August 07, 2025
Nuclear Reactors fot the Moon
Timothy Birdnow
So NASA has [link=https://www.france24.com/en/americas/20250806-space-race-us-aims-to-beat-out-china-and-russia-with-nuclear-reactor-on-the-moon
There are a number of problems with this idea, and a number of benefits.
The benefits - a nuclear reactor can run nonstop and provide power 24/7 (a dubious concept on the Moon, which has a different time cycle), it does not require long and dangerous surface walks to deploy it, and it is not subject to the dangers of being hit by meteors or blown out by large solar flares. Also, there is no danger of the batteries needed for solar catching fire (which may be a moot point as you could put them in vacuum).
On the other hand Uranium is the heaviest naturally occurring element in nature (Plutonium does exist in minute quantities but it is usually bonded with other elements) and lifting it might seem a bitch - until you realize it only takes a few pounds of uranium to run a nuclear reactor. 6.8 lbs. of Uranium can produce a million kilowatt hours of power. On the contrary, the batteries needed to store power from solar panels are much heavier,and you will need banksand banks of them to store power for the long lunar night (2 weekslong). Also the panels for the power are heavy. You are able to make a nuclear reactor far cheaper in regardsto weight.
However you aren't going to be able to build a water-cooled reactor on the Moon. Water is a precious commodity on that dry desert and so a different cooling system will have to be employed. This will require a Liquid Metal-Cooled Fast Reactor, which uses sodium or lead. Lead is, of course, very heavy. And that presents a problem with the control rods too; you have to send up a lot of lead if that is the plan. You control the reaction in reactors usually with lead rods which can dampen the nuclear reaction.
As this will be too heavy to send to the Moon they will have to use a gas-cooled reactor, probably using carbon dioxide,although you could use helium (and the Moon has a supply of helium III). But you still have to have the graphite control rods.
So it's going to be expensive and difficult to put such a device on the Moon. But it will be just as hard, or harder, to use solar.
There IS a way around this using solar - put your colony at the lunar south pole. There the sun shines all the time and there are shaded areas in craters and valleys that can be kept coold easily. You could put the solar panels in the sunlight and they will run continuously. Of course you still have to lift the batteries there, but you'll need far fewer of them.
Another possibility using solar would be to orbit a string of solar power satellites which use microwave beam (masers) to transmit power to a receiver on the ground-based antenna. That works fine except you will need a number of satellites. Also, orbitting the Moon is different than orbitting the Earth; the Moon is pear shaped and gravity fluctuates. These satellites would need constant monitoring to keep them in proper orbit. Since the Moon rotates so slowly you can't find the geostationary point - there basically is none. Such a system would work fine on Earth (if we didn't ahve an atmosphere) but will be tough on the Moon.
Another matter; muclear waste is a non-issue; you just dump it in a rill and blow the rille over it. And even a meltdown isn't that big an issue as you are on the Moon - you can just vent it out into space. Of course you lose all the power but nobody is going to get cancer or anything else. It's not going into the environment, just venting into space or at worst settling on the lunar regolith. Unless you put the reactor right next door to your settlement you should be o.k.
I think, at least at first, a nuclear reactor is the way to go. Solar will be an important component of a future lunar settlement's energy systems, but not at first. Until solar can be provided using native materials it will be cost-prohibitive. And you don't DARE risk a power failure in so harsh an environment.
But there are also treaties involved, which is why we have never used nuclear in any real capacity in space. The Outer Space Treaty of 1967 was designed to avoid weaponization of space, and that included nuclear reactors because they could hide nuclear bombs. An orbital bomb platform could strike an enemy far more quickly than shooting the ICBM's into sub-orbit and back down. So nukes were banned in space, and the only nuclear power ever used there involved simple radioactive decay in space probes, which could not possibly be used for weapons.
At any rate the U.S. can withdraw from that treaty any time it likes (if it hasn't already, but I couldn't find that in a Google search.)
Still, launching a bumch of uranium into orbit may not sit well with the Russians nor the Chinese. We will probably have to allow them to have inspectors present all the way up until the launch.
And we have to hope the spacecraft doesn't blow up or crash; it will send a bunch of uranium into the atmosphere. A Challenger type disaster would lead to nuclear fallout, at least to a degree. That has also long been a concern with putting nuclear reactors in space.
I would add that it would be logical to use a breeder reactor so as to minimize resupply for the pile. fast breeder reactors use U238, a non-weaponized form of uranium, or thorium 232. There are also two types of breeder reactors - fast and thermal. Fast seems the more logical - they do not need moderation, unlike the thermals. (Moderation is a material like water or graphite that is used to slow down neutrons.)
Breeder reactors are ultimately fusion reactors; the nuclear reaction leads to fusion of heavy elements. Eventually you wind up with plutonium, which in turn fissions back down. Breeder reactors run on geological time scales without needing refueling. We don't use them because we fear the biproduct of plutonium, which could be stolen and weaponized by terrorists. But what will they blow up on the Moon, other than the colony itself?
