Hybrid nuclear fission fusion technologies

tahanson43206 · 2022-03-31 18:31:36

For Calliban re Neutron reflection ... I am offering a post/inquiry about neutron reflection in the Physics topic.

I'm hoping a few forum members, and perhaps a few readers, will be interested to learn how neutrons might be reflected, since they are (by definition) uncharged. I bring this up in the Hybrid topic because ( I am hoping ) neutron reflection might have a role to play in enhancing the movement of neutrons through material to be fused.

In earlier posts, you have reported on several ways of collecting thermal energy from neutrons, and I am sure those will remain important components of any successful energy producing fusion device. However, if neutron reflection is more than just a theoretical possibility, then perhaps it might have a role to play.

(th)

Mars_B4_Moon · 2022-04-04 12:12:03

Space is about to enter its nuclear age: Fission-powered engines would make Spaceships faster and more manoeuvrable

https://www.futurespacetech.com/2022/04 … e.html?m=1

Challenges mentioned in the Nuclear vs. Solar vs. Others thread
https://newmars.com/forums/viewtopic.php?id=7926

Calliban wrote:

The moon is a particularly challenging place for generating power using any technology. Without any atmosphere, waste heat rejection must rely entirely on radiation. Nuclear reactors must operate at high temperatures or must be consigned to operate with extremely bulky radiators. There is a reason why space nuclear reactor designs are either gas or liquid metal cooled. The heat rejection rate of a radiator is proportional to the fourth power of temperature.

Terraformer · 2022-04-05 03:37:52

Nuclear fusion achieved using gas gun (inertial confinement).

Seems promising. Even if break even proves beyond their capability, neutron generators open up a lot of possibilities...

tahanson43206 · 2022-04-05 05:37:09

For Terraformer re #28

Thank you for this find! I was particularly pleased to see that this UK organization pursued the alternative to the sphere, and developed what appears to be a cylinder to carry the fuel, combined with what i gather is a cleverly designed target. Another surprise (to me for sure) was to use Lithium as the energy buffer, so that the chamber in which all this happens is not damaged.

All in all, to the extent I understand the article, i am quite impressed!

It would be ** good ** to see the UK back in the lead on the global stage, at a time when major innovation is greatly needed.

If you have time, please add whatever new information you can find to this topic!

(th)

Calliban · 2022-04-05 06:56:01

Terraformer, this is certainly a novel concept and sounds very promising. A gas gun is definitely cheaper than a particle accelerator.

An impact velocity of 70km/s equates to a kinetic energy of 2.45MJ per gram, or 2.45KJ per mg of fuel. This may be sufficient to compress the fuel to 100+ times the density of water. But to ignite a hot spot they will need either to push impact velocity much higher or include a fissile pin head within the fuel. If the second approach is pursued, then they may already have sufficient compression to achieve fusion. I would be surprised if the idea has not occurred to them. For a power plant, they must achieve a repetition rate somewhere in the region of 1 per second. I don't know how practical that is with a gas gun or if they can make projectiles and targets cheaply enough. But it certainly sounds like an easier technical problem than developing focused heavy ion beams for target compression.

Terraformer · 2022-04-05 07:10:19

Well, that is after all how atomic bombs work -- chemical explosion to compress the fissile material to criticality. And then, in thermonuclear bombs, uses that to ignite fusion, which then produces neutrons to fission a lot more uranium...

Basically, putting this together with your proposal, we have a fusion reactor that generates power in *exactly* the way a hydrogen bomb does But on a far smaller scale.

Have you emailed them about it?

tahanson43206 · 2022-04-05 09:11:18

For Terraformer and Calliban !!!

Go Team!

(th)

Calliban · 2022-04-05 09:57:55

I shall e-mail them and reproduce the e-mail here. The wording needs some precision. I will draft the e-mail this evening.

