Energy From Thorium Discussion Forum

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PostPosted: Dec 31, 2013 10:12 pm 
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I've watched a lot of videos from Kirk Sorensen and others about molten salt reactors and one thing I saw as a problem for a nation that wanted to start out in nuclear power is access to enriched uranium. Molten salt reactors can run on natural uranium or thorium but to get started they need a seed fuel of U-235, U-233 or Pu-239. I'm thinking of a situation where a nation that wants nuclear power but either does not want to rely on another nation selling them fissionable material or cannot find a nation willing to export it.

Another problem might be where traditional enrichment techniques are expensive and/or might raise issues from international non-proliferation treaties. The UN does not like it when nations start building centrifuges for enrichment of uranium, that's getting too close to weapons production. Reactors designed for production of plutonium are also frowned upon because of the possibility for use in weapons.

I realize one potential solution is the building of a heavy water solid fuel reactor like CANDU could be used to provide the seed fuel. This also has an added benefit of being a design that can produce the seed fuel as well as power. Any fuel produced in a CANDU would have enough "bad" isotopes to make it useless for weapons. This sounds to me like a rather expensive solution. I have no idea on how much this stuff costs but in my mind building a CANDU sounds just as expensive as running centrifuges. It also does not avoid all the problems of solid fuel reactors that this theoretical nation wanted to avoid.

I have other ideas. I also should point out that I am not a nuclear or mechanical engineer, I am a computer engineer, so I know my ideas probably won't work but I'll bring them up here to see what I missed and see what others might offer as more reasonable solutions.

One idea I have is for this theoretical nation is to construct a molten salt reactor, fill it up with thorium salt and... wait. Given enough time there would be enough spontaneous fissions to get critical. Okay, probably not but maybe it would work.

Another idea I have is to have a fusion-fission hybrid design. Current fusors are no good at making power but they are good at making heat and neutrons. My idea would to have a variation on the two fuel LFTR design. In the center I'd have a Farnsworth fusor to generate the neutrons for the blanket salt. Given enough time the blanket would soak up enough neutrons to become critical or at least close enough to critical that the fusor would be there as a means to control the reactor, turn off the fusor and the reactor shuts down.

This fission-fusion molten salt reactor design seems simple enough that I thought of it so I doubt I'm the first to think of it. What important detail did I miss?

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PostPosted: Jan 01, 2014 12:00 pm 
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If you want to get an MSR without enrichment then the easiest way would be to build a single CANDU, run it with agressive reprocessing to build up a stockpile of relatively high grade plutonium and then use that as your seed fuel.

But that would take a while.


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PostPosted: Jan 01, 2014 1:53 pm 
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E Ireland wrote:
If you want to get an MSR without enrichment then the easiest way would be to build a single CANDU, run it with agressive reprocessing to build up a stockpile of relatively high grade plutonium and then use that as your seed fuel.

But that would take a while.
It would also be extremely costly, because CANDU fuel bundles are made of zirconium alloy and filled with ceramic fuel pellets: It is not designed to facilitate reprocessing, but to optimize heat transfer for power production.

Reprocessing is made easier if the fuel is metallic instead of ceramic -- as for example in GE's IFR or TerraPower's TWR designs (IFR is intended to use electrochemical "pyroprocessing", while TWR fuel is to use simpler "melt-refining" only).

But CANDU-type reactors will work on natural uranium fuel in liquid form of appropriate type: There's nothing that says that the fuel has to be solid.


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PostPosted: Jan 01, 2014 4:14 pm 
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E Ireland wrote:
If you want to get an MSR without enrichment then the easiest way would be to build a single CANDU, run it with agressive reprocessing to build up a stockpile of relatively high grade plutonium and then use that as your seed fuel.


What if this theoretical country wanted to take advantage of their abundant thorium reserves? A CANDU reactor can be used to breed U-233 as well as Pu-239, no? Isn't that what India and Canada have been experimenting with?

E Ireland wrote:
But that would take a while.


Define "a while". Are we talking months, years, or decades? I imagine that breeding thorium into fissile fuel would take months if only because of the need to allow protactinium to decay.

I'm thinking of nations with sufficient technology and industrial capacity that they are able to do things like drill for oil off-shore, build cars and seaworthy vessels. Nations with existing mining infrastructure that digging up thorium or uranium would not be a great leap. Perhaps they already mine for copper, gold, coal, or diamonds. A nation that realizes that they would be much wealthier if they could avoid having to purchase coal or refined petroleum from another nation. A nation that does not want to have to rely on another nation for its energy needs no matter what form it takes, be it oil, coal, or uranium. A nation that does not want nuclear weapons if only to avoid the political scrutiny that nuclear weapons brings. I can think of numerous nations that might fit this description.