At any rate it's a good idea and this signals a real desire to go back to the Moon to stay. Mankind needs that as a species; we need a frontier. And we need the resources the Moon can provide.
So NASA has [link=https://www.france24.com/en/americas/20250806-space-race-us-aims-to-beat-out-china-and-russia-with-nuclear-reactor-on-the-moon
There are a number of problems with this idea, and a number of benefits.
The benefits - a nuclear reactor can run nonstop and provide power 24/7 (a dubious concept on the Moon, which has a different time cycle), it does not require long and dangerous surface walks to deploy it, and it is not subject to the dangers of being hit by meteors or blown out by large solar flares. Also, there is no danger of the batteries needed for solar catching fire (which may be a moot point as you could put them in vacuum).
On the other hand Uranium is the heaviest naturally occurring element in nature (Plutonium does exist in minute quantities but it is usually bonded with other elements) and lifting it might seem a bitch - until you realize it only takes a few pounds of uranium to run a nuclear reactor. 6.8 lbs. of Uranium can produce a million kilowatt hours of power. On the contrary, the batteries needed to store power from solar panels are much heavier,and you will need banksand banks of them to store power for the long lunar night (2 weekslong). Also the panels for the power are heavy. You are able to make a nuclear reactor far cheaper in regardsto weight.
However you aren't going to be able to build a water-cooled reactor on the Moon. Water is a precious commodity on that dry desert and so a different cooling system will have to be employed. This will require a Liquid Metal-Cooled Fast Reactor, which uses sodium or lead. Lead is, of course, very heavy. And that presents a problem with the control rods too; you have to send up a lot of lead if that is the plan. You control the reaction in reactors usually with lead rods which can dampen the nuclear reaction.
As this will be too heavy to send to the Moon they will have to use a gas-cooled reactor, probably using carbon dioxide,although you could use helium (and the Moon has a supply of helium III). But you still have to have the graphite control rods.
So it's going to be expensive and difficult to put such a device on the Moon. But it will be just as hard, or harder, to use solar.
There IS a way around this using solar - put your colony at the lunar south pole. There the sun shines all the time and there are shaded areas in craters and valleys that can be kept coold easily. You could put the solar panels in the sunlight and they will run continuously. Of course you still have to lift the batteries there, but you'll need far fewer of them.
Another possibility using solar would be to orbit a string of solar power satellites which use microwave beam (masers) to transmit power to a receiver on the ground-based antenna. That works fine except you will need a number of satellites. Also, orbitting the Moon is different than orbitting the Earth; the Moon is pear shaped and gravity fluctuates. These satellites would need constant monitoring to keep them in proper orbit. Since the Moon rotates so slowly you can't find the geostationary point - there basically is none. Such a system would work fine on Earth (if we didn't ahve an atmosphere) but will be tough on the Moon.
Another matter; muclear waste is a non-issue; you just dump it in a rill and blow the rille over it. And even a meltdown isn't that big an issue as you are on the Moon - you can just vent it out into space. Of course you lose all the power but nobody is going to get cancer or anything else. It's not going into the environment, just venting into space or at worst settling on the lunar regolith. Unless you put the reactor right next door to your settlement you should be o.k.
I think, at least at first, a nuclear reactor is the way to go. Solar will be an important component of a future lunar settlement's energy systems, but not at first. Until solar can be provided using native materials it will be cost-prohibitive. And you don't DARE risk a power failure in so harsh an environment.
But there are also treaties involved, which is why we have never used nuclear in any real capacity in space. The Outer Space Treaty of 1967 was designed to avoid weaponization of space, and that included nuclear reactors because they could hide nuclear bombs. An orbital bomb platform could strike an enemy far more quickly than shooting the ICBM's into sub-orbit and back down. So nukes were banned in space, and the only nuclear power ever used there involved simple radioactive decay in space probes, which could not possibly be used for weapons.
At any rate the U.S. can withdraw from that treaty any time it likes (if it hasn't already, but I couldn't find that in a Google search.)
Still, launching a bumch of uranium into orbit may not sit well with the Russians nor the Chinese. We will probably have to allow them to have inspectors present all the way up until the launch.
And we have to hope the spacecraft doesn't blow up or crash; it will send a bunch of uranium into the atmosphere. A Challenger type disaster would lead to nuclear fallout, at least to a degree. That has also long been a concern with putting nuclear reactors in space.
I would add that it would be logical to use a breeder reactor so as to minimize resupply for the pile. fast breeder reactors use U238, a non-weaponized form of uranium, or thorium 232. There are also two types of breeder reactors - fast and thermal. Fast seems the more logical - they do not need moderation, unlike the thermals. (Moderation is a material like water or graphite that is used to slow down neutrons.)
