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#51 2018-06-17 05:26:46

kbd512
Administrator
Registered: 2015-01-02
Posts: 6,205

Re: Magnox Nuclear Reactors for Mars

Louis,

There are no mines to provide the raw materials for solar panels on Mars.  Whether you import nearly ready-to-use solar panels or fission reactors from Earth, or spend years setting up the machinery to manufacture either on Mars using raw materials that are imported from Earth, you're still 100% dependent on energy production technology imported from Earth.  No factories on Earth are set up in a day, a week, a month, or even a year.  Simply designing the factory takes a year or more in most cases.  On top of that, all raw materials and manpower that required to produce the finished products are readily available on Earth.

Go read about how long it takes to set up a factory to do anything here on Earth.  Tesla still can't produce cars at their target rate with all the resources available to them.  The manufacture of batteries and solar panels is not easy or simple and it's extraordinarily resource and manpower intensive.  The colonists on Mars need to produce their own air, water, food, and textiles using equipment imported from Earth.  That is the single most important step for permanent colonization.  The second step required is to produce the construction materials on Mars, which is mostly concrete / steel / glass.  Several decades later, the importation of electrical equipment from Earth will become cost prohibitive.

The major difference between solar panels and batteries or fission reactors are that as the power requirements to support activities like food production, mining, and manufacturing increase d, nuclear power requires a lot less resource importation to operate and provides reliable power.  Here on Earth, fission reactors are operational 90% of the time or better and output levels of 90% of rated capacity or better.  There is not one single solar power plant on Earth that has ever achieved rated capacity, nor will there ever be, and we're 50% closer to the giant fusion reactor that supplies the solar power.  The real only argument between solar and fission power advocates seems to be which nuclear reactor to use and how close it should be sited to the point of use.

Some of us want to fly in small fission reactors and spend the rest of our time on useful activities like finding available natural resources, propellant production to get our spaceships back so we can use them to ship more stuff to Mars, air / water / food production to sustain the colonists living on Mars, and collecting or mining raw materials so we can build more habitable structures to put more people on Mars.  We're not particularly enamored with the idea of tending to solar arrays and batteries and would rather have robots spend their time knocking the dust off the arrays so we continue to use opportunistic solar power when it's available.  We want to drop a few nukes in hand-dug bore holes, connect the power cables, turn 'em on, and start making 24/7 electrical power so we can spend the rest of our time building giant solar farms, digging giant bore holes for people / animals / food crops to live in, and the never ending list of other tasks that need to be done.

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#52 2020-09-18 15:18:16

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 26,734

Re: Magnox Nuclear Reactors for Mars

bump

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#53 2022-06-03 08:36:46

Mars_B4_Moon
Member
Registered: 2006-03-23
Posts: 4,782

Re: Magnox Nuclear Reactors for Mars

Idaho Strategic Resources Adds the Lemhi Pass Project - The Largest Known Concentration of Thorium Resources in the United States
https://www.yahoo.com/news/idaho-strate … 00562.html

ANEEL fuel, a uranium-thorium mixture, Th-232 captures a neutron becomes Th-233 eventually U-233,  decay product Pa-233 if it grabs another neutron before decaying to U-233, it becomes Pa-234 which decays to non-fissile U-234  with higher flux more likely you are to get U-234 instead of U-233.  Some new innovative manufacturing happening and the Chinese are doing something also but little info has gone public.

https://www.forbes.com/sites/jamesconca … lear-fuel/

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#54 2022-09-14 06:22:23

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 2,210

Re: Magnox Nuclear Reactors for Mars

A technical description of Magnox reactors.
https://inis.iaea.org/collection/NCLCol … 052480.pdf

These reactors had the advantage of using natural uranium fuel, requiring no enrichment.  The fuel was in the form of solid uranium metal bars, 1" thick, clad in magnesium alloy.  The plants were very reliable and safe, low power density made them meltdown proof.

The downsides were: (1) The need for a large, low power density graphite moderator block to moderate neutrons; (2) The thermal efficiency was low - 30% max, because the fuel operating temperature was constrained by the low melting point of magnesium; (3) With natural uranium fuel, peak burnup was low.  This meant a relatively high fuel throughput, which generated high volumes of spent fuel; (4) The low density of CO2 coolant required large external steel boilers to generate steam.  In some plants these boilers suffered badly from corrosion.

In spite of its problems, this is a reactor type that we could build relatively early on Mars.  It's construction is really dominated by plain carbon steels, graphite and concrete.  These are some of the first materials that will be produced in abundance on Mars.  The North Koreans have developed native Magnox to support their weapons programme.  Out of all reactor types, this is the easiest to build on a tight budget, with limited available materials.  Calder Hall was the world's first commercial nuclear power plant.  It generated 60MW of electric power, with some 50MW going onto the grid.  Each reactor, with shielding, weighed some 33,000 tonnes.  The moderator block at 9.5m in diameter (with the relector increasing diameter to 11.5m) was close to minimum critical diameter for natural uranium and graphite.

Whether we will build these or some sort of water based reactor to support a growing Mars base, is a decision that Musk and others will have to make.

Last edited by Calliban (2022-09-14 06:32:52)


"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."

