/rodwell/rodwell.html</ref> Dr Chris Zacny has a brief on drilling RODWELLS for the Mars Society from the 21st annual Mars Society Convention https://youtu.be/NFDOrpljNAY
+
 
 +
The following types of reactors have been identified as possible models for a Mars settlement, of for vehicles on Mars.
 +
 
 +
===RTG===
 +
[[Radioisotope thermoelectric generator]]s (abbr.: RTG) are simple devices. They produce a heat difference, transformed by a [[thermocouple]] to electrical energy. The maintenance requirements are practically non existent.  However, RTGs do not provide enough power for a base, and even less for a settlement.  They also have low efficiency, in the order of 10%.  Furthermore, RTG have a nuclear core made of plutonium, and the supply for this nuclear material is extremely low<ref>https://spacenews.com/plutonium-supply-for-nasa-missions-faces-long-term-challenges/</ref>, in the order of a few kg for the entire Earth.  RTGs do have the distinction of already operating on Mars, providing power to the Curiosity rover and heating some elements of the other Mars Rovers.
 +
 
 +
===Kilopower heat pipe reactors===
 +
The Kilopower project designs are Heat-Pipe Reactors <ref name=":6">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.</ref>  that offer stable, safe power that requires no outside support system or personnel and is immune to meltdown. Their operating efficiency as electrical generators is about 23%.  They can be scaled from .5 kW to 50 MW for remote bases, small cities, and mining sites on Earth.  On Mars and in space, these reactors could power a Settlement or a Spaceship for between 5 to 40 years with no maintenance except replacement of the Sterling engines and with no in-situ resources needed. Heatpipe Reactors are inherently safe.  If no energy is removed, the system stabilizes to a constant temperature that is below the melting temperature of the components, so it will not melt down or change state.<ref name=":7">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</ref> <ref name=":8">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.</ref> <ref name=":9">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.</ref>  The heatpipes are used to transfer heat from the core to the gas running through the Sterling engines.  The fluid in the heat pipes moves by capillarity, so these have no moving parts, increasing reliability.
 +
 
 +
However, these reactors do have secondary systems, such as Sterling engines, connected to generators to produce electric power, and radiators to dissipate excess heat.  These add to the mass of the reactor, making the system somewhat less advantageous.  The kilopower reactors use enriched uranium<sup>235</sup> that is cast into a solid steel core.  This nuclear fuel  is unlikely to be available on Mars and will need to be imported from Earth.
 +
 
 +
===Molten Salt Reactors===
 +
Molten Salt Reactors use a liquid salt coolant that extracts energy from a nuclear fuel, that can be a liquid or a solid. The cooling salt is usually at atmospheric pressure, as opposed to a conventional reactor that uses high pressure water as a cooling agent.  The high pressure water represents an explosion risk if it overheats beyond the capacity of the pipes that hold it.  In contrast, if the molten salt temperature rises too much, it will expand and separate the suspended nuclear fuel particles, slowing the nuclear  reaction.  As an added safety feature, some designs have, at the lowest point in the core, an opening that is kept shut by an externally cooled plug of frozen salt.  If for any reason the external source of cooling is lost, the plug melts and the liquid salt contents of the core are dumped into a storage tank, where the salt is separated by a graphite moderator into a number of compartments.  The salt becomes sub-critical and cools down. In the  event of a leak, 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 <ref name=":10">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.</ref> <ref name=":11">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.</ref>.  Most molten salt reactors use enriched uranium<sup>235</sup>  or Thorium as fuel.
 +
 
 +
==Operations==
 +
Nuclear reactors require fuel that eventually needs to be replaced.  Generation 4 designs for small nuclear reactor often include fuel for ten to twenty years of operation, operating as a form of nuclear battery. 
 +
Nuclear reactors often operate at high temperatures and have secondary systems that are subject to wear.  Most existing designs require well trained operators and considerable support staff for maintenance.  Reactors designed for Space and Mars will need to have mostly hands off operations.
 +
 
 +
Reactors produce heat, that is converted at an efficiency of 25 to 40% depending on the design.  The rest of the heat needs to be removed and dissipated into the environment using radiators.  These add mass to the system as well as potential leak points.
 +
 
 +
The nuclear fuel is a very small part of the entire reactor power producing system.  Most of the mass is in the containment, piping, generators and radiators.
 +
 
