Nuclear power is safe

kbd512 · 2021-09-29 23:09:01

For people who have to live a minimum of 2 meters underground for adequate long-term radiation shielding from GCR, the radiation release from a nuclear warhead detonated on the surface would have no discernible health effects. Any reactor that's buried a mere 20m from an occupied structure is already shielded as well as or better than any reactor used here on Earth. Referring back to the group of people who receive the smallest radiation dose here on Earth, those people are sailors serving aboard nuclear powered submarines. In short, the incessant hysteria over radiation exposure, or complete lack thereof for almost all reactors operated here on Earth, is wildly overblown.

Here on Earth, all the money behind Google can't power one silly data center 24/7 with solar panels and batteries, in one of the sunniest states in the entire country, but we're going to drop off a million people 50% further from the Sun, and take care of their every energy need- starting from absolutely nothing to the most technologically advanced civilization humans have ever created, cradle-to-grave, using solar panels and batteries? Well, that's just pure fantasy land thinking.

Calliban · 2021-09-30 09:33:40

I have been away from this board for a while. Work commitments are increasing. A few thoughts come to mind:

1) Building a nuclear reactor underground does provide a lot of passive safety. In the event of a meltdown, there is nowhere for the fission products to go. On Earth, it is not so easy, because building a seismicaly qualified underground bunker of sufficient size is costly. It is something that has been considered periodically and may be done in the future. For compact, sodium cooled reactors, it is an appealing option. On Mars, it would work even better, because there is far less seismic activity. Additionally, there is little or no ground water, at least so far as we know.

2) The radiological risk associated with launching nuclear fuel from Earth depends upon the isotopic composition of the fuel and how it is packaged. Low enriched uranium is low activity and there is essentially no radiological risk if this returns to Earth in some kind of launch accident. Reactor grade plutonium is 1 million times more toxic than uranium. We don't necessarily need to launch a lot of this material, because a single fast reactor on Mars, equipped with a pyroprocessing machine, could breed sufficient new fuel to start a new reactor in as little as five years of operation. There are solutions for packaging nuclear materials to survive launch accidents. But shipping enriched uranium instead of plutonium, avoids the radiological hazard altogether.

3) Nuclear reactor technology has gradually grown to be more expensive here on Earth. Back in the early 1970s, light water reactors were built quickly and cheaply. Since then, build times have increased substantially and so have costs. A new light water nuclear reactor built today, costs roughly 10 times what an equivalent unit did in the 1965-80 period. A large part of the reason behind this is growing complexity and the now extreme quality control that goes into nuclear components. This is above and beyond that applied to any other large scale industry. There are certainly critics that doubt that this evolution has resulted in improvements commensurate with cost. Part of the solution can be found in designs that achieve safety through passive means. On Mars, we have the opportunity to leave the cumbersome bureaucracy of Earth behind and take a pragmatic view that achieves safety without runaway costs and counterproductive complexity.

4) Practical fusion power is not a promising approach here on Earth. There are two factors that have made its development far more difficult than was neccesary:

(a) The focus on magnetic confinement. The limited plasma pressure that can be contained by achievable magnetic fields will curse magnetic confinement fusion to low power density - orders of magnitude lower than nuclear fission reactors. This in itself will make breakeven difficult to achieve. It makes an economically viable fusion reactor almost impossible. But there is huge institutional inertia against investing in other approaches. Whilst inertial confinement fusion has problems of its own, there is at least the potential for an economic powerplant at the end of it, due to the several orders of magnitude improvement in plasma density in an imploding fuel pellet.

(b) The rigid separation of fission and fusion research has resulted in a failure to pursue some of the most promising options for nuclear fusion. I have discussed on this board before the possibility of using tiny amounts of fissile materials as a trigger for igniting inertial confinement fusion. It makes the whole process enormously easier, because ion beams or lasers are then deployed to compress the fuel pellet to 10% of its original diameter, without the need for igniting the pellet. The entire driver assembly can be far more compact. Fusion events produce an abundance of very fast neutrons. It is actually difficult in to design magnetic confinement machines that can extract energy from these neutrons, because liners become brittle and radioactive. However, those very fast neutrons (12MeV) are very useful for driving nuclear fission. In a normal nuclear reactor, we must first convert 238U or 232Th into plutonium or 233U, which then fission when struck by a neutron. However, very fast neutrons will cause 238U or 232Th to fission directly. Neutrons of this energy range >1MeV are produced in fission reactors, but are never a large fraction of total flux. But they are produced by fusion in abundance, in fact most of the energy from fusion is released in this way. Neutrons with 12MeV energy will reliably fast-fission 238U or 232Th without the need to breed plutonium or 233U first. That is enormously beneficial. It means that every 12MeV of energy released by fusion, catalyses the release of another 200MeV by a fission event in the blankets. As fission proceeds and 233U and 239Pu builds up in the blankets, each fusion event in a hybrid reactor will drive several fission events. The reactor can be loaded with thorium metal, which is not heavily radioactive and can be handled and machined without radiation precautions.

My proposal is that we begin Martian settlement using fast reactors, with enriched uranium fuel imported from Earth. However, Mars is known to posses substantial inventory of thorium. Relatively early in the colonisation timescale, Martian colonists may find it beneficial to build fusion-fission hybrid reactors. These would consist of an inertial confinement fusion core surrounded by fissionable (not fissile) thorium metal blankets. Within the core, pellets of lithium deuteride containing a pin head of 233U at their centre, are compressed using ion beams until the 233U goes critical. The fission products spiral into the surrounding lithium deuteride heating it to temperatures of several hundred million K. This sends a fusion detonation wave through the pellet. Neutrons streaming out of the pellet explosion then cause fast-fission in the thorium blankets. The high power density assembly sits in a tank of liquid sodium, which transfers energy to compact S-CO2 generation loops.