In the mean time, below is an ENDF file showing the number of neutrons yielded from 238U fission.
https://nuclear-power.com/wp-content/up … uction.png

For a 14.1MeV incident neutron energy, some 4.4 neutrons are yielded by 238U fast fission. If the Fusion occurs within a chamber lined with solid Uranium metal, then each fission event should generate sufficient plutonium for several light water fission reactors of the same power. On Mars, these hybrid reactors would allow us to scale up nuclear capacity at any rate necessary for the needs of colonisation. It effectively frees us from the problems of long doubling time that would limit the rate of building if we relied on sodium cooled fast breeder reactors. It also allows Uranium to be used with 100% efficiency without any waste. A single tonne of Uranium would yield 909,000 MW-days of heat (21.8 billion kWh) at 100% burn up. If fuel costs are $0.01/kWh, then 1 tonne of Uranium would be worth $218m. At that price, we could easily import Uranium from Earth until Martian mining reaches sufficient levels.

How much Uranium would a colony of 1 million need to import per year? If per capita power consumption is 100kW, then 1 million people would consume 36.5 million MW-days per year. Some 40 tonnes of natural or depleted Uranium should be sufficient to power a Martian city of 1 million people for 1 year, if they are equipped with hybrid Fusion fission reactors. This is less than one half of a single starship payload and would have volume of about 2m3. Nuclear fuel is dense!

The super fast neutron stream from the fusion reactor means that there will be no actinide wastes to deal with. The fuel cycle can be simplified by using uranium-plutonium-zirconium alloy as the fuel material at all points in the fuel cycle. Fission products can be removed by melting the metal and mixing it with liquid cadmium. The fission products enter the liquid cadmium leaving clean actinide metal behind. This allows metal fuel to be irradiated in the hybrid and simply recast into LWR fuel. Following burn up in the LWR the spent fuel will be blended with fresh Uranium and returned to the hybrid. In this way, we burn up 100% of actinides and get all of the potential energy out of the original Uranium. The fission products can then be chemically separated into separate streams. The strontium and ceasium are useful for radiothermal power sources. Other isotopes can be deployed according to their individual properties. Noble metal fission products can be used to coat fuel cladding.

Last edited by Calliban (2022-04-05 10:30:12)

Calliban · 2022-04-05 17:05:58

Here is the e-mail. I will post any correspondence that I receive.
******************************************************************

May I offer my congratulations on your recent achievement of neutron production in a high density plasma.

My colleagues and I within the Mars Society have been engaged in theoretical examination of IC Fusion for some time. We are a non-profit organisation dedicated to advancing human exploration of Space. Our principal interest in IC Fusion is the development of spacecraft propulsion systems that combine high exhaust velocity with high thrust. The combination of these attributes in a single propulsion system sets the requirement for very high power - a feature that can only be provided by nuclear pulse propulsion. Additionally, colonisation of Mars and other planetary bodies will require per capita energy consumption much greater than advanced economies on Earth. This is because all human habitable living space must be contained within pressure vessels; air is something that must be manufactured and food must be grown in heated, pressurised greenhouses. Living in this way will be impossible without cheap and abundant energy. I would like to share some of our conclusions and if possible, our project would benefit from your advice. Our team membership includes a rocket engineer, a nuclear engineer, a mechanical engineer and a statistician. Unfortunately, we do not have a plasma physicist. This knowledge gap has slowed our progress.

The design requirements for a spacecraft propulsion system are severe. The driver systems must be compact and low in mass and must place minimum demands on spacecraft power supply. The fuel must be storable for years or decades, which rules out the direct use of tritium. Our fuel choice is lithium deuteride. The combination of these requirements led us to abandon lasers as a potential driver technology, as poor overall efficiency in delivered energy to the pellet surface would have placed excessive demands on spacecraft power supply and ancillary equipment resulted in excessive addition to spacecraft mass. Ion based driver systems appear to provide more efficient energy transfer to the pellet surface and electrostatic accelerators could function as very compact and efficient drivers. Kinetic impact as per your design is an additional possibility.