I'm just think that if I were the president, prime minister, or benevolent dictator of such a nation then what would be the best means to direct my theoretical nation into having safe, reliable, and nonweaponizable (is that a word?) power.

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PostPosted: Jan 01, 2014 4:58 pm 
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You have to consider that MSR development in the early stages is not going to be done by nations without an existing nuclear program. I agree that in this point in time it's difficult for developing nations to obtain enriched fissile material (Iran, for example) but the standpoint of the international community might change over the next couple of decades if we were to see significant mutations in the nuclear field. This problem isn't unique for a country trying to start up an MSR project, but nuclear programs in general. The hostility of the international community is also largely dependent on the reputation of the nation; a Czech republic will obviously encounter less issues. Non-proliferation treaties should definitely play a role.


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PostPosted: Jan 01, 2014 5:45 pm 
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Kurt Sellner wrote:
E Ireland wrote:
If you want to get an MSR without enrichment then the easiest way would be to build a single CANDU, run it with agressive reprocessing to build up a stockpile of relatively high grade plutonium and then use that as your seed fuel.


What if this theoretical country wanted to take advantage of their abundant thorium reserves? A CANDU reactor can be used to breed U-233 as well as Pu-239, no? Isn't that what India and Canada have been experimenting with?

Define "a while". Are we talking months, years, or decades? I imagine that breeding thorium into fissile fuel would take months if only because of the need to allow protactinium to decay.


And where will your fissile startup come from?
There are no feasible fissile sources that can be obtained without a reactor or an enrichment plant.

It would likely take several reactor years.


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PostPosted: Jan 01, 2014 5:48 pm 
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jaro wrote:
E Ireland wrote:
If you want to get an MSR without enrichment then the easiest way would be to build a single CANDU, run it with agressive reprocessing to build up a stockpile of relatively high grade plutonium and then use that as your seed fuel.

But that would take a while.
It would also be extremely costly, because CANDU fuel bundles are made of zirconium alloy and filled with ceramic fuel pellets: It is not designed to facilitate reprocessing, but to optimize heat transfer for power production.

Reprocessing is made easier if the fuel is metallic instead of ceramic -- as for example in GE's IFR or TerraPower's TWR designs (IFR is intended to use electrochemical "pyroprocessing", while TWR fuel is to use simpler "melt-refining" only).

But CANDU-type reactors will work on natural uranium fuel in liquid form of appropriate type: There's nothing that says that the fuel has to be solid.


Neither of which can be practically used with thermal reactors.
These systems are only practical because fast reactors can accept significant contamination of the fuel sources.
It is very hard to beat PUREX/FLUOREX type processes for thermal reactor reprocessing.


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PostPosted: Jan 01, 2014 6:05 pm 
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For thermal breeders, maybe. For thermal converters, pyroprocesses are just fine and in fact preferable due to a large number of reasons. Distillation of the actinide metals gets pretty good seperation except for a few fission products.

PUREX/FLUOREX doesn't work with fresh fuel. It should be very easy to beat PUREX because it is a process that was designed to create weapons grade plutonium, not produce commercial power reactor fuel.


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PostPosted: Jan 01, 2014 6:29 pm 
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E Ireland wrote:
And where will your fissile startup come from?
There are no feasible fissile sources that can be obtained without a reactor or an enrichment plant.


I was under the impression that CANDU did not require any fissile seed fuel. Thinking about it I'm guessing that the Canadians had enough access to research reactors and American enriched fuel that getting any required seed fuel for CANDU was trivial.

Any nation with the capability to construct a MSR should also be capable of producing some sort of fissile material through something like a particle accelerator.

E Ireland wrote:
It would likely take several reactor years.


There's my answer! So even if some nation was capable of building MSRs they'd have to have a decade of experience in nuclear experimentation to have enough material to start a MSR.

Getting back to my idea of using a fusor to bombard suitable material with neutrons, such as natural uranium or thorium, to breed something fissile. Building a Farnsworth fusor seems simple enough, people are building them in their basements. Is using a Farnsworth fusor something that a nation starting out in nuclear power would consider as a means to create fissile material? Using solid targets and one could batch process the target material. Use of a liquid target and continuous processing would be possible. The liquid target doesn't have to be molten salt, it could be uranium salts dissolved in water. Bonus to bombarding uranium in water is that one would get plutonium and heavy water, both useful in nuclear reactors.