Such a 3-stage hybrid reactor could be very compact. I wonder about the possibility on building it on Earth and shipping it to Mars. Most of the energy released comes from nuclear fission. But fusion provides the very fast neutrons needed to fast-fission the thorium in the blanket. And fission can drive the fusion - essentially the pellets are micro hydrogen bombs, using ion beams to drive compression instead of chemical explosives and fission in the pellet providing the heating energy needed to trigger fusion. The concept doesn't really need any reprocessing, as you load it with stainless steel clad thorium metal. This would be discharged when 10-20% of the original thorium has undergone fission. The spent fuel can either be buried as waste, or electrorefined to provide fuel for downstream fission reactors. A single fusion-fission hybrid could breed sufficient fissile material to fuel several standard light water reactors. Although I suspect that sodium cooled fast reactors would be better options on Mars.

The speed with which the energy crisis is unfolding, means that we now need something like this on Earth, as soon as possible. Whilst I was aware of fossil fuel supply constraints and declining surplus energy, the speed with which supply constraints have emerged has shocked me. All of a sudden, inflation is surging and entire industries are shutting down.
Nuclear power has gone from being something that was beneficial to have, to something that we now have to build up quickly, or we will die. I think the public at large are finally starting to cotton on to this. So long as the world wasn't collapsing around them, they were prepared to indulge idealistic fantasies from the renewable energy crowd. Now the consequences of FF depletion and the inadequacy of large scale renewable energy is in people's faces. As bad as the next 10 years are going to be, they do provide the opportunity for positive change.

Last edited by Calliban (2021-09-30 10:48:38)

kbd512 · 2021-09-30 09:43:10

Calliban,

If only there was a "like button" for your last post.

Calliban · 2021-09-30 11:51:45

kbd512 wrote:

For people who have to live a minimum of 2 meters underground for adequate long-term radiation shielding from GCR, the radiation release from a nuclear warhead detonated on the surface would have no discernible health effects. Any reactor that's buried a mere 20m from an occupied structure is already shielded as well as or better than any reactor used here on Earth. Referring back to the group of people who receive the smallest radiation dose here on Earth, those people are sailors serving aboard nuclear powered submarines. In short, the incessant hysteria over radiation exposure, or complete lack thereof for almost all reactors operated here on Earth, is wildly overblown.
Here on Earth, all the money behind Google can't power one silly data center 24/7 with solar panels and batteries, in one of the sunniest states in the entire country, but we're going to drop off a million people 50% further from the Sun, and take care of their every energy need- starting from absolutely nothing to the most technologically advanced civilization humans have ever created, cradle-to-grave, using solar panels and batteries? Well, that's just pure fantasy land thinking.

Agreed. This puts the insanity of the situation into context. Cosmic radiation dose rates on the surface of Mars, are about as heavy as the gamma dose rates in the most heavily contaminated areas of the Fukushima evacuation zone in the first months after the accident. If we are going to this place voluntarily and moving around on the surface, we are already living with a hazard that is as bad as living on land next door to a nuclear meltdown. I calculated a while back, that the effects on human life expectancy of living in that sort of background radiation, is about the same as air pollution here on Earth. It just isn't the scary thing that a lot of people imagine it to be. If we applied the same standards to air pollution as we do to radiation, we would have to permanently evacuate all of our cities.

And people will likely live underground anyway, to reduce dose rates and protect themselves from the Siberian temperatures of the Martian night. They will build their reactors underground as well. Nuclear radiation just isn't going to be a dominant threat on Mars. But the threat of running out of air, water, food and heat, is like a Sword of Damaclese hanging over everyone's head. And everybody's quality of life will be an inverse function of the cost of energy. Cheap, reliable energy is very important on Earth. On Mars, life will depend on it. It's one thing being poor and malnourished on a planet where air, water and survivable temperatures are free. Imagine being poor on a planet where you have to buy the air you breath and where clean water has the same energy cost as concrete. It is a sign of technical illiteracy that anyone would suggest sending people to live on Mars and try and build an expanding society there using solar panels as the primary energy source.

Last edited by Calliban (2021-09-30 11:54:34)

tahanson43206 · 2021-10-01 22:48:24

SpaceNukes’ David Poston to Discuss Mars Reactor Technology at Mars Society Convention
The Mars Society is pleased to announce that Dr. David Poston, Co-Founder of Space Nuclear Power Corporation (SpaceNukes), will discuss the company’s plans to evolve its reactor technology to 5-Mwe Mars surface power systems during the 24th Annual International Mars Society Convention, scheduled for October 14-17, 2021.
SpaceNukes has developed a simple, step-wise evolutionary approach to high-power systems that is rooted in KRUSTY – the 1-kWe Kilo-power system prototype that was successfully designed and developed in 2018, and was the first successful nuclear-powered test of a space reactor in the U.S. in over 50 years.
Dr. Poston has spent his career at GE Nuclear Energy and the Los Alamos National Laboratory leading the design of small special purpose reactors for government and commercial applications. Numerous failed programs during his career has led Dr. Poston to change his focus from trying to design the best reactor on paper to the best reactor that can realistically be developed and deployed.
He received a B.S. degree in Mechanical Engineering from the University of Michigan, an M.S. degree in Mechanical Engineering from Stanford University, an M.S. degree in Nuclear Engineering from the University of California Berkeley, and a Ph.D. in Nuclear Engineering from the University of Michigan.
This year’s virtual Mars Society convention will be free of charge (although donations are welcomed). For complete details, including online registration, a list of confirmed speakers, and sponsorship opportunities, please click here. Regular updates will be posted in the coming weeks on the Mars Society web site and its social media platforms.
The Mars Society
11111 West 8th Avenue, unit A
Lakewood, CO 80215 U.S.A.
www.marssociety.org
https://www.facebook.com/TheMarsSociety
@TheMarsSociety
Copyright (c) 2021 The Mars Society
All rights reserved.