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#55 2022-09-24 04:26:05

Mars_B4_Moon
Member
Registered: 2006-03-23
Posts: 4,782

Re: Magnox Nuclear Reactors for Mars

China's Moon Mission Uncovers A New Lunar Mineral And Rare Fusion Reactor Fuel
https://hothardware.com/news/chinas-moo … actor-fuel

Small Nuclear Reactors Emerge as Energy Option, but Risks Loom
https://www.bignewsnetwork.com/news/272 … risks-loom

Efforts to Transform US Nuclear Industry Entering Full Bloom
https://www.aip.org/fyi/2022/efforts-tr … full-bloom

small-scale reactors could provide power to astronauts exploring the surface of the Moon and eventually Mars

A Primordial Atmospheric Origin Of Hydrospheric Deuterium Enrichment On Mars
https://astrobiology.com/2022/09/a-prim … -mars.html

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#56 2022-09-27 11:14:55

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 2,210

Re: Magnox Nuclear Reactors for Mars

Graphite moderated, natural uranium fuelled reactors, would be a more practical option if they were developed as pressure tube reactors.  Neutrons have a long slowing down length in graphite, making the minimal critical size of a graphite moderated, natural U reactor, at least 9m in diameter.  The large graphite core is a problem if it needs to be embedded within a high pressure vessel.  That pressure vessel becomes a huge, high cost component.

The reason that the Soviets continued building RBMK reactors for as long as they did, was that these reactors were pressure tube, boiling water reactors.  They were easy to build and maintain, because they did not require bulky, thick walled pressure vessels.  The graphite moderator was contained in a gas cooling circuit, with water filled pressure tubes (containing fuel assemblies) running through it.  To build a bigger reactor, you just increased the diameter of the graphite moderator block and ran more pressure tubes through it.  The fuel did not require high enrichment, which also made it cheap.  This allowed the Soviets to build RBMK reactors cheaply and quickly, at power levels up to 1500MWe, with plans to construct units up to 2400MWe.  This was enormously powerful for the time and even today.

The original British gas cooled reactors could not function as pressure tube reactors.  Steel pressure tubes would have absorbed too many neutrons.  Aluminium or magnesium wouod have been problematic because of their poor creep properties and high coefficient of thermal expansion.  For this concept to work, zirconium alloys are needed for pressure tubes, which weren't available to the British in the 1950s or 1960s.  Assuming that zircalloy tubes can be imported to Mars, pressure tube gas-cooled reactors could be a cheap and speedy way of building up reactor capacity.  Both the moderator and pressure tubes would be cooled with carbon dioxide.  The moderator envelope would be pressurised to about 1bar.

The pressure within the pressure tubes would depend on the cycle used.  For a steam cycle, pressure tubes would connect to a circular carbon steel ring tube around the top of the core, with a similar arrangement at the bottom.  Gas ducts would exit the top ring and pass through boilers, before entering a blower that discharges in the bottom ring.  In Magnox reactors, gas circuit pressure was 7-22 bar.  Alternatively, a direct cycle S-CO2 power generation loop could be used.  Carbon dioxide would pass through the pressure tubes and into a similar ring tube, but the gas ducts would directly feed an CO2 gas turbine.  Wylfa, the last and most advanced Magnox reactor, achieved an outlet temperature of 410°C.  Higher temperatures are possible if the magnesium alloy cladding is replaced with zircalloy, which has a much higher melting point.  The efficiency of an S-CO2 cycle with a 410°C inlet temperature could be as high as 40%, but this will depend upon the primary circuit pressure, which needs to be as high as possible to reduce pumping power requirements.  The MIT baseline was 20MPa, but the Japanese designed an S-CO2 direct cycle gas cooled reactor with an operating pressure of 7MPa (70 bar).  This is probably more realistic given that pressure tubes are parasitic neutron absorbers.

The S-CO2 option is particularly interesting, because it allows the power generating equipment to be relatively compact compared to a steam cycle.  It also allows the elimination of primary boilers, which are huge components in a gas cooled reactor and are subject to corrosion issues.  A direct cycle, S-CO2 cooled, pressure tube reactor, achieves all of the advantages of the old Soviet RBMK reactors, without any of their inherent safety problems.  Like the RBMK, they can be scaled up to almost any size without any engineering problems introduced by pressure vessels.  Like the RBMK, they are direct cycle without the requirement for primary heat exchangers.  They can run on natural uranium mined on Mars.  That is something RBMK reactors could not do, at least not safely.

Wylfa was able to to achieve a core power density of 0.86MW/m3.  This is about double the power density of the Calder Hall reactors, but is only about 1% of the core power density of a modern pressurised water reactor and only 2% of a BWR.  However, the use of pressure tubes would allow the great bulk the graphite moderator to be only lightly pressurised.  The moderator envelope could be reinforced concrete and would also serve the function of biological shield for the reactor.  On Mars, we could build these reactors underground and use soil pressure to provide the relatively small amount of back pressure needed for the moderator cooling circuit.  Martian soil is highly basic.  Mixing it with water will provide a cement like substance with high strength once dried.

The decay heat strategy for such a reactor is relatively simple, because the graphite moderator has enormous heat capacity.  Standard heat removal would use the blowers to dump heat into the power cycle heat exchangers.  These would provide redundancy, as the reactor would have more than one power generation loop.  But the huge graphite core is both an efficient heat store and radiator.  A 17.4m wide and 9.2m high graphite moderator block (i.e wylfa) heated to 500°C, will radiate some 20MW of heat.  So emergency cooling could be provided by embedding water pipes within the concrete biological shield.  These could dump heat into an ice covered pond on the Martian surface.

Last edited by Calliban (2022-09-27 12:25:08)


"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."

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