Further studies revealed that achieving compression of cold plasma with density up to 1kg/cm3 at the centre of a pellet, would require two orders of magnitude less driver energy than creating a 20 microgram hot spot necessary for ignition. The use of electrostatic drivers could potentially deliver sufficient energy for compression of cold plasma, but the generation of a 5-10KeV hot spot would require more energy than such a driver could realistically deliver. This was due to ion scattering at the requisite current levels, imposed by a 3MeV limit on ion energy in electrostatic accelerators. Fast ignition concepts do not appear promising for a number of reasons. It would appear that your own work with kinetically driven Fusion appears to be hitting similar problems, achieving impressive plasma density, but lacking the temperatures needed for ignition.

After considering a number of different driver options, we reached a compromise that we believe will achieve ignition within the energy flux limitations imposed by the electrostatic accelerator. Our plan involves a Fusion fission hybrid approach. This requires producing solid lithium deuteride pellets, with fuel mass of 2mg, with 1mg polyethylene ablation jackets. The centre of each pellet will consist of approximately 1 microgram of enriched Uranium, plutonium-239 or americium-241. Fission provides the thermal energy needed to heat the central hot spot to a temperature of 5-10KeV. Achieving critical conditions in such a small mass requires close coupling of the fission and Fusion stages.

1) As compression proceeds, the density of the pellet fissile core increases by a factor of several hundred. Critical mass is inversely proportional to the square of fissile density, as leakage declines. At the density achieved as shockwaves converge at the fissile core, critical mass is reduced to milligrams.

2) As compression approaches its maxima at the centre of the pellet, the surrounding lithium deuteride functions as a dense and highly efficient neutron reflector further reducing critical mass.

3) As density and temperature increase close to the boundary between the fissile core and surrounding lithium deuteride, quantum tunnelling results in Fusion reactions. These generate neutrons with energy between 2.45 and 14.1MeV. Some 50% of these neutrons enter the fissile core where they result in fast fission, releasing 3-4 additional neutrons and fission fragments.

4) Some of the neutrons generated by fission cause secondary fission in the fissile core. Others stream out of the core and impact deuterium and lithium atoms in the compressed lithium deuteride charge. This generates energetic ions and lithium fission generates tritium ions.

5) The small diameter of the fissile core allows a large fraction of fission fragments to escape the fissile surface with most of their kinetic energy. Each fission fragment will deposit approximately 80MeV of energy into the surrounding lithium deuteride. Each fragment will generate thousands of lithium and deuterium ions in the KeV energy range, within 1E-6m of the fissile surface. This results in hundreds of Fusion events per fragment, yielding hundreds of neutrons. Some 50% of these neutrons enter the fissile core, where they yield additional fast fission events, sending more fission fragments into the lithium deuteride shell. The close coupling between Fusion and fission reactions leads to rapid increases in fission rate, leading to criticality even in microgram quantities of fissile material. The resulting high temperature ions generated close to the fissile surface, stream into the surrounding compressed lithium deuteride generating a detonation wave that ignites the pellet. The high neutron flux close to the core also results in substantial lithium fission, generating tritium ions.

Our initial calculations suggest that heating a 20 microgram central hot spot to ignition temperatures of 10KeV, will require approximately 0.1 microgram of fissile material. Assuming that low enriched Uranium is used, 1 microgram at the centre of a spherical pellet would be sufficient to achieve hot spot ignition. In this hybrid approach, fissile fuel represents some 5E-4 of total fuel mass and approximately 1E-4 of total energy released, assuming high burn up of both fuels. Whilst fission provides an effective trigger, it therefore yields a negligible proportion of total energy. The plasma exhaust is therefore relatively clean.

I am curious to know if your company has considered a similar Fusion fission hybrid approach to achieving pellet ignition. If so, are you aware of any problems to this approach that we have not accounted for?