(th)

SpaceNut · 2021-10-02 20:38:25

On Friday, Sept. 10, the U.S. Department of Energy granted the state an emergency order to allow natural gas power plants to operate without pollution restrictions so that California can meet its energy obligations. The order is in effect until Nov. 9.

At the same time, the Diablo Canyon nuclear power plant, owned by Pacific Gas and Electric and located near Avila Beach in San Luis Obispo County, is in the middle of a decade-long decommissioning process that will take the state's last nuclear power plant offline. The regulatory licenses for reactor Unit 1 and Unit 2, which commenced operation in 1984 and 1985 will expire in November 2024 and August 2025, respectively.
Diablo Canyon is the state's only operating nuclear power plant; three others are in various stages of being decommissioned. The plant provides about 9% of California's power, according to the California Energy Commission, compared with 37% from natural gas, 33% from renewables, 13.5% from hydropower, and 3% from coal.
California is a strong advocate of clean energy. In 2018, the state passed a law requiring the state to operate with 100% zero-carbon electricity by 2045.
The picture is confusing: California is closing its last operating nuclear power plant, which is a source of clean power, as it faces an energy emergency and a mandate to eliminate carbon emissions.

tahanson43206 · 2021-10-03 08:34:02

For SpaceNut re #356

Thank you for finding this link, and for posting the excerpt! The closing paragraph is telling.

The forces of fear and ignorance are strong in the US. I read a brief report yesterday that the contagion of mental instability that is infesting the US has spread to Europe.

It is almost as though a culture can experience a kind of dementia.

***
My relative who lives in Phoenix is very analytical, and seems determined to convince himself of the validity of the proposal that atomic power would be better used to make fresh water than electricity for the spot market. I applaud his insistence upon having all his facts in hand and well understood before he contacts anyone in government or other position of authority, but I worry that delay may reduce chances of success.

However, it turns out he is almost the ideal person to consider the question for the State of Arizona, because he has been an advocate for water for farmers for many years, and is more informed about the needs of his neighbors than I am about mine (for sure).

His latest round of conversation on this subject led to consideration of a cooperative arrangement with Mexico.

My thought initially had been to keep involvement with Mexico to a minimum. My proposal was to trade a supply of sea water from the Gulf of California for 10% of the supply returned to Mexico as fresh water.

However, my relative led me to discover that Mexico already has two nuclear reactors, and they do not have the problem of opposition to nuclear power that exists in the US. What Mexico **does** have is a subculture of contempt for law fed by income from the drug trade with the US.

At the current stage of the conversation, it appears my relative is leaning toward the idea of building a brand new Palo Verde scale plant near the Mexican border, so that the existing Palo Verde system can continue it's important role of providing almost all the clean power that Arizona enjoys at this point.

***
Returning to the curious behavior of Californians .... If they persist in closing their last remaining nuclear power plants, then they will become candidate customers for both electrical power and fresh water, if Arizona chooses to harness atomic power on a grand scale.

Assuming a cooperative arrangement with Mexico, and specifically the State of Sonora, is possible, then that region has the potential to become a power center, in both the literal and figurative sense.

A complication is that the land where such a plant might be build is managed by Native Americans.

It is possible that the idea of providing fresh water to neighbors might appeal to them, in return for control over and management of the plant.

(th)

Calliban · 2021-10-14 08:59:30

An interesting reactor system that was explored at the very beginning of the nuclear age: the molten plutonium reactor.
https://atomic-skies.blogspot.com/2013/ … art-1.html

The LAMPRE-2 reactor consisted of a tantalum crucible, holding liquid, metallic plutonium. Essentially, pure fissile material, with a neutron spectrum about as hard as physically achievable. Sodium is bubbled through the liquid Pu and carries away the heat as it separates by density.

The Cons: Liquid plutonium is highly corrosive. Finding a refractory metal that could contain it without corroding excessively, was a challenge. Tantalum was chosen, though tungsten and molybdenum have potential as well. A reactor running on separated weapons grade plutonium, is obviously a proliferation nightmare. About the worst system imaginable from a proliferation perspective.

The Pros: Enormous core power density. The heat transfer rate between the liquid sodium coolant and liquid plutonium metal, is 1-2 orders of magnitude greater than HTR out of solid fuel and into liquid sodium coolant. This would allow for very compact nuclear systems. A reactor core capable of generating 2GW of heat and 1GWe, enough for a city of 1-2 million people, would have the volume of a waste paper bin. Coupled to an S-CO2 generator set, whole system power density would be greater than any power generation technology developed by human beings to date. A 1GWe unit, would be the size of a suburban house. Other advantages are continuous removal of fission products, without need for shut down; high primary circuit temperatures (suitable for thermochemical hydrogen and synthetic fuel production); high power power output per kg of fissile material resident to the core. But more significant than any of that, the very hard neutron spectrum and absence of other absorbers, would allow very high breeding ratio in surrounding uranium metal blankets.

The pros probably don't outweigh the cons here on Earth. But on Mars, a technology like this could be game changing for rapidly growing population, that needs a lot of cheap energy to grow and prosper in such a cold and difficult environment. The problems of proliferation would appear to be less severe on Mars. And with no ground water and little seismic activity, such reactors can be built in compact cavities underground. It the event of an accident, radioactivity is sequestered in a geologically stable underground storage. There is no biosphere to contaminate. So safety strategy can be based upon the two simple and cheap precidents, of using rock to store excess decay heat and a robust underground storage cavern that can be sealed if things go too wrong. Simple, very compact systems, that are easy and quick to build and operate constantly for decades without shutdown. Exactly what we need on Mars.

Last edited by Calliban (2021-10-14 09:05:36)

tahanson43206 · 2021-10-14 09:37:03

For Calliban re #358

Impressive find!

Would you be willing to develop this idea a bit further?

If there's one thing you've impressed upon me over the time you've been contributing to the forum, it is the importance of heat management.