 +
The transportation of nuclear fuel to Mars should be simple and safe.  However, there is significant opposition to nuclear energy in civil society that needs to be taken into account when a nuclear system is chosen. 
 +
==Usage On Mars==
 +
 
 +
===Electrical power===
 +
The generation of electricity from nuclear fuel does not depend on [[environmental conditions|weather conditions]] so would be useful for maintaining a reliable source of power on Mars. Thorium is available on Mars in large, low concentration, deposits at Mid latitudes.  This is the preferred fuel in Molten Salt Reactors, particularly Liquid Fuel Thorium Reactors LFTRs.
 +
 
 +
Most nuclear reactors designs have a thermal efficiency of about 35%.  This means 35% of the heat from the core can be turned into electricity, the rest needs to be dissipated as low grade heat into the environment. This makes nuclear reactors useful for combined services, where electricity and heat can be used by a settlement.
 +
 
 +
Nuclear reactors might be required during long dust storms, when the power from solar arrays could dip low enough to endanger a solar powered colony.
  
== Nuclear reactor ==
+
====Supercritical CO2 Turbines====
In a Light Water Reactor, heat caused by the radioactivity boils [[water]] to steam. [[turbine|Turbines]] are driven by the steam's pressure, spinning a dynamo to generate electric energyIn 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 at separate locations in the colony.
+
Supercritical CO2 Turbines use high pressure CO2 to drive a small turbine and compressor system at high efficency to generate powerCombined with a Liquid Fuel Thorium Reactor, a unit the size of a desk might generate 10 MW of power. <ref name=":4">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</ref>
  
== Nuclear heating ==
+
===Heat generation===
Heating [[greenhouse]]s and other [[building]]s 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.
+
Heating [[greenhouse]]s and other [[building]]s may be done indirectly by the waste heat of the nuclear fission. The heat can be transported in pipes from the reactor to the buildings. Heat exchangers avoid radiation pollution of the buildings.
  
== Types of Nuclear Generation ==
+
====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 <ref name=":3">Rodwell, Raul Rodriguez '' South Pole Station - Rodwells '', https://www.southpolestation.com/trivia/rodwell/rodwell.html</ref> Dr Chris Zacny has a brief on drilling RODWELLS for the Mars Society from the 21st annual Mars Society Convention https://youtu.be/NFDOrpljNAY
  
=== RTG ===
+
Waste heat from nuclear reactor cooling could be used to melt ice in this type of wells.
[[Radioisotope thermoelectric generator]]s (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 ===
+
====Molten Salt Energy Storage====
Megawatt Level Heat-Pipe Reactors <ref name=":4"> 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.</ref>  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.<ref name=":5"> 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</ref> <ref name=":6">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.</ref> <ref name=":7">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.</ref>
+
Molten Salt Energy Storage <ref name=":1">Molten Salt Energy Storage, Solarreserve '' MOLTEN SALT ENERGY STORAGE '', https://www.solarreserve.com/en/technology/molten-salt-energy-storage</ref>  is a process used in Concentrated Solar Thermal <ref name=":2">Concentrated Solar Thermal, BY ROBERT DIETERICH '' Concentrated Solar Thermal '', https://apnews.com/Business%20Wire/832487eb77e04612af8bde5f7642f0f7</ref> 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<ref name=":3" />. However, the mass of the molten salts is high and the amount required might be prohibitive. It may prove more economical to use the waste heat from an operating reactor directly, as nuclear reactors are the most efficient when they operate continuously.
  
=== Molten Salt Reactor ===
+
==Nuclear Fuel Sources on Mars==
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 <ref name=":8"> 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.</ref> <ref name=":9"> 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.</ref>
 
  
== Nuclear Fuel Sources on Mars ==
+
===Thorium Deposits on Mars===
 +
JPL has identified areas of high Thorium concentration on Mars.  This is the preferred fuel in a number of Molten Salt Reactor designs. <ref name=":12">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.</ref>
  
=== Thorium Deposits on Mars ===
+
However, it is important to note that high concentration in this case means 1ppm, and that common soil on Earth has a Thorium 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 ore deposits that might be mined in an economical way.
JPL has identified Thorium deposits on Mars, this is the preferred fuel in a number of Molten Salt Reactor designs. <ref name=":10"> Map of Martian Thorium at Mid-LatitudesJPL '' Map of Martian Thorium at Mid-Latitudes '', https://www.jpl.nasa.gov/spaceimages/details.php?id=PIA04257, March 2003.</ref>
 
  
== Open issues ==
+
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?
+
The production of enriched nuclear fuel required for most designs complicates the case for in-situ production of nuclear fuel.
*How long can the described nuclear power stations work without replenishment of nuclear fuel?
 