Your faithfully

Peter Cassidy
CEng, MNucI, BEng, MSc.

Last edited by Calliban (2022-04-05 17:07:06)

tahanson43206 · 2022-04-06 09:41:02

For Calliban re email to Last Energy ....

Mars Society (courtesy of Executive Director James Burk) can facilitate Zoom meeting between you and a representative of the company.

I am willing to provide the connection, and am willing to stretch my schedule to meet the requirements of the parties.

A day's advance notice of the requirement would be helpful.

Also, while any of the Moderator/Administrators can admit a new member into the forum, I've been handling that for a while, and could make it happen, if that would be helpful.

(th)

Calliban · 2022-04-06 09:59:11

tahanson43206 wrote:

For Calliban re email to Last Energy ....
Mars Society (courtesy of Executive Director James Burk) can facilitate Zoom meeting between you and a representative of the company.
I am willing to provide the connection, and am willing to stretch my schedule to meet the requirements of the parties.
A day's advance notice of the requirement would be helpful.
Also, while any of the Moderator/Administrators can admit a new member into the forum, I've been handling that for a while, and could make it happen, if that would be helpful.
(th)

Thank you, I will keep that in mind. I have yet to receive any correspondence, but it may take some days if they choose to reply. I would anticipate that it will be via e-mail. Unless the company feels it has something to gain through longer term cooperation with the society, I would be surprised if they were interested in a video conference. But I will not preempt the decision. We shall wait and see how the discussion develops. If they choose to reply, we should be able to deduce from the email their interest in a longer conversation. In any event, I hope that our modest efforts here contribute in some small way to realising their goals. There is always the possibility that they had not considered a hybrid approach and that this will tease them to think in new ways. Or it may be that they did consider it and had good reasons for not pursuing this approach. We may find out in due course.

Last edited by Calliban (2022-04-06 10:05:51)

Calliban · 2022-04-11 09:36:12

It has been 1 week since the letter was sent to First Light Fusion. No response has been received yet and at this point I think a response is unlikely. I have limited ability to progress this topic much further on my own. Whilst we can be sure that fission-fusion micro explosions are workable as a propulsion concept at some scale (they are essentially mini hydrogen bombs), it is difficult to be certain of its efficacy at small scales without testing.

tahanson43206 · 2022-04-11 09:43:42

For Calliban re #37

I agree that a reply is unlikely. It is standard practice for private enterprise that receives unsolicited correspondence to file it (carefully) but NOT to reply.

Only the most extra ordinary of circumstances might have led someone to acknowledge your offer of collaboration.

However, there is nothing standing in the way of your making an application for funding to the UK Department of Energy (or whatever it is called).

I have no way of knowing what kind of organization you work for, except for hints that it is not small, and it is not in any way space related.

Ideally, your organization would want to sponsor a line of inquiry that could lead to enormous rewards for the stakeholders.

However, little in this life is ideal, so the support of your organization may not be an option.

That leaves the local government research funding.

However, pursuing ** that ** means taking some personal risk, and I have no way of knowing what your situation may be.

Best wishes for sorting out the optimum path forward.

In the next post, I'll offer a summary of a line of inquiry that is similar to those you've described, but not one that I can recall your having considered.

(th)

tahanson43206 · 2022-04-11 10:07:33

This post is offered for Calliban, but I'm hoping others may be interested and willing to contribute to development....

SearchTerm:Boron11-Hydrogen fusion
SearchTerm:Fusion Boron11-Hydrogen

The ideas presented by Calliban, and supported by reports of research by First Light, as well as by government research institutions, inspired me to think (again) about how the Boron11-Hydrogen reaction might fit into these scenarios.

Boron11-Hydrogen is well known (of course) and extensively studied. Numerous attempts have been made to bring this promising (but challenging) reaction into practical use, but so far, all efforts have failed, and I have heard of no progress that even hints at possible success.