If the plant you've described is in a cavity under ground, and there is little or no water on Mars (compared to the Earth for example) how would the energy flow take place so that (about) 50% is captured for useful purposes.

A hint along those lines is sinking heat into materials for a variety of manufacturing processes.

Is it possible - practical to set up a flow of material to soak up the heat over an extended period?

Can the heat flux be controlled, adjusted ?

This would be an all-robotic (or teleoperation) "work" environment.

Is there any risk of radioactive materials escaping with the flows of materials to receive thermal treatment?

One thing seems certain ... the Mars population would be in an excellent position to develop nuclear devices for defense purposes.

Human nature being what it is, failing to plan for defense seems unwise.

(th)

tahanson43206 · 2021-10-14 11:37:11

For Calliban ...

There seems to be some evidence that nuclear fission is still happening inside the Earth.

I came to this line of thinking after your recent post about a reactor in a cavity on Mars had time to settle.

The center of the Earth (or Mars for that matter) would seem to be a suitable place for a powerful nuclear fission reactor.

Delivery of thermal energy from the Center of the Earth is presently quite random in nature.

Humans do NOT have to continue putting up with the random variations of volcanic activity, or weather either.

If you were serious about meeting energy needs of Europe (or any other continent where the need is greater than the supply) I would expect to see you leading the way toward efficient and cost effective harnessing of thermal flows from the planetary core reactor.

There are some small scale experiments with geothermal power around the world.

This is the NewMars forum. You have ** permission ** from the Gods of NewMars Forum (???) to think on a larger scale, and with more self-confidence.

Your deep and broad distrust of human beings, and humanity taken as a class, may be inhibiting your creativity.

I'm here to (at least try to) encourage you to address the problems of the age on the scale required.

(th)

Calliban · 2021-10-15 04:07:56

tahanson43206 wrote:

For Calliban re #358
Impressive find!
Would you be willing to develop this idea a bit further?
If there's one thing you've impressed upon me over the time you've been contributing to the forum, it is the importance of heat management.
If the plant you've described is in a cavity under ground, and there is little or no water on Mars (compared to the Earth for example) how would the energy flow take place so that (about) 50% is captured for useful purposes.
A hint along those lines is sinking heat into materials for a variety of manufacturing processes.
Is it possible - practical to set up a flow of material to soak up the heat over an extended period?
Can the heat flux be controlled, adjusted ?
This would be an all-robotic (or teleoperation) "work" environment.
Is there any risk of radioactive materials escaping with the flows of materials to receive thermal treatment?
One thing seems certain ... the Mars population would be in an excellent position to develop nuclear devices for defense purposes.
Human nature being what it is, failing to plan for defense seems unwise.
(th)

There is no shortage of uses for direct heat on Mars. Agriculture will be carried out in poly tunnels. The problem is that Martian surface temperatures are beneath freezing most of the time. So we will need to run heating pipes through those poly tunnels. Surface habitats will need heating as well.

We also need heat for water extraction. Brick making will require heat between 30-200°C for drying and 800-1300°C for firing. Simple mud bricks could be made by drying at 30°C. Concrete relies on heat for production of lime and cement will need to be heated on Mars while it sets. Steel production will use CO or H2 as a reducing agent. But high temperature process heat would be valuable in bringing the iron ore up to high temperatures before chemical reduction.

In terms of how to transfer the heat: The S-CO2 generator sets will use CO2-water heat exchangers to generate the pressure drop across the turbines. This would generate a lot of warm water at a temperature of around 30°C. Perfect for agricultural and habitat heat loads. These uses also provide a means of dumping the heat that avoids the need for an engineered radiator or boreholes. There is no direct contact with radioactivity, because the S-CO2 system sits between the water and radioactive sodium. Likewise, high temperature process heat would probably require pumping the radioactive sodium through a heat exchanger, which would transfer heat to a secondary sodium circuit. For some uses, such as brick firing, we could avoid the need to a secondary heat exchanger, by pushing the bricks through a long tube, with primary, radioactive sodium heating it. But in most cases, a heat exchanger is desirable.

If we were to build nuclear power plants close to the poles on Mars, then power production can be accomplished by loading solid dry ice into boilers, with CO2 gas passing through gas turbines into the atmosphere. This would give excellent pressure ratio and high efficiency from very compact machines. But it does entail a lot of mining.

Decay heat strategy for a liquid Pu-sodium reactor would rely on natural circulation of sodium through steel pipes running through bodies of rock. This provides an entirely passive solution for decay heat, without need to operate pumps or standby generators. Just open the valves. The plant would have trip settings on primary sodium temperature. If for whatever reason the downstream heat sink is lost, operators would have a certain grace time given by internal heat capacity to reduce plant power levels. If they don't, automatic trip setting would drop control rods by gravity. Solenoids or hydraulic pressure holding valves closed would be released and the plant would cool itself by natural circulation through the rock. This ensures that it stays safe even if no operator if present to shut it down.

Shielding would be provided by the rock itself. Without ground water, we do not need to be worried about activation products in irradiated rock that is deep underground, actually going anywhere. So the reactor vessel is simply sunk deep enough into a pit of rock to ensure that neutron and gamma levels are sufficiently reduced at the operating floor.

Waste removal is carried out by removing portions of the liquid sodium, which will carry fission products and replacing it with fresh sodium. The radioactive sodium will then be placed in steel casks. After initial cooling, the sodium can be reduced by controlled oxidation. Volatile fission products will be removed and the remaining sodium oxide and fissium oxides can be used in radiothermal power sources. Kbd512 discussed a plan a while back in which strontium-90 provided a power source for interplanetary fusion based propulsion. Final waste disposal will be carried out by encasing waste in steel casks and dropping into boreholes deep underground.