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PostPosted: Jan 01, 2014 7:27 pm 
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E Ireland wrote:
Neither of which can be practically used with thermal reactors.
These systems are only practical because fast reactors can accept significant contamination of the fuel sources.
All the world war two era reactors in Hanford used metal fuel -- and they were graphite moderated thermal reactors.
All the light water reactors powering US nuclear submarines use metal fuel.

Candu-style fuel channel heavy water moderated reactors would certainly work on natural uranium -- metal or fluoride salt.
It would work better than the old Hanford reactors, because D2O is a much better moderator and because fluid fuel allows continuous removal of neutron absorbing fission products - particularly the gaseous ones like xenon.


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PostPosted: Jan 01, 2014 7:42 pm 
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Metal Fuel is not the issue, the issue is gaining sufficient decontamination in the reprocessing process.
Magnox used metal fuel too for instance.

Despite what many claim about how amazing pyroprocessing is the fact remains that no significant scale pyroprocessing plant has been operated on anything close to a commercial basis.

Even the fuel for the LMFBRs in Russia has been reprocessed by PUREX at Mayak.


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PostPosted: Jan 01, 2014 7:49 pm 
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Kurt Sellner wrote:
E Ireland wrote:
And where will your fissile startup come from?
There are no feasible fissile sources that can be obtained without a reactor or an enrichment plant.


I was under the impression that CANDU did not require any fissile seed fuel. Thinking about it I'm guessing that the Canadians had enough access to research reactors and American enriched fuel that getting any required seed fuel for CANDU was trivial.

Getting back to my idea of using a fusor to bombard suitable material with neutrons, such as natural uranium or thorium, to breed something fissile. Building a Farnsworth fusor seems simple enough, people are building them in their basements. Is using a Farnsworth fusor something that a nation starting out in nuclear power would consider as a means to create fissile material? Using solid targets and one could batch process the target material. Use of a liquid target and continuous processing would be possible. The liquid target doesn't have to be molten salt, it could be uranium salts dissolved in water. Bonus to bombarding uranium in water is that one would get plutonium and heavy water, both useful in nuclear reactors.


Remember that Natural Uranium is 0.7% fissile to start with.
Thorium is entirely non fissile.

As to using particle accelerators and fusors for neutron sources, they tend to be far more expensive than a heavy water or graphite moderated reactor running on natural uranium.


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PostPosted: Jan 01, 2014 8:40 pm 
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E Ireland wrote:
Metal Fuel is not the issue, the issue is gaining sufficient decontamination in the reprocessing process.
Sufficient for what ?

CANDU reactors get about 8000 MWd/tHM of burnup without ANY "decontamination" at all.
Of course it's a whole different ball game, if you're talking about building bombs.


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PostPosted: Jan 01, 2014 8:41 pm 
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Heavy water is also an isotope enriched material. However there are no radioactive materials involved. Graphite is the material used for moderation in the initial reactors.
You could use the metallic uranium-Graphite piles to irradiate uranium and use electrolysis or chloride volatility for separation of plutonium.
With plutonium-enriched uranium, you could use calandria design of Candu with light water to produce power. It is just a boiler configuration with double walled tubes.
Time to produce enough plutonium would depend on the number of piles used-years or decades.


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PostPosted: Jan 01, 2014 10:00 pm 
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E Ireland wrote:
Remember that Natural Uranium is 0.7% fissile to start with.
Thorium is entirely non fissile.


Right, natural uranium would be a preferred fuel because of that. Stupid newbie question, where does the first neutron come from in a CANDU? I guess my question applies to all reactors really. What I mean is that a reactor is critical once the number of neutrons is such that for every neutron ejected in fission there is enough neutrons to create another fission but something has to toss that first neutron to get the chain reaction going. Is spontaneous fission of the U235 enough to start the reaction?

E Ireland wrote:
As to using particle accelerators and fusors for neutron sources, they tend to be far more expensive than a heavy water or graphite moderated reactor running on natural uranium.


Could you explain this further? Seems to me that making a Farnsworth fusor is easy and cheap enough that people build them as a hobby. Operating them for a long period of time does sound like it'd be expensive though, especially if done in a manner sufficient for mass production of fissile material. I don't understand how this would be prohibitively more expensive than a heavy water water reactor.

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Disclaimer: I am an engineer but not a nuclear engineer, mechanical engineer, chemical engineer, or industrial engineer. My education included electrical, computer, and software engineering.


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