The key concept for someone reading this for the first time to keep in mind, is that the Boron11-Hydrogen reaction requires a very specific energy of the approaching Hydrogen nucleus (Proton) to achieve capture by the Boron11 nucleus despite the vigorous objection of the respective parties due to their like charges.

I'd wondered for some time if the Boron11 atoms might be collected in a solid. The natural state of Boron (isotopes 11 and 12) is a solid.

The concept I had in mind is that if the Boron11 atoms are packaged in a solid, they are constrained in their movement by the limits of the matrix of which they are a part. Their movement to and fro could be further reduced by lowering the temperature of the solid target to as close to 0 Kelvin as is practical. In space (of course) such a low temperature is quite achievable.

The second part of the concept I've been thinking about is delivery of a quantity of Hydrogen nuclei to the target at the precise velocity needed for fusion.

A Cyclotron (invented by Ernest O. Lawrence in 1929-1930 (per Google)) is a natural fit for this task, because it can deliver output at precise energy levels.

However, as Calliban has pointed out many/numerous times, the density of the stream is of concern, and a Cyclotron may not be able to deliver the volume of Protons needed to achieve a useful output from the proposed system.

Calliban's recent discussion of adding Inertial impact to previous consideration of fission/fusion devices caught my attention.

Conceivably (and here is where I am looking for guidance) a solid mass of Boron11 atoms might be packaged (somehow) with hydrogen atoms (complete with electrons so electrically neutral) and delivered as a package to a target at the required velocity to insure the energy levels needed for fusion occur.

For reference:

A cyclotron is a type of particle accelerator invented by Ernest O. Lawrence in 1929–1930 at the University of California, Berkeley, and patented in 1932. A cyclotron accelerates charged particles outwards from the center of a flat cylindrical... Wikipedia
Cyclotron - Wikipedia
en.wikipedia.org › wiki › Cyclotron
A cyclotron is a type of particle accelerator invented by Ernest O. Lawrence in 1929–1930 at the University of California, Berkeley, and patented in 1932.
Cyclotron radiation · Cyclotron resonance · Synchrocyclotron
People also ask
What is a cyclotron used for?
Where is cyclotron used?
What is the principle of a cyclotron?
What is cyclotron in simple words?
What is a cyclotron? - Medicine, Materials, Energy and Environment
fedorukcentre.ca › resources › what-is-a-cyclotron
A cyclotron is a type of compact particle accelerator which produces radioactive isotopes that can be used for imaging procedures.
Duration: 4:55
Posted: Apr 29, 2019
Cyclotron - Hyperphysics
hyperphysics.phy-astr.gsu.edu › hbase › magnetic › cyclot
The cyclotron was one of the earliest types of particle accelerators, and is still used as the first stage of some large multi-stage particle accelerators.
cyclotron | Description, History, & Facts - Encyclopedia Britannica
www.britannica.com › Technology › Engineering › Mechanical Engineering
cyclotron, any of a class of devices that accelerates charged atomic or subatomic particles in a constant magnetic field. The first particle accelerator of ...
Principle and Working of Cyclotron - YouTube
www.youtube.com › watch
Nov 1, 2016 · It was devised by Lawrence Principle Cyclotron works on the principle that a charged particle ...
Duration: 6:45
Posted: Nov 1, 2016

For SpaceNut ... If you have time to find reports on Boron11-Proton fusion attempts, they would be welcome!
(th)

tahanson43206 · 2022-04-13 07:24:32

For Calliban re Post #37

After thinking about the situation for a couple of days, I think that a follow up inquiry may be justified.

While the volume of traffic from qualified individuals such as yourself may be low, my guess is that the (probably small) company is simply overwhelmed with the volume of traffic. That traffic will include qualified individuals such as yourself, but it will include a great number of forward looking individuals who are just curious or wanting to offer encouragement, and it will include a great number of media inquiries.