Decommissioning strategy will involve removing the liquid plutonium into tantalum lined, steel casks by pressure siphoning. The liquid plutonium is transferred to a new reactor core. After this is done, the old reactor cavity is sealed for 300 years to allow fission products and irradiation products to decay, prior to dismantling. Decommissioning will recycle most materials, but highly radioactive materials such the reactor vessel and primary pipework and heat exchangers, will be disposed of in deep boreholes in steel casks.

Last edited by Calliban (2021-10-15 04:53:31)

tahanson43206 · 2021-10-15 06:27:18

For Calliban re follow up to question about heat flow ...

SearchTerm:Sodium Plutonium reactor high power
SearchTerm:Plutonium liquid bubbling boiling nuclear reactor

The image of a tiny power source producing ** that ** much energy in a controlled manner is inspiring!

One followup would appear to be in order ...

I suspect you may have intentionally left a teaser to see if your readers (of whom of course I am only one) would pick up on the poor conductivity of stone.

In posts long ago and far away in the NewMars archive, you have pointed out that stone is a notoriously poor conductor of thermal energy.

For that reason, I am curious about your apparent assurance that excess heat not consumed by working fluids in a reactor facility far underground on Mars would flow into the mantle at a useful rate.

For SpaceNut ... would you be willing to add a post to this series, to show links to articles on thermal conductivity of various materials?

For Calliban .... SpaceNut's vision of a regolith harvesting system to make fuel for a Starship would ** really ** benefit from a high power reactor.

The boiling Plutonium reactor may be a bit much for SpaceNut's application, but I'm wondering if you have a design in mind for a high power reactor that can be delivered by a spacecraft (such as a Starship but not limited to Starship) and capable of operating SpaceNut's on site factory?

The reactor needs to bake the regolith to release water and any other useful gases that might be present.

It needs to provide power for equipment to collect the regolith, to move it through processing steps and on to final disposition.

It needs to provide power for equipment to chill Oxygen for long term storage of up to two Earth years.

It needs to provide power to collect CO2 and split it for the Oxygen store and also to make methane.

It needs to provide power to make methane.

It needs to be able to provide power to split water collected from the regolith harvest.

The system needs to be sized to deliver 2400 tons of propellant in one Earth year.

The boiling Plutonium reactor could clearly achieve all those goals, but I think it is a bit too ambitious for most Earth citizens to seriously consider.

(th)

Calliban · 2021-10-15 12:59:12

tahanson43206 wrote:

For Calliban re follow up to question about heat flow ...
SearchTerm:Sodium Plutonium reactor high power
SearchTerm:Plutonium liquid bubbling boiling nuclear reactor
The image of a tiny power source producing ** that ** much energy in a controlled manner is inspiring!
One followup would appear to be in order ...
I suspect you may have intentionally left a teaser to see if your readers (of whom of course I am only one) would pick up on the poor conductivity of stone.
In posts long ago and far away in the NewMars archive, you have pointed out that stone is a notoriously poor conductor of thermal energy.
For that reason, I am curious about your apparent assurance that excess heat not consumed by working fluids in a reactor facility far underground on Mars would flow into the mantle at a useful rate.
For SpaceNut ... would you be willing to add a post to this series, to show links to articles on thermal conductivity of various materials?
For Calliban .... SpaceNut's vision of a regolith harvesting system to make fuel for a Starship would ** really ** benefit from a high power reactor.
The boiling Plutonium reactor may be a bit much for SpaceNut's application, but I'm wondering if you have a design in mind for a high power reactor that can be delivered by a spacecraft (such as a Starship but not limited to Starship) and capable of operating SpaceNut's on site factory?
The reactor needs to bake the regolith to release water and any other useful gases that might be present.
It needs to provide power for equipment to collect the regolith, to move it through processing steps and on to final disposition.
It needs to provide power for equipment to chill Oxygen for long term storage of up to two Earth years.
It needs to provide power to collect CO2 and split it for the Oxygen store and also to make methane.
It needs to provide power to make methane.
It needs to be able to provide power to split water collected from the regolith harvest.
The system needs to be sized to deliver 2400 tons of propellant in one Earth year.
The boiling Plutonium reactor could clearly achieve all those goals, but I think it is a bit too ambitious for most Earth citizens to seriously consider.
(th)

This sounds like a concept that will be needed early in the colonisation effort. The reactor concept that powers it will need to be developed soon, quickly and cheaply. I would suggest an aqueous homogenous reactor. This is a tank of water with uranium sulphate or nitrate salts dissolved in the water. Quick, cheap and easy to build. Not particularly efficient, because operating temperature is no greater than 200°C. But this operation needs a lot of direct heat for regolith baking. An AHR would be ideal for that purpose. It would require enriched uranium salts to be imported from Earth. The reactor is self regulating, because increased temperature results in boiling that increases neutron leakage from the core. So control is easy. Waste heat can be used for regolith baking. The electric power can be used for the other things. Generating efficiency would be about 20%. The concept should be designed to use COTS equipment, like turbine, steam dryer and generator.

Starship stainless steel fuel and oxidizer tanks can be used as reactor vessels for subsequent Mars-built AHRs. Martian thorium salts can be added to the reactor vessel along with uranium salts, to produce converter reactors that will breed their own fuel in addition to a small surplus. The liquid plutonium reactor would be a second generation concept developed using plutonium separated from AHR fuel solutions.

If a rapid nuclear buildup is needed on Earth due to the fossil fuel crisis, AHRs are things we could build quickly.

Last edited by Calliban (2021-10-15 13:31:15)

kbd512 · 2021-10-15 14:07:17

Calliban,

If it's practical to make a 2GWt reactor core the size of a garbage can, per your Post #361, then our military can have practical 5,000t flying nuclear-electric powered aircraft carriers.

Space Force can have real interplanetary transport ships that use fission as input power for fusion-based thrusters. Current fusion experiments achieve gains of 200 or greater (not trying to convert the output to electricity, just thermal output power), so if half of the reactor's power is devoted to propulsion and we "only" achieve a gain of 200, then that equates to about 100GW (500MW of input power * fusion gain of ~200) of jet power from fusing D-T pellets using the scheme that MSNW LLC came up with. The pair of solid rocket boosters used by the Space Shuttle provided about 10GW of jet power, so that's like having 10 pairs of solid rocket boosters attached to the ship.