*What is known about nuclear resources on Mars?
 
  
== References ==
+
==References==
 
{{reflist}}
 
{{reflist}}
  
== External links ==
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==External links==
  
* None
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*None
  
 
[[Category:Sources]]
 
[[Category:Sources]]

Revision as of 08:17, 2 August 2019

Nuclear Danger Icon
Reactor tile.JPG

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.

The Cost of nuclear energy will vary with time and the colony development. There may be periods when solar is more cost effective. The long delays for the development of nuclear power sources may limit their availability when the first settlements are started. The availability of nuclear fuel on Mars may be limited.

Nuclear reactors produce heat, that can be used by thermal engines to produce electricity, of by chemical reactions to produce hydrogen. Leftover heat, that can range in proportion to 90% for RTG type devices down to 60% for more efficient thermal cycles, can be stored in molten salt thermal storage, or used directly to heat greenhouses, the habitat itself or industrial processes such as ice melting with Rodwells or evaporation processes.

Nuclear reactor designs for Mars

There are a large number of types of nuclear reactor. The development of nuclear reactors has also known a number of design generations, usually classified from generation 1 through generation 2 (mature designs), generation III (optimisation of generation II) to generation 4 (currently under development) and generation 5 (future) reactors. Most reactors considered for Mars are generation 4, as these have a high emphasis on fail safe design, simple maintenance and durability, often with decade long periods between refuelings.

In a generation 2 Light Water Reactor, heat from the radioactive core boils water to create steam. Turbines are driven by the steam's pressure, spinning turbo generators to generate electrical energy. In a generation 4 Molten Salt Reactor, the heat generated from the core is transferred by a molten salt to a heat exchanger, that also boils water or heats an inert gas that turns a turbogenerator. The molten salt provides opportunities of shutting down the reactor passively that do not exist for generation 2 reactors, that depend on actively moving control rods into the core of the reactor to dampen the nuclear reaction.

Although steam powered turbogenerators operating on the Rankine cycle are by far the most common type of thermal systems used to produce electricity from nuclear reactors, inert gas Brayton cycles, Stirling engines and supercritical CO2 turbines have also been identified as possible heat to electricity conversion systems. Thermocouples have are another interesting energy conversion system, as they have no moving parts, but their low efficiency limits their use. Heatpipes[1] are also heat transfer elements that might be used in future nuclear reactors.

The following types of reactors have been identified as possible models for a Mars settlement, of for vehicles on Mars.

RTG

Radioisotope thermoelectric generators (abbr.: RTG) are simple devices. They produce a heat difference, transformed by a thermocouple to electrical energy. The maintenance requirements are practically non existent. However, RTGs do not provide enough power for a base, and even less for a settlement. They also have low efficiency, in the order of 10%. Furthermore, RTG have a nuclear core made of plutonium, and the supply for this nuclear material is extremely low[2], in the order of a few kg for the entire Earth. RTGs do have the distinction of already operating on Mars, providing power to the Curiosity rover and heating some elements of the other Mars Rovers.

Kilopower heat pipe reactors

The Kilopower project designs are Heat-Pipe Reactors [3] that offer stable, safe power that requires no outside support system or personnel and is immune to meltdown. Their operating efficiency as electrical generators is about 23%. They can be scaled from .5 kW to 50 MW for remote bases, small cities, and mining sites on Earth. On Mars and in space, these reactors could power a Settlement or a Spaceship for between 5 to 40 years with no maintenance except replacement of the Sterling engines and with no in-situ resources needed. Heatpipe Reactors are inherently safe. If no energy is removed, the system stabilizes to a constant temperature that is below the melting temperature of the components, so it will not melt down or change state.[4] [5] [6] The heatpipes are used to transfer heat from the core to the gas running through the Sterling engines. The fluid in the heat pipes moves by capillarity, so these have no moving parts, increasing reliability.

However, these reactors do have secondary systems, such as Sterling engines, connected to generators to produce electric power, and radiators to dissipate excess heat. These add to the mass of the reactor, making the system somewhat less advantageous. The kilopower reactors use enriched uranium235 that is cast into a solid steel core. This nuclear fuel is unlikely to be available on Mars and will need to be imported from Earth.

