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Post by Greg Kaan on Sept 19, 2016 10:00:59 GMT 9.5
Has anyone found much information on this? From a conceptual viewpoint, I like the separation of concerns with the fueling and cooling functions being performed by different fluids. The stated advantages over normal MSRs are - High operating temperature due to the boiling point of lead
- High power density due low fuel dilution
- Low neutron moderation of lead vs sodium due to small cross section for fast neutrons
- Low neutron moderation of chlorine vs fluorine due to smaller cross section for fast neutrons
- Safe neutron transmutation of lead
- Lower transmutation of reactor components due to fast neutron spectrum
- Coolant and fuel circulation speeds can be optimised for various situations (transmutation/breeding)
- Fuel circulation can be low enough for on-line pyro reprocessing
- Lower reactivity of lead vs sodium
- Lower reactivity of chlorine vs fluorine
- Small core size
- Increased neutron flux for better breeding/transmutation
It probably needs more development than the "normal" single fluid MSRs where the fuel also acts as the coolant but long term, it seems to have compelling advantages. festkoerper-kernphysik.de/dfr.pdfdual-fluid-reactor.org/Thoughts?
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Post by Roger Clifton on Sept 19, 2016 12:35:52 GMT 9.5
Separation into two fluids allows the designer to minimise the volume containing the fuel and its fission products while having the freedom to maximise the volume of coolant.
A smaller fuel volume presumably simplifies the plumbing and reduces the nooks and crannies for radioactive scale to deposit. Similarly it would be easier to ensure the containment of xenon and other volatile fission products.
Freedom with the volume of (lead) coolant would simplify the design of the heat exchanger/steam generator, possibly allowing passive (convective) circulation. In the EBR2, its large volume of coolant served as a heat sink, allowing the power and steam production to be temporarily out of sync.
I have yet to come across a discussion of the problems of scale in the plumbing of liquid (chloride)fuel, though they must certainly exist. Similarly corrosion at some level must occur with the enormous chemical variety in the fission products, and we have yet to hear about that, too. For that matter, I would also like to hear what they mean by "online pyro reprocessing", as it seems to be a complication in a part of the system that needs to be of maximum simplicity.
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Post by Greg Kaan on Sept 19, 2016 13:36:50 GMT 9.5
From my viewpoint, the on-line pyro reprocessing is an option opened up by the design but isn't inherent in the design - it's just that the independence of the fuel flow from cooling requirements opens up the possibilities for it.
Fluorine is generally more reactive than chlorine so I would expect that there are more options for plumbing materials. But yes, there has been more experience with fluorine salt fueling although none of it has been outside research facilities AFAIK.
I see this as a promising long term option that will hopefully attract sufficient funding for the potential issues to be properly investigated. I certainly would not expect it to beat the IMSR to the market but it may beat a breeding LFTR.
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Post by eclipse on Sept 19, 2016 15:12:37 GMT 9.5
Maybe it's a typo or my own misunderstanding, but aren't LFTR's using fluoride, not flourine? Isn't flourine totally crazy reactive? (Just from Kirk Sorenson rants, I don't have any physics or chemistry of my own to draw on). So this is a liquid lead FAST reactor as opposed to a liquid flouride thorium reactor running in the thermal spectrum? Sorenson has a whole thing about why thermal is better than fast to do with fuel burning efficiency, and starts at 24 minutes. But the stuff about the discovery of thorium is really cool and worth watching, and starts at 16 minutes. Please don't miss that story! www.youtube.com/watch?v=P9M__yYbsZ4Also, does this lead reactor have the same passive safety feature of 'drain away' safety to a safe drain tank that the MSR / LFTR has?
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Post by David B. Benson on Sept 19, 2016 15:19:56 GMT 9.5
Wikipedia has a page on lead-cooled fast reactor designs. This one is mentioned.
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Post by David B. Benson on Sept 19, 2016 15:23:06 GMT 9.5
Eclipse --- The company information specifically states there is no drain as, they state, the drain concept has safety issues.
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Post by Roger Clifton on Sept 19, 2016 16:48:13 GMT 9.5
Eclipse, you are quite right. There is a chemical difference between reactive "fluorine" and inert "fluoride". Similarly, between "chlorine" and "chloride". Their documentation says they prefer liquid chlorides to liquid fluorides, because neutrons lose less energy to the (heavier) nuclei of the chloride ions, also the chloride boiling points are lower for many of the elements that they want to distil.
Given the circumstances, I would expect the still to consist of an inline upright chamber with various heating and cooling arranged vertically to volatilise then capture the different vapours as they condense again. But we need to hear quite what will be separated and why.