With that kind of thrust on tap, even a 25,000t ship can move swiftly through the radiation of the Van Allen belts, thrusting for a period of minutes to achieve TMI, cruise / coast the rest of the way to Mars, providing artificial gravity and radiation protection using electromagnets, perform an orbital insertion burn at Mars, and then come back to Earth, all without refueling. Although a ship of this type could achieve a greater than 1 TWR, I wager we'd still keep it in orbit to avoid political issues, sending Starships to and from the transports to refuel it or ferry colonists to the ship.

Calliban · 2021-10-15 15:01:17

kbd512 wrote:

Calliban,
If it's practical to make a 2GWt reactor core the size of a garbage can, per your Post #361, then our military can have practical 5,000t flying nuclear-electric powered aircraft carriers.
Space Force can have real interplanetary transport ships that use fission as input power for fusion-based thrusters. Current fusion experiments achieve gains of 200 or greater (not trying to convert the output to electricity, just thermal output power), so if half of the reactor's power is devoted to propulsion and we "only" achieve a gain of 200, then that equates to about 100GW (500MW of input power * fusion gain of ~200) of jet power from fusing D-T pellets using the scheme that MSNW LLC came up with. The pair of solid rocket boosters used by the Space Shuttle provided about 10GW of jet power, so that's like having 10 pairs of solid rocket boosters attached to the ship.
With that kind of thrust on tap, even a 25,000t ship can move swiftly through the radiation of the Van Allen belts, thrusting for a period of minutes to achieve TMI, cruise / coast the rest of the way to Mars, providing artificial gravity and radiation protection using electromagnets, perform an orbital insertion burn at Mars, and then come back to Earth, all without refueling. Although a ship of this type could achieve a greater than 1 TWR, I wager we'd still keep it in orbit to avoid political issues, sending Starships to and from the transports to refuel it or ferry colonists to the ship.

The core can be as small as a garbage can, because the intricately mixed liquid sodium and plutonium would transfer heat into the sodium with more efficiency than would ever be possible between solid fuel elements and liquid coolant. But the other subsystems and heat exchangers would still be bulky in comparison. However, a sodium cooled liquid plutonium reactor attached to an S-CO2 power generation system would be far more power-dense than any other reactor ever built. That should make it a very affordable reactor system.

Whether it will be light enough to actually fly with the shielding solution in place is debatable. But it is noteworthy that the aircraft reactor experiment used a molten salt reactor to transfer heat to air turbines. Sodium allows for an even more compact core arrangement and shielding solution, because of its superior heat transfer capability compared to molten salt. It also has better compatibility with most metals. Shielding mass per unit power generally decreases as reactor size (and power) increases. So at a hunch, a flying aircraft carrier would indeed be possible. Nuclear powered flying ships could in fact replace all aircraft. Crossing the Atlantic on a flying cruise ship would be a lot more comfortable than a 747.

A reusable launch vehicle

Last edited by Calliban (2021-10-15 15:18:48)

kbd512 · 2021-10-15 15:20:49

Calliban,

I have it on good authority that if we paint it green and use lots of meaningless buzzwords to dazzle the mathematically-illiterate with BS, then we can call it "green energy". Maybe we can attach a wind turbine to it while we're at it, throw in a few batteries (in pods, obviously, so that when they catch fire they can be jettisoned over enemy ships), slap some solar panels on it for good measure, and call it a day. It's paying homage to the group-think religion while accomplishing nothing particularly useful that counts.

Edit:

If people have such a big problem with kerosene burners, then I guess they'll have to get comfortable with the concept of neutron burners, because that's the only way anything electric, carrying more than one person on board, will make it across the Atlantic within our lifetimes.

Can you imagine being able to take in a view of the Earth and sky through a window the size of a small office building?

That's what a nuclear powered flying ship would enable.

That sure beats being stuck in coach.

Last edited by kbd512 (2021-10-15 15:25:51)

Calliban · 2021-10-15 17:25:13

kbd512 wrote:

Calliban,
I have it on good authority that if we paint it green and use lots of meaningless buzzwords to dazzle the mathematically-illiterate with BS, then we can call it "green energy". Maybe we can attach a wind turbine to it while we're at it, throw in a few batteries (in pods, obviously, so that when they catch fire they can be jettisoned over enemy ships), slap some solar panels on it for good measure, and call it a day. It's paying homage to the group-think religion while accomplishing nothing particularly useful that counts.
Edit:
If people have such a big problem with kerosene burners, then I guess they'll have to get comfortable with the concept of neutron burners, because that's the only way anything electric, carrying more than one person on board, will make it across the Atlantic within our lifetimes.
Can you imagine being able to take in a view of the Earth and sky through a window the size of a small office building?
That's what a nuclear powered flying ship would enable.
That sure beats being stuck in coach.

It certainly does beat being stuck on a coach :-)

The problem with a reactor system running on pure liquid plutonium metal, is that any country that owns it has material that can easily be used to make bombs. The ship could be hijacked or could crash in a foreign country, effectively handing bomb material to undesirable people. Whilst the dangers of radioactivity are generally overblown, the threat presented by nuclear weapons is very real. On Mars, I don't think it is such an issue on Mars. We could build mobile bases, that could fly to different destinations on the planet. Reusable launch vehicles with launch capacity in the thousands of tonne range, using water as propellant. On a more mundane note, a liquid Pu reactor would be perfect for powering a ground vehicle, as the core and shielding arrangement would be very compact.