Breeder reactors are ultimately fusion reactors; the nuclear reaction leads to fusion of heavy elements. Eventually you wind up with plutonium, which in turn fissions back down. Breeder reactors run on geological time scales without needing refueling. We don't use them because we fear the biproduct of plutonium, which could be stolen and weaponized by terrorists. But what will they blow up on the Moon, other than the colony itself?
At any rate it's a good idea and this signals a real desire to go back to the Moon to stay. Mankind needs that as a species; we need a frontier. And we need the resources the Moon can provide.
Posted by: Timothy Birdnow at
07:26 AM
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Booting nuclear waste "out into space" is not as easy as it might seem. You have to get it to escape velocity or it hangs around close to Earth in orbit. Getting it out of the Moon's orbit is pretty easy, but that still leaves it in Earth's orbit. Getting it to Earth's escape velocity is quite a bit harder.
Breeder reactors are not fusion reactors. They still function through fission, but use a different mix of fuel to produce Plutonium as a by product. A self sustaining fusion reaction has not yet been achieved and probably won't be in the forseeable future.
Breeder reactors are not fusion reactors. They still function through fission, but use a different mix of fuel to produce Plutonium as a by product. A self sustaining fusion reaction has not yet been achieved and probably won't be in the forseeable future.
Posted by: Bill H at August 08, 2025 06:34 PM (FRG6e)
2
Bill, you are correct if we are talking about shooting nuclear waste off the Earth but that's not what I'm suggesting. I am suggesting outside, as in on the Moon itself. There are plenty of lava flow tubes to simply put the waste in, or we can dump it in small craters on the farside and bury it by exploding the rim of the crater (the Moon has lots of small craters on farside, quite different than the side we see.
And you are also correct about orbital mechanics. BTW even if we reach Earth escape velocity with this waste (7 miles per second) the stuff will wind up in an eccentric orbit that crosses the Earth's path every so often. You'd have to shoot it WAY out to get it safely away from us. Even then it would be in another orbit and still could wind up troubling us sometime. Better to put it on some lifeless rock (like under the lunar surface) where it stays put and bothers nobody.
BTW There was an interesting t.v. show from the Seventies about that. It had the ridiculous premise that the Moon had been turned into a nuclear waste dump for Earth (what would the cost be to fire all that stuff in orbit?) and then the dump exploded, pushing the whole Moon out of orbit and into INTERSTELLAR space. The base on the Moon had survivors and they passed all sorts of stars and planets and the like, having adventures. Ri-ight...
But the principle of dumping waste on the Moon is sound (not Earth's waste but waste from lunar reactors). The Moon is a dead hunk of rock and there is plenty of space to get rid of it. Doubt anyone would mind, except maybe The Union of Concerned Scientists or Greenpeace.
You're right in that nuclear fission is the primary driver of breeder reactors BUT they are fusion devices as the internal pressure turns lighter nuclear material into heavier - aka fusion. It's not the kind of fusion that occurs in the Sun of course but it is a kind of fusion nonetheless. After fusion turns each element into heavier ones they undergo fission and produce power. That's the reason they run so long - it's like they reconstitute their gasoline and can reuse it.
I agree; we won't have cheap, light element fusion in the forseeable future. Breeder reactors are as close as we can come to them. We aren't good with fusion,but we are pretty savvy with fission, or fission-fusion (as in here).
And you are also correct about orbital mechanics. BTW even if we reach Earth escape velocity with this waste (7 miles per second) the stuff will wind up in an eccentric orbit that crosses the Earth's path every so often. You'd have to shoot it WAY out to get it safely away from us. Even then it would be in another orbit and still could wind up troubling us sometime. Better to put it on some lifeless rock (like under the lunar surface) where it stays put and bothers nobody.
BTW There was an interesting t.v. show from the Seventies about that. It had the ridiculous premise that the Moon had been turned into a nuclear waste dump for Earth (what would the cost be to fire all that stuff in orbit?) and then the dump exploded, pushing the whole Moon out of orbit and into INTERSTELLAR space. The base on the Moon had survivors and they passed all sorts of stars and planets and the like, having adventures. Ri-ight...
But the principle of dumping waste on the Moon is sound (not Earth's waste but waste from lunar reactors). The Moon is a dead hunk of rock and there is plenty of space to get rid of it. Doubt anyone would mind, except maybe The Union of Concerned Scientists or Greenpeace.
You're right in that nuclear fission is the primary driver of breeder reactors BUT they are fusion devices as the internal pressure turns lighter nuclear material into heavier - aka fusion. It's not the kind of fusion that occurs in the Sun of course but it is a kind of fusion nonetheless. After fusion turns each element into heavier ones they undergo fission and produce power. That's the reason they run so long - it's like they reconstitute their gasoline and can reuse it.
I agree; we won't have cheap, light element fusion in the forseeable future. Breeder reactors are as close as we can come to them. We aren't good with fusion,but we are pretty savvy with fission, or fission-fusion (as in here).
Posted by: Timothy Birdnow at August 09, 2025 01:51 PM (kx7n2)
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