Molten Salt Reactors

Molten Salt Reactors use a liquid salt coolant that extracts energy from a nuclear fuel, that can be a liquid or a solid. The cooling salt is usually at atmospheric pressure, as opposed to a conventional reactor that uses high pressure water as a cooling agent. The high pressure water represents an explosion risk if it overheats beyond the capacity of the pipes that hold it. In contrast, if the molten salt temperature rises too much, it will expand and separate the suspended nuclear fuel particles, slowing the nuclear reaction. As an added safety feature, some designs have, at the lowest point in the core, an opening that is kept shut by an externally cooled plug of frozen salt. If for any reason the external source of cooling is lost, the plug melts and the liquid salt contents of the core are dumped into a storage tank, where the salt is separated by a graphite moderator into a number of compartments. The salt becomes sub-critical and cools down. In the event of a leak, 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 [7] [8]. Most molten salt reactors use enriched uranium235 or Thorium as fuel.

Operations

Nuclear reactors require fuel that eventually needs to be replaced. Generation 4 designs for small nuclear reactor often include fuel for ten to twenty years of operation, operating as a form of nuclear battery. Nuclear reactors often operate at high temperatures and have secondary systems that are subject to wear. Most existing designs require well trained operators and considerable support staff for maintenance. Reactors designed for Space and Mars will need to have mostly hands off operations.

Reactors produce heat, that is converted at an efficiency of 25 to 40% depending on the design. The rest of the heat needs to be removed and dissipated into the environment using radiators. These add mass to the system as well as potential leak points.

The nuclear fuel is a very small part of the entire reactor power producing system. Most of the mass is in the containment, piping, generators and radiators.

The transportation of nuclear fuel to Mars should be simple and safe. However, there is significant opposition to nuclear energy in civil society that needs to be taken into account when a nuclear system is chosen.

Usage On Mars

Electrical power

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, low concentration, deposits at Mid latitudes. This is the preferred fuel in Molten Salt Reactors, particularly Liquid Fuel Thorium Reactors LFTRs.

Most nuclear reactors designs have a thermal efficiency of about 35%. This means 35% of the heat from the core can be turned into electricity, the rest needs to be dissipated as low grade heat into the environment. This makes nuclear reactors useful for combined services, where electricity and heat can be used by a settlement.

Nuclear reactors might be required during long dust storms, when the power from solar arrays could dip low enough to endanger a solar powered colony.

Supercritical CO2 Turbines

Supercritical CO2 Turbines use high pressure CO2 to drive a small turbine and compressor system at high efficency to generate power. Combined with a Liquid Fuel Thorium Reactor, a unit the size of a desk might generate 10 MW of power. [9]

Heat generation

Heating greenhouses and other buildings may be done indirectly by the waste heat of the nuclear fission. The heat can be transported in pipes from the reactor to the buildings. Heat exchangers avoid radiation pollution of the buildings.

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 [10] Dr Chris Zacny has a brief on drilling RODWELLS for the Mars Society from the 21st annual Mars Society Convention https://youtu.be/NFDOrpljNAY

Waste heat from nuclear reactor cooling could be used to melt ice in this type of wells.

Molten Salt Energy Storage

Molten Salt Energy Storage [11] is a process used in Concentrated Solar Thermal [12] 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[10]. However, the mass of the molten salts is high and the amount required might be prohibitive. It may prove more economical to use the waste heat from an operating reactor directly, as nuclear reactors are the most efficient when they operate continuously.

Nuclear Fuel Sources on Mars

Thorium Deposits on Mars

JPL has identified areas of high Thorium concentration on Mars. This is the preferred fuel in a number of Molten Salt Reactor designs. [13]

However, it is important to note that high concentration in this case means 1ppm, and that common soil on Earth has a Thorium 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 ore deposits 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.

The production of enriched nuclear fuel required for most designs complicates the case for in-situ production of nuclear fuel.

References

  1. Inspired Heat-Pipe Technology, Los Alamos Inspired Heat-Pipe Technology , https://www.lanl.gov/science/NSS/issue1_2011/story6full.shtml
  2. https://spacenews.com/plutonium-supply-for-nasa-missions-faces-long-term-challenges/
  3. 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.
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  5. 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.
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External links

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