On Earth, liquid Pu reactors could produce very compact powerplants with high breeding ratio. A definite option

kbd512 · 2021-10-15 19:38:22

Calliban,

Every nuclear reactor on the planet contains Plutonium and lots of it. After you irradiate the living hell out of the Pu239 by consuming it in a high-burnup fission process, how do you imagine that bombs would be made from it? There's a wild difference between carefully transmuting some U238 in a breeder reactor for one month versus running the Pu239 product as a fuel in an extremely high output reactor. You can't make a bomb out of the fuel because it'll fry everyone and everything in the vicinity for the next few centuries. That's why Plutonium reactor fuel will never become a bomb in practice after it's been thoroughly irradiated during fissioning. Hollyweird movies and baseless anti-humanist arguments aside, you and I both know that won't happen, because it can't happen in any practical sense.

Nobody makes bombs out of Thorium for the same reason. Once the Th232 has been transmuted into U233, it's well nigh unto impossible to make a decent weapon with it, and everybody who has tried to do so has swiftly given up on that process and reverted back to using Uranium or Plutonium. After sufficient contamination is generated via fission, attempting to make weapons out of either U233 or Pu239 is an utter waste of time. You either have a state-run breeder reactor program or you don't have any usable nuclear weapons, simple as that.

We're not talking about handing out Pu239 to the general public like candy. We're talking about taking small quantities of the stuff, running it as fuel in reactors that will render it useless for making bombs in mere days, and there's no such thing as "rolling back the clock" after that process has begun. It's irreversible. It won't become stable enough to make a bomb for at least a few thousand years. By that time, if we haven't already killed ourselves with designer viruses or ill-advised AI experiments, then humanity will become AI-enabled machines using warp drive powered ships to explore other galaxies.

China wiped out millions of people without using a nuclear anything, yet there were no real consequences to them for doing that. Nuclear weapons are the old WMDs. Any significant usage of those devices essentially leaves the entire planet uninhabitable, which is not particularly useful to anyone. Viruses and AI are the new WMDs, and have the ability to surgically take out your enemies without ending humanity.

Calliban · 2021-10-16 06:59:18

Kbd512, Agreed. The reprocessing strategy for the LAMPRE-2 reactor concept, does support what you have written. As the molten Pu and Na separate by density (Pu is 25x denser than Na), the two-phase boiling Na carries most fission products with it. So portions of the Na are bled off during refuelling cycles and replaced for with fresh Na and small amounts of Pu metal. The dirty Na is disposed off as waste, probably through direct mixture with molten glass. The Pu is only extracted at end of reactor life and will be too contaminated with fission products to handle. Fresh Pu for loading into the reactor will be produced from 238U breeder blankets surrounding the core. These will need to be chemically reprocessed to extract Pu. Quite an expensive operation, requiring a lot of Chemical Engineering expertise. Not something that any Tom, Dick or Muhammed can cobble together in their back yard.

Fresh Pu will be in the form of pellets coated with stainless steel. They are safe for manual handling. Just don't put too many in the same place at the same time. A 2GWth reactor would burn about 2kg of Pu each day. That is about 2 golf balls of Pu. To keep reactivity surges to a minimum, it would be better to feed in small pellets almost continuously, say a100 gram pellet every hour or so. Fission products will have much greater volume. At least a couple of litres per day. These should be extracted by removing say 20 litres of sodium per day, replacing it and storing the dirty sodium in steel casks within a liquid lead cooling pool, until DH levels are low enough to allow the Na to be encased in glass.

The next challenge is to design a concept that generates power or thrust without dilluting the enormous power density benefits of the core. Power density this high is comparable to a contained explosion! As soon as heat exchangers are introduced into this concept, whole system power density declines dramatically. One idea I had would be to allow the primary sodium to get hot enough to boil (>880°C); pass the two-phase boiling sodium through a MHD generator and then condense it within a heat exchanger that has liquid lead on the other side. That generates the pressure drop needed to produce power in a MHD generator. The liquid lead is then circulated through a high temperature radiator. The really good thing about this is zero moving parts in the whole system, since the generator has no moving parts and the lead pump will be MHD as well. The yielded electric power can be used for the fusion drive in a spacecraft or aircraft or will be sent onto grid for a powerplant. Another alternative would be to pass the boiling sodium through heat exchangers in S-CO2 power generation loops. Two loops provide redundant heat removal capability. For an Earth-orbit or Mars-orbit launch vehicle; an intermediate lead heat exchanger would interface with primary sodium and lead would transfer heat into ramjet engines that use air and water as propellant. Water would be used as propellant at takeoff, then air, then water again above a certain altitude.

Last edited by Calliban (2021-10-16 07:45:47)

tahanson43206 · 2021-10-16 09:09:17

For Calliban re #369

Kbd512, Agreed. The reprocessing strategy for the LAMPRE-2 reactor concept, does support what you have written. As the molten Pu and Na separate by density (Pu is 25x denser than Na), the two-phase boiling Na carries most fission products with it.

The design you've described would appear to work in a gravity field.

Would any adjustments be needed if the reactor is in space?

For example, would it make sense to mount the reactor in a location where artificial gravity is available?

Is it only when reprocessing is needed that gravity is required? Will the boiling Plutonium reactor work well in space?

Will changes in gravity (such as caused by acceleration) have any effect (positive or negative) on performance of the system?

(th)

tahanson43206 · 2021-10-16 10:44:38

For Calliban re link to Wikipedia in another topic ...

The article mentions production of Hydrogen through normal operation of the reactor, due to neutron activity.

https://en.m.wikipedia.org/wiki/Aqueous … us_reactor

Other research Edit
The use of an aqueous homogeneous nuclear fission reactor for the simultaneous hydrogen production by water radiolysis and process heat production was examined at the University of Michigan, in Ann Arbor in 1975. Several small research projects continue this line of inquiry in Europe.
Atomics International designed and built a range of low power (5 to 50,000 watts thermal) nuclear reactors for research, training, and isotope production purposes. One reactor model, the L-54, was purchased and installed by a number of United States universities and foreign research institutions, including Japan.[5]

I was happy to see that the idea has been investigated, but the article does not provide detail on the effectiveness of the technique.

