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We have several topics that include "fission" in the title, but there is none appropriate to the announcement that will be offered in post #3.
This topic is offered for NewMars members to report news of developments in the field of fission-only reactors, or to comment.
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This post is reserved for an index to posts that may be contributed by NewMars members over time.
Calliban: ADR Accelerator Driven Reactor
https://newmars.com/forums/viewtopic.ph … 04#p229404
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This post is about what appears to be encouraging news for a small reactor that may eventually qualify for use in populated areas:
https://interestingengineering.com/ener … 23_11_24_3
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The accelerator driven reactor (ADR) is an interesting concept.
https://en.m.wikipedia.org/wiki/Acceler … al_reactor
Carlo Rubio advocates what he calls an Energy Amplifier. This is a spallation driven nuclear reactor. A particle accelerator is used to accelerate a beam of protons to 1GeV. The protons collide with lead nuclei inside a nuclear reactor core. A collision at this energy will almost completely disintegrate a heavy nucleus, releasing a dozen or more neutrons. These neutrons are then absorbed by thorium nuclei in a fuel blanket surrounding the spallation source. The 232Th transmutes into 233U, which is fissile. When spallation neutrons impact 233U, energy is generated by fission. Fission releases even more neutrons, causing more fission and transmuting more 232Th into fissile 233U.
This type of reactor is useful, as in addition to generating power its discharged fuel would contain enough fissile 233U to fuel several downstream nuclear reactors of comparable power. On Mars we could use these devices to breed 239Pu and 233U from native or imported uranium and thorium. One interesting feature of spallation sources is that the number of neutrons produced by disintegration increases as the atomic weight of the target nuclei increases. This means that higher actinides in long-lived nuclear waste are even better targets than lead. Far from being waste, this material provides us with a useful source of neutrons. On Earth, this technology could allow the expansion of light water reactor fleets without concerns over uranium depletion. On Mars, the use of ADRs allows rapid expansion of nuclear power supply. It also allows 100% of the energy content of uranium and thorium to be extracted. This is important if uranium and thorium turn out to be rare on Mars or if we are importing these fuels from Earth.
On Mars, we would load an ADR with uranium or thorium metal fuel, clad with stainless steel. The reactor would be cooled with ducted sodium coolant channels or liquid lead. Fuel would be shuffled inward, with the innermost blankets discharged at perhaps 5% atom burnup. The resulting discharged fuel would be about 75% thorium, 5% fission products and 20% 233U. The metallic fuel would then be dissolved in nitric acid. Fission product nitrates would be extracted and vitrified as waste. The remaining mix of uranium and thorium nitrate would be blended down with additional thorium nitrate. This 5% 233U nitrate liquor is then used as fuel for unity breeding ratio aqueous homogenous reactors. The nitrate liquor from the ADR effectively provides a starter core for new reactors. This allows nuclear capacity to expand quickly to meet the energy needs of a rapidly growing Martian colony.
Last edited by Calliban (2025-01-28 10:05:29)
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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Additional: The Belgian government started construction of a lead-bismuth cooled spallation driven reactor last year.
https://www.myrrha.be/
Belgium is a country of 10 million people. Their ability to pursue this gives me confidence that it should also be possible for a Mars colony when population reaches a similar level. Early Mars reactors will most likely be modular light water reactors using fuel imported from Earth. But beyond a certain level of development, it makes sense to start using domestic resources and to extract as much energy from uranium and thorium as is physically possible.
An accelerator driven system can work in a number of different ways. A proton beam can directly transfer energy to a heavy nucleus causing it to break up into smaller pieces, including neutrons. These neutrons then cause fission and nuclear transmutation. Alternatively, a high energy proton beam can generate muons or anti-protons. Muons can catalyse fusion in a suitable target, releasing very fast neutrons. Anti-protons are a powerful spallation source. Upon impacting a heavy nucleus, they release almost 2GeV of energy, breaking the nucleus apart and releasing a great many neutrons. I am uncertain as to which neutron source is best. They all require high energy protons to work, so the best neutron source is the one that produces the most neutrons per MJ of energy input to the accelerator.
One substantial advantage that an ADR offers is safety. The reactor is subcritical, with additional neutrons provided by the electrically driven accelerator. Rapid reactor shutdown can be achieved by cutting power to the neutron source. This can be done more rapidly than mechanically inserting control rods. This design feature could be especially useful for certain types of nuclear reactor. The gas cooled fast reactor for example, has advantages of being an extremely compact direct cycle CO2 cooled reactor, with a hard neutron spectrum and high breeding ratio. A weakness with this reactor type is that a coolant leak removes moderation from the reactor, hardening the neutron spectrum, causing power to surge. An accelerator driven reactor could solve this problem, by tripping the accelerator if neutron count increases outside a pre-defined range.
Last edited by Calliban (2025-01-28 10:29:01)
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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Metallic nuclear fuels are now being considered for light water reactors.
https://www.neimagazine.com/advanced-re … -11283875/
This has a number of near term advantages. Metallic fuels have improved thermal conductivity and fissile density. This may ultimately allow higher power density reactors. Conversion ratio will also be slightly improved.
Another advantage that is less frequently discussed, is that metallic fuels are substantially easier to reprocess using pyroprocessing. The sent fuel pellets can be melted within a crucible and mixed with liquid cadmium. Fission products dissolve into the cadmium. The actinides are denser and remain seperate, allowing them to be cast into fresh fuel pellets.
This technology is especially interesting for the thorium fuel cycle. Fuel pellets can be made from uranium thorium zirconium alloy. Pryro fuel processing techniques are far more compact and suitable to automation than classic chemical plant reprocessing. This makes it realistic to consider onsite reprocessing within manual handling of fuel. It means that Martian based nuclear reactors can be based upon conventional light water designs and Martian thorium can be integrated into the fuel cycle relatively easily.
Last edited by Calliban (2025-02-14 07:19:40)
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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