You might be able to break through the log jam if you are (gently) persistent.

In addition, it is not out of the question for you to tap into the media interest side of the house.

You are not (as far as I know) an actual "member" of the Mars Society, but you are ** certainly ** an active and valued member of the NewMars forum, and three of it's administrative staff ** are ** members of the Society.

Pending the approval of RobertDyck, SpaceNut and myself, I'd like to encourage you to re-transmit your message, and add whatever connection to the NewMars forum, or to the Society you may consider appropriate.

To start the ball rolling, you have my endorsement for your inquiry.

(th)

Calliban · 2022-04-13 07:55:27

TH, I will do.

There are other fission-fusion hybrid options that may be applicable to large ship propulsion. One option is a magnetically confined plasma core reactor, containing Uranium, lithium and deuterium ions. The plasma can be kept relatively cold compared to conventional magnetic confinement reactors, which allows for much higher density for the same magnetic pressure. Fusion events will produce neutrons. These will result in fission, either within the plasma or within surrounding Uranium blankets. Each fission event within the plasma will add 160MeV of thermal energy to the plasma. As the fission products transfer energy to the surrounding plasma, they will generate numerous Fusion events along their path. The neutrons released will generate more fission events, and so on.

The magnetic mirror concept would work well in this regard. Plasma would leak from the reactor with a dynamic pressure of up to 10 bar. The hot plasma would then mix with hydrogen propellant, which may have been preheated in the blankets, to produce a high thrust and high ISP exhaust. The engine would leak fission products. However, if we are planning to use tug vehicles between LEO and HEO, we do not need to fire the engine until we have reached high orbit. By combining fission and Fusion in this way, we can use natural Uranium as the plasma fuel and blanket material. This can be sourced on Mars.

Last edited by Calliban (2022-04-13 07:59:14)

tahanson43206 · 2022-04-13 09:19:48

For Calliban re #41

I like the idea of turning a weakness into a strength.

It ** seems ** to me this is not the first time you've described this propulsion method, but it ** seems ** (to the limits of my memory) that you are refining it as you go along. It seems to me you have lots of concepts in mind, and they appear to be interacting with each other, and with inputs from the outside world.

Your caution about running this device away from Earth leads (me at least) to revise my understanding of the work of GW Johnson.

Dr. Johnson has shown that a Tug can give a massive space craft a boost to just under Escape, and still return to Earth for it's next mission.

A revised version of that concept, taking your proposed leaky mirror "engine" into account, would use chemical propulsion to move the massive ship to GEO (or above), and then kick in the Leaky Mirror engine for that much greater effort.

The massive ship still needs to perform a small burn on it's own in this scenario.

However, if the Leaky Mirror engine is released from the tug in High Earth orbit, then it could (presumably) carry on all the way to Mars where it might even be enlisted to achieve LMO without blasting Mars itself with radiation.

Best wishes for ** more ** inspiration in coming days!

(th)

Calliban · 2022-04-13 09:57:55

In a mixed plasma like this, a large part (maybe even the majority) of energy will be generated by fission. The Fusion reactions generate a lot of fast neutrons, which will cause fission in the plasma and blankets. The advantage is a plasma that generates both high exhaust velocity and high thrust, is relatively easy to contain, does not require external heating and can generate power from depleted Uranium. On Mars, a plasma core reactor like this could start with natural Uranium and Thorium, without having to wait decades for sufficient fuel to breed.

I prefer the IC Fusion concept. It would be cleaner and have higher ISP.

Last edited by Calliban (2022-04-13 10:04:47)

Calliban · 2022-04-13 13:03:50

This is a very interesting technology.
https://en.m.wikipedia.org/wiki/Lattice … ent_fusion

An operating fission reactor produces high neutron fluxes and decaying short lived fission products generate high gamma fluxes. A capsule containing titanium deuteride in the centre of the core could generate a lot of fast neutrons. This technology could allow the production of extremely compact fission reactors, with reduced fissile loading. A useful technology for a Mars base.