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Post by eclipse on Sept 19, 2016 17:15:16 GMT 9.5
I like the idea of liquid salt that will drain away in an emergency, or even just drain out into the containment room if someone shot a RPG at it, and dry hard and *settle* in the reactor room. I like the idea of all the nuclear fuel being bound up in salts that can dry on the location with ... what's it called... thermo inequilibrium? so that the fuel expands as it gets too hot, and cuts out some of the reactivity? The PR advantages of the MSR with this 'drain away' safety features might be worth it over the double-fuel complexity of whatever this other company are doing.
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Post by David B. Benson on Sept 19, 2016 18:29:35 GMT 9.5
I was wrong. The conference contribution pdf clearly shows a melting drain plug. So loss of local electricity results in the actinide fluid draining into a non-critical configuration tank.
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Post by Greg Kaan on Sept 19, 2016 21:41:14 GMT 9.5
There is a chemical difference between reactive "fluorine" and inert "fluoride". Similarly, between "chlorine" and "chloride". Since the discussion is about the halogen component of the halide salt, it doesn't matter if you refer to the chemical element (fluorine/chlorine) or the ionised form (fluoride/chloride). Within the salt, the form of halogen is ionised but that's implicit. It's not like a chemical containing fluoride/chloride does not contain fluorine/chlorine atoms. Page 7 of the document describes the frozen fuel salt plug as well as being pictured in figure 2 we need to hear quite what will be separated and why. The still is for the pyrolytic separation of waste elements and produced isotopes from the fuel to avoid having to close down for refuelling but without it, fuel replacement could still be done with a bypass loop. I think Sorensen's involvement with the LFTR makes him a strong advocate of that design but this DFR design could overcome the smaller cross section for fast neutrons through its higher neutron flux. Maybe. I think there are good prospects for both designs but development is still needed before either are close to commercialisaton - for all the talk about the LFTR, there still hasn't been one operated, yet.
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Post by Roger Clifton on Sept 20, 2016 8:40:36 GMT 9.5
Greg Kaan, yes, in an ionic melt, we speak of a "chloride ion" and "chlorine nuclei" with no risk of confusion. However, Eclipse's concern that free halogen gas might be present is relevant if in-line electrolysis or superheated distillation is planned.
I cannot see any justification for in-line processing when it be could more simply performed off-line. Or in a bypass perhaps, but it would not be feasible to put fully in-line the electroprocessing of the IFR, where the actinide mix is collected off into a liquid cadmium bath and the fission products are discarded with the chloride melt. That would imply a single cycle for the fuel, but the impression is of many cycles through the moderation zone. (They don't speak of moderation, but how else do they plan to control the device?). And fractionation by distillation seems no more feasible, as the many FP chlorides must have BP's above, below and among the actinide chlorides. So what are they dreaming of?
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Post by Greg Simpson on Sept 20, 2016 15:20:30 GMT 9.5
Maybe it's a typo or my own misunderstanding, but aren't LFTR's using fluoride, not flourine? Isn't flourine totally crazy reactive? (Just from Kirk Sorenson rants, I don't have any physics or chemistry of my own to draw on). LFTRs use fluorine to convert tetrafluorides into hexafluorides for removal. Nasty stuff, but so is some of what is removed. I think this can be engineered to be safe but it's one more thing to be aware of. The liquid chloride reactor either does things the same way, presumably also using fluorine, or uses something called "molten salt electrorefining", which I know nothing about.
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Post by Greg Kaan on Sept 21, 2016 18:43:12 GMT 9.5
It's totally unmoderated, except by a minor degree by the chloride in the fuel salt. The temperature coefficient is supposed to be so deeply negative that normal control is via the circulation rate of the coolant - slowing down the coolant flow raises the temperature, reducing the fission rate. Shutting down the reactor is performed by removing the cooling from the salt plug, dumping the fuel.
This is all in the document I linked in the 1st post.
As for the online pyroprocessing, it does seem to be more integral to the design than I first thought since the safety is partly achieved by removal of actinides from the fuel so residual heating is low if the fuel is made sub-critical. The details for the pyroprocessing that you are after are not provided. Perhaps this is kept a commercial secret.
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Post by David B. Benson on Sept 22, 2016 3:50:52 GMT 9.5
The work of the Koreans on pyroproccessing is well documented. The similar design by TransAtomic includes a pyroproccessing bypass. That documentation states just that the liquid and continuous pyroproccessing is being worked on by an international team.
I suspect nobody has a viable process at this time.
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