Liquid Fluoride Thorium Reactor

[mesa]

See also - https://www.physicsforums.com/showpost.php?p=2546513

Great link!

 

[Astronuc]

Should we be so concerned with the initial injection of fissile U235 or concentrate on the Th232/U233 breeder cycle as the majority of operational time will go to that? On another note, perhaps the easiest way to set this up would be based on MWt generated since we can directly calculate fissions per U233 (and small amounts of U235 created from the breeder cycle)

I think one has to start with U-235/Th-232 until one produces enough U-233.

I have seen interviews of the scientists from ORN suggesting that removal of tritium is not an issue, also considering the difficulty in isotopic separation of Li₆ could add a great deal of expense to a reactor on commercial scale when considering the large quantities of salt required.

Laser isotopic enrichment/selection is very advanced.

We are covering an aweful lot of ground here, what are your thoughts as far as where we should focus our energy for now?

There are a lot of technical issues in design a nuclear power system. Just take a look at the DC process. Adding a chemical separation plant in parallel just adds to the complexity (and I'm not sure that is not addressed in current licensing bases). Core and fuel design are a somewhat small but significant part of the system.

Note in WASH-1222 (TABLE I), the proposed Specific Fissile Fuel Inventory for the MSBR is 1.5 kg/MWe. So that for a 1 GWe plants, the inventory would be 1.5 Mt. If that's just the fissile content, then at 3% (by mass), the fertile inventory is about 49 Mt. It also proposes 72% LiF, 16% BeF₂, 12% ThF₄ and 0.3% UF₄ (based on moles?).

If a MSR was to be built, I'd recommend a 200 MWt system, rather than attempting a larger full scale system.

FYI - some options - http://www.gen-4.org/GIF/About/documents/30-Session2-8-Renault.pdf

 

[mesa]

I think one has to start with U-235/Th-232 until one produces enough U-233.

Okay, but I have an objection; I think we should get comfortable with calculations of products off of the Th232/U233 breeder cycle first since fissile ratios will be for the most part consistent before jumping into changing mixtures of fissile that we will see in the primary reactions as U235 is replaced by U233.

I understand that the U235 cycle comes first in operation but it would be nice to have more familiarity with running figures before diving into the shallow end of the pool.

Either way, I am ready to crunch.

Laser isotopic enrichment/selection is very advanced.

Any idea where the costs would be? Is removal of Li₆ critical for operation? If not is there value in the tritium production?

There are a lot of technical issues in design a nuclear power system. Just take a look at the DC process. Adding a chemical separation plant in parallel just adds to the complexity.

This is your field of expertise, so if you have an idea of where would be best to focus, you have my attention.

It would seem like a good idea to run numbers on the neutron poisons along with fission products that will cause issues with the materials however number of fissions of fissile must be know first (U235/Th232/U233 or the Th232/U233 cycle). What are your thoughts?

 

[mesa]

Note in WASH-1222 (TABLE I), the proposed Specific Fissile Fuel Inventory for the MSBR is 1.5 kg/MWe. So that for a 1 GWe plants, the inventory would be 1.5 Mt. If that's just the fissile content, then at 3% (by mass), the fertile inventory is about 49 Mt. It also proposes 72% LiF, 16% BeF₂, 12% ThF₄ and 0.3₄ (based on moles?).

If a MSR was to be built, I'd recommend a 200 MWt system, rather than attempting a larger full scale system.

FYI - some options - http://www.gen-4.org/GIF/About/documents/30-Session2-8-Renault.pdf

For some reason this part of your post wasn't showing before I replied :/

That is a lot of material. We will probably have to read through the ORN documents to get a better idea on whether these figures are based on mols, mass, etc. since the WASH-1222 doc came from that data.

"A 200MWt system rather than attempting a larger full scale system", it's funny to think of 200MWt as 'small'. Can you elaborate why this is a reasonable target for a test reactor?

 

[mheslep]

... In addition, the Li in the LiF should be depleted in Li-6 to minimize tritium production.

Some are proposing a sodium based salt rather than lithium for just that reason.

 

[sliebsch]

I actually chose to write a paper on this topic in undergrad. Very very interesting topic. They come with a unique set of problems, but nothing insurmountable. They use familiar, abundant materials (fluoride and thorium), and have a reliable passive safety feature(the salt plug). However, nobody in my class had ever even heard of this reactor type, even though it appears to be competitive with or even superior to LWRs in size and safety. I think more research needs to be done, that's just my two cents.

 

[sliebsch]

If I remember right, they didn't become popular because LWR technology had already been developed for submarines, so there was a great deal of research and investment momentum in that direction, even though it might not be the best option for commercial power production.

 

[Steve Brown]

Thorium reactor also produces waste. Less transuranics than uranium cycle, but about the same amount of fission products. This waste needs to be disposed off just the same.

The mass of fission products created is about the same, but it is many times smaller than the total mass of spent fuel rods. About 98% of the mass of a spent fuel rod is unreacted fissile material. On the other hand, a LFTR continuously processes the core salt to remove fission products, while leaving the fissile material in the core salt, where it can react to provide energy. There is no spent fuel assembly to dispose of, and there is no waste of valuable fissile material. In other words, there is no turning valuable fissile material into radioactive waste without deriving energy from it.

 

[nikkkom]

The mass of fission products created is about the same, but it is many times smaller than the total mass of spent fuel rods. About 98% of the mass of a spent fuel rod is unreacted fissile material.