Calliban · 2022-04-13 16:49:51

Two NASA papers on lattice fusion.
https://www1.grc.nasa.gov/wp-content/up … -Final.pdf
https://www1.grc.nasa.gov/wp-content/up … inal-3.pdf

This technology confines deuterium ions in the tight pores of a metallic lattice. The electrons within the lattice also provide debeye shielding, allowing nuclei to approach one another with sufficient proximity to allow quantum tunnelling to induce fusion. Fusion reactions in the lattice are induced by pumping the material with 2.9MeV electrons. These yield x-rays of the same energy upon impact. The x-rays fission deuterium ions into protons and neutrons. The neutrons then transfer kinetic energy to other deuterium ions. These then undergo fusion.

My main interest in this mechanism is its ability to provide a very compact and efficient neutron source. Fusion in both pure deuterium and in deuterium and tritium, releases a large portion of its energy in the form of neutrons. Such a dense neutron source allows the creation of very compact nuclear reactors, for both power supply and a nuclear thermal engines for large interplanetary ships. Such an engine does not need a moderator. The titanium deuteride target can be surrounded by a compact array of tungsten tubes containing metallic uranium. The fusion and fission reactions will give rise to hard neutrons, with an average energy greater than 2MeV. These will fast-fission 238U in the fuel rods. Likewise, as fission rate builds up, the neutrons and gamma from the reaction and decay of fission products, will cause more fusion events, releasing more fast neutrons. The two processes become coupled. The hard neutron spectrum and the ability of 238U to fast-fission with neutron energy >1MeV, negates the need for any enrichment of uranium. DU can be used. This means that no plutonium or fissile actinides need to be launched from Earth. The rocket will probably be operated in pulsed mode. A particle discharge into the TiD target will release a burst of neutrons, which will cause fission and raise the fuel temperature. A millisecond later, a valve will open, allowing hydrogen to flow over the fuel rods and exit the rocket. Pulsing in this way, avoids softening the neutron spectrum as the hydrogen propellant exits the engine before the next pulse is initiated.

On Mars, this technology allows us to construct very compact fast reactors. It also means that no enrichment is necessary. The reactor can be loaded with metallic natural uranium fuel in stainless steel cladding. The fuel is shuffled inward and can be discharged at a burn up of approaching 20% HM atom content. The hard neutron spectrum increases the number of neutrons produced by fission and increases the proportion of fission occurring in 238U. This has a strong positive effect on breeding ratio (238U into 239Pu) and allows a standing wave to develop within the core, effectively breeding the fuel needed to sustain the reaction within the core, without the need for reprocessing or dedicated blanket regions. This is the basic idea behind the candle or travelling wave reactor. The discharged fuel can be stored in steel casks. There will be no hurry to reprocess it, because the reactor will be loaded with natural or depleted uranium at its outer edges. It does not need to be loaded with plutonium or other fissile isotopes, because all of the fuel is effectively bred within the core as the fuel shuffles inward.

Last edited by Calliban (2022-04-13 17:36:59)

tahanson43206 · 2022-04-13 17:36:37

For Calliban re #45

SearchTerm:Lattice fusion NASA reports
SearchTerm:Fusion lattice

Thank you for distilling those long reports into text suitable for the NewMars audience!

(th)

Calliban · 2022-04-14 16:36:34

Interesting presentation on thorium based nuclear reactors from Carlo Rubia.
http://www.thoriumenergyworld.com/uploa … thec13.pdf

Calliban · 2022-04-21 12:10:44

It would appear that NASA and the US Navy have cottoned on to the Lattice Confinement Fusion Fast-Fission idea.

https://ntrs.nasa.gov/api/citations/202 … fisson.pdf

The concept as described does not require enriched uranium fuel, as the 14.1MeV fusion neutrons will fast-fission 238U or 232Th nuclei, without need for any plutonium, 235U or 233U, or indeed any breeding. The applications of this new technology are virtually endless and it's significance is hard to overstate. If it works, it heralds the beginning of a new nuclear age, providing the energy needed for deep Space settlement as well as largely displacing fossil fuels here on Earth.