It would seem advantageous (to me at least) to produce Hydrogen directly from the heat plant needed for power for other activities at a propellant manufacturing site on Mars.

(th)

Calliban · 2021-10-16 10:53:20

The system does require a gravity field or artificial gravity, as gravity is needed to separate the Pu and Na by density. It may be possible to build solid fuelled reactors that operate in zero gravity. But fluid fuelled reactors do need gravity because they rely on natural circulation.

Regarding the AHR, catalytic recombination is used to prevent H2 and O2 accumulation. The difficulty in attempting to harvest H2 and O2 from the primary circuit is that fission products will be removed as well.

Last edited by Calliban (2021-10-16 11:03:55)

Calliban · 2021-10-18 05:09:24

One way of improving whole system power density for the Liquid Pu reactor, is to use the secondary heat transfer fluid as part of the shielding. The core would be surrounded by a tank of liquid 208Pb, which would contain the primary to secondary heat exchangers. The dense liquid lead would also serve as a very efficient neutron reflector, reducing neutron leakage from the core.

Critical diameter for a non-reflected sphere of 239Pu is 9.9cm. The halving thickness of lead shielding is about 1cm, for gamma rays, though this value does vary with energy. This indicates that it may be possible to build a small reactor producing up to 1MW of power, with a diameter of as little as 0.5m, shielding included. A cylindrical reactor of these dimensions would weigh about 1 tonne, shielding included.

Such a reactor could power a car sized rover with effectively infinite range. It could also provide power to construction equipment, which would carry tanks of liquid CO2 or water propellant to avoid the need for massive radiators. Such things are unthinkable on Earth. Mars is in many ways a test bed for things that no Earth based authority would dare to try. On a planet where natural background radiation levels are equivalent to the most heavily contaminated areas following the Earth's most severe nuclear accidents, radiation is something that people will learn to live with. On Mars, it won't freak people out in the way it does on Earth, because it be all around them anyway.

Reactors in this size range can be inserted into vehicles and removed as whole units, when reprocessing is required. Lets us assume that a rover on Mars can achieve millage equivalent of 100mpg in the lower gravity. Let us further assume that the core can accumulate 1kg of fission products before shutdown is needed. A single kg of 239Pu will yield 80TJ of energy when it undergoes fission. This would give a nuclear powered rover a range of 80million km, before the core needs replacing. The vehicle could drive continuously at 40kph for 2 million hours (228 years). It would therefore appear that a vehicle equipped with a unit like this would not need to replace or refuel it in any realistic lifetime.

Last edited by Calliban (2021-10-18 05:44:17)

tahanson43206 · 2021-10-18 05:50:24

For Calliban re #373 and entire series on liquid Plutonium reactors ...

Thank you for producing these enlightening posts! They add significant value to the forum collection as a whole, and are morale boosters for those hoping to imagine ways of approaching the Mars settlement problem with any chance of success.

In reading #373, and remembering previous posts along the same line, it occurred to me to wonder how the operator of such a reactor would move from unpacking the crate of parts to monitoring a running reactor.

Specifically, I'm thinking about the molten lead, although ** all ** the parts that need to be liquefied must become liquid without injury to the containment structure, which (presumably) needs to remain solid.

The components will all be manufactured on Earth and delivered in solid form. They will be assembled by telerobots (most likely), operated by humans at a safe distance, which might be Mars Low Orbit, or closer after a base is established.

From that starting point, I'm tossing the vision back to you...

We want to end up with a fully operational piece of field equipment, able to take on tasks like collecting regolith for SpaceNut's propellant plant, or transporting chunks of ice for Louis' fields of solar panels, to make water for Void's lake.

(th)

Calliban · 2021-10-18 07:41:49

I am digressing a little by talking about ground vehicles and letting my imagination run away with me.

For near term applications in which units are shipped from Earth, the Kilopower units are close to completion and it would be most sensible to base applications on these units. They could be operated remotely, or with an operator in a pressurised cabin. For remotely piloted vehicles, shielding mass can presumably be reduced, but in that case, work must stop if a human being is present in the area.

The primary nuclear systems are fully developed. It is just a case of integrating the units into vehicles and other functions. Most of the mass of these units appears to be associated with power conversion equipment. If we are using liquid CO2 as propellant within engines, then radiators and bulky Stirling cycle engines are not needed. Compact gas turbines driving hydraulic pumps and storing energy in hydraulic reservoirs, would be better options. We would surround the reactor units with tanks of liquid lead, which would serve as both shielding and thermal energy stores. The lead tank would contain a heat exchanger, which would boil water or CO2, generating high pressure gas for the engine. The reactor would operate at steady power, charging the thermal energy store. The power generation cycle would charge the hydraulic accumulator. For construction equipment, like diggers, this allows short bursts of power, which greatly exceed the reactor power capacity. The hydraulic accumulator allows for rapid transients, the power generation cycle may be more sluggish.

A small closed loop generator would run a compressor, compressing and liquefying CO2 from ambient air, 24/7. With air temperatures of -50°C, very little pumping power is needed to produce liquid CO2, as this is close to CO2 triple point. The liquefaction device would be carried on board a long-range rover. But for construction equipment, it is more efficient to keep it separate and stationary from the vehicles, refilling L-CO2 tanks from a central reservoir when they run dry.

The engine would exhaust gaseous CO2 at a temperature of at least a few hundred °C. It would be sensible to pass exhaust CO2 through some sort of recuperator. This would reduce required reactor power, extend core life and reduce shielding mass, given that this is a function of reactor power. A 10kWe Kilopower unit has a continuous operating life of 10 years. So with a 50% utilisation rate, it should be good for the entire operating life of any vehicle on Mars.

Last edited by Calliban (2021-10-18 08:08:19)

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