I know that, and I already said in other thread that IMO spent fuel should be reprocessed, not buried as-is.

On the other hand, a LFTR continuously processes the core salt to remove fission products, while leaving the fissile material in the core salt, where it can react to provide energy. There is no spent fuel assembly to dispose of, and there is no waste of valuable fissile material.

This is verging on being a blatant PR.

LFTR in this regard is not better than other reactors, because processing of highly radioactive core salt is neither easy nor cheap - roughly on par with cost and difficulty of spent fuel reprocessing for LWRs.

LWR proponents can easily do the same and portray it as a weakness of LFTR: "every LFTR requires a small reprocessing plant on-site, whereas LWRs can use a common reprocessing plant, utilizing economies of scale."

In other words, there is no turning valuable fissile material into radioactive waste without deriving energy from it.

LWRs don't do it either, at least in France.

 

[Steve Brown]

This is verging on being a blatant PR.

You wrote that in response to the following statement of facts:

"On the other hand, a LFTR continuously processes the core salt to remove fission products, while leaving the fissile material in the core salt, where it can react to provide energy. There is no spent fuel assembly to dispose of, and there is no waste of valuable fissile material."

I can't help it if you don't like facts, but calling them "PR" does not make them any less true.

LFTR in this regard is not better than other reactors, because processing of highly radioactive core salt is neither easy nor cheap - roughly on par with cost and difficulty of spent fuel reprocessing for LWRs.

That sounds more like opinion than fact. Processing of solid fuel rods requires shutting down the reactor, physically removing and transporting them to a reprocessing facility. There, the rods have to be disassembled, the solid material has to be converted to liquid or gas phase in order to separate fission products and transuranic isotopes from the fissile material. Then, new fuel rods have to be fabricated at great expense, transported back to the reactor, and installed. Processing of molten core salt obviates all the steps of shutdown, removal, transport, disassembly, conversion to liquid or gas phase, fabrication, transport, installation, and reactor startup. Not only that, but continuous processing keeps the level of neutron absorbers such as xenon-135 low, whereas these poisons build up in fuel rods, necessitating replacement of the rods, for that and other reasons, after only a small fraction of the fissile material is reacted. On balance, the solid fuel cycle entails costly and wasteful inefficiencies that the molten salt reactor avoids.

I get that you don't like the molten salt reactor concept, or that you simply like to argue, but just as you insisted on staying on topic, I insist that you stick to discussing facts instead of characterizing them as "PR" or anything else.

 

[nikkkom]

You wrote that in response to the following statement of facts:

"On the other hand, a LFTR continuously processes the core salt to remove fission products..."

Really? There is a functioning LFTR anywhere? There ever was a functioning LFTR which in fact did salt processing?

It looks like our definitions of what word "fact" means are quite different.

LFTR in this regard is not better than other reactors, because processing of highly radioactive core salt is neither easy nor cheap - roughly on par with cost and difficulty of spent fuel reprocessing for LWRs.

That sounds more like opinion than fact. Processing of solid fuel rods requires shutting down the reactor, physically removing and transporting them to a reprocessing facility.

LWRs today achieve ~90% capacity factor. Looks good enough to me.

There, the rods have to be disassembled, the solid material has to be converted to liquid or gas phase in order to separate fission products and transuranic isotopes from the fissile material. Then, new fuel rods have to be fabricated at great expense, transported back to the reactor, and installed.

Why "at great expense"? Last time I checked, fuel cost is barely 10% of the costs of nuclear-generated electricity.

Processing of molten core salt obviates all the steps of shutdown, removal, transport, disassembly, conversion to liquid or gas phase, fabrication, transport, installation, and reactor startup.

And of course, it doesn't introduce any new difficulties which are not present in LWRs. There's no hot corrosive fluoride salt. There are no short-lived and therefore *extremely* radioactive isotopes like I-131, Cs-134, etc. It's all figment of my imagination.

The reprocessing plant is a piece of cake, any idiot can build one safely. We all know that. Look how Japanese had no problems building one. Look how Americans easily built one. No delays, no budget overruns.

Do you really expect that we are all ignoramuses here?

I get that you don't like the molten salt reactor concept

I'm quite happy with molten salt reactors, I don't like when people push their agenda instead of being honest and balanced.

 

[mheslep]

LFTR in this regard is not better than other reactors, because processing of highly radioactive core salt is neither easy nor cheap - roughly on par with cost and difficulty of spent fuel reprocessing for LWRs.

Processing molten salts to remove fission products may be neither easy or cheap, as you say, but at least it is feasible - with the reactor online so that high burnup also becomes feasible. Online removal of the majority of fission products with solid fuels is not feasible.

 

[mesa]

I am glad to see this thread opened back up, this is a wonderful topic.

Really? There is a functioning LFTR anywhere? There ever was a functioning LFTR which in fact did salt processing?

It looks like our definitions of what word "fact" means are quite different.

Excellent point, so how are you able to draw the following conclusions?

LFTR in this regard is not better than other reactors, because processing of highly radioactive core salt is neither easy nor cheap - roughly on par with cost and difficulty of spent fuel reprocessing for LWRs.

I think this should be broken down and each point of contention gone through point by point until there is some semblance of consensus. There will never be a test reactor built until the leg work is done and for good reason, what if the promises of LFTR are not what they seem? What if they are?

Throwing out conjecture does no one any good, and I am not pointing fingers; I have been guilty of this myself.