This concept would work best of all for very small power applications, with power levels up to a few hundred kW. The lattice Fusion assembly would be slotted into a hollow uranium metal slug. The fusion fast neutrons would stream out of the lattice assembly. Most of those 14.1MeV neutrons will fast-fission uranium atoms, releasing energy and on average some 4.2 additional neutrons. Some of those fission neutrons will be absorbed by uranium breeding plutonium, some will fast fission more 238U yielding yet more neutrons. Others will re-enter the lattice, causing fusion and producing more 14.1MeV neutrons. To get the most out of this concept the neutron spectrum needs to remain as hard (High energy) as possible. Hence the idea of surrounding the lattice with thick uranium metal. There are no other atoms present to serve as moderator. The uranium will provide a lot of gamma shielding as well. The slug would be clad in tungsten, with cooling thins attached to the outside and immersed in a jacket of liquid sodium.

Units like this could be used to power space electric propulsion, Mars surface power, even vehicle propulsion. When burn up reaches 10%, we simply bury the whole fuel assembly. No need to reprocess, unless we have some other specific use for the isotopes in the fuel slug.

Last edited by Calliban (2022-04-21 12:46:35)

tahanson43206 · 2022-04-21 12:27:01

For Calliban re #48

Thank you for adding this new link and insight to the topic!

Will read later because busy now but certainly encouraged!

After first glance at the link provided by Calliban, I am back with this:

Low-Energy Nuclear Reactions Workshop
October 21-22, 2021

While the pdf does not show a date (that I could see at any rate) the reference provides an indication the paper is less than 6 months old.

If there is a reader who can translate this academic paper into NewMars Standard English (whatever that is) I'd be grateful.

(th)

Calliban · 2022-04-21 15:10:09

One point made within the paper, is that fission products from fast-fission are more benign (lower radiotoxicity). I had not thought about this before, but it makes sense. A fast-fission will release more neutrons than a thermal or intermediate spectrum fission. This means that the average number of neutrons remaining in fission products will be lower and they will be less radioactive. Unfortunately, a portion of those abundant neutrons will be absorbed by 238U breeding plutonium. Keeping the spectrum as hard as possible, should at least limit plutonium concentration in spent fuel, as a greater proportion of neutron impacts will fission 238U directly, rather than be absorbed breeding plutonium.

For small nuclear reactors, with a power <100MWth, lattice fusion allows us to build extremely high power density nuclear cores. These cores are small enough that they can be manufactured as cartridges. They will essentially be solid uranium metal cylinders, with tungsten cooling tubes running through them. Sodium will be forced through the cooling tubes using a submerged centrifugal pump. When burn up reaches about 100GW-days/tonne, we remove the entire core with a single lift and place it into a shielded fuel flask. A new DU core can be lifted onto the nozzle plenum on the same day that the old one is removed. This allows very high capacity factor, as refuelling would require only a day or two every few years. The high power density is also advantageous for economy, as capital costs are a function of plant size. With lattice fusion, it should be possible to build reactors with power density 1GWth/m3. A 100MWth core sufficient to power a large container ship, would be just 0.5m in diameter. The uranium itself innthe outer core would shield most of the neutron and gamma flux. The whole reactor, including lead shielding, would be approximate 1m in diameter and would weigh around 8 tonnes. Using an S-CO2 power generation loop, it would produce 50MWe of power. This is exactly the sort of power plant that would work well for a Mars base. It would be entirely non-radioactive at take off and could easily fit in a single Starship payload.

Last edited by Calliban (2022-04-21 15:34:51)

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