Energy From Thorium Discussion Forum

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PostPosted: Jul 25, 2014 12:25 am 
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Higher addition of UCl4 to fuel salt will reduce M. Pt, if required.Coolant salt could also be used as a thinner.
UK has enough stocks of reactor grade Pu so the consumption of fissile is not a problem. Use of Cl37 could be considered to improve neutron efficiency later.
Will the UK have political will to try this route to utilize their Pu stocks?


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PostPosted: Jul 25, 2014 5:29 am 
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jagdish wrote:
Higher addition of UCl4 to fuel salt will reduce M. Pt, if required.


Yes, its surprising that they didn't go this route. Say a 40-50% UCl4 would still leave plenty for reducing action (UCl3) and fissile Pu (PuCl3).

Quote:
Coolant salt could also be used as a thinner.


Yes, but that option reduces HM content which takes away one of the main advantages of this concept. Unless of course you use a really volatile diluent, but that doesn't seem safe to me (vapor pressure in the fuel rods).

I also think they should switch to NaF-ZrF4 coolant. Better known, and less nasty KF activation. They could operate on 600C to go easy on materials.


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PostPosted: Jul 25, 2014 12:51 pm 
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jagdish wrote:
Higher addition of UCl4 to fuel salt will reduce M. Pt, if required.
But it isn't required.
This is just for venting volatile fission products during operation.
There is no mechanical equipment inside the fuel tubes, that would get fouled up by solidifying salt.


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PostPosted: Jul 25, 2014 1:52 pm 
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jaro wrote:
jagdish wrote:
Higher addition of UCl4 to fuel salt will reduce M. Pt, if required.
But it isn't required.
This is just for venting volatile fission products during operation.
There is no mechanical equipment inside the fuel tubes, that would get fouled up by solidifying salt.


Loss of fuel homogeneity is a major issue for molten fuel reactors, if it occurs. Even if there's no safety problem, this sort of thing will ruin reactor stability, as Pu rich phase seperates from Pu poor phase etc.

This kind of externally cooled design needs the fuel to be always liquid or always solid. In between is a no-no.


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PostPosted: Jul 25, 2014 7:13 pm 
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Cyril R wrote:
Loss of fuel homogeneity is a major issue for molten fuel reactors, if it occurs.
Well, if it did in fact occur, then I guess we wouldn't need electrochemical "pyroprocessing" on chloride salts to separate out the fuel.

And even WITH the processing, U + TRU remain unseparated - an important nonproliferation consideration in fuel reprocessing technology.


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PostPosted: Jul 26, 2014 2:13 am 
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jaro wrote:
Cyril R wrote:
Loss of fuel homogeneity is a major issue for molten fuel reactors, if it occurs.
Well, if it did in fact occur, then I guess we wouldn't need electrochemical "pyroprocessing" on chloride salts to separate out the fuel.

And even WITH the processing, U + TRU remain unseparated - an important nonproliferation consideration in fuel reprocessing technology.


The issue is with unpredictable reactor operation from concentrating fissile in one place and depletion in another. If you operate close to the melting point, you get all sorts of weird zone refining and liquid enriching processes going on. There are all sorts of secondary effects to worry about, from thermal cycling of the cladding to cold shutdown margin issues (frozen fuel salt is denser so a lot more reactive). To be safe, I'd say use a fuel salt in the tubes that has a lower mp than the coolant salt. The other option is solid fuel like thorium-uranium-plutonium alloy fuel, where the melting point is so high it will always be solid (mp above bp of coolant salt).


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PostPosted: Jul 26, 2014 11:54 am 
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Cyril R wrote:
Loss of fuel homogeneity is a major issue for molten fuel reactors, if it occurs.
If the system was permitted to slowly cool while subcritical I could see some issues arising as some fuel components solidify selectively. During operation the high delta T within the fuel will promote vigorous thermal circulation which will tend to keep things well mixed. On the flip side I wonder how the accumulation of noble metals will play out as they will tend to accumulate at the bottom of the tube. I presume that will be a contest between the rate of accumulation and the speed of decay reducing the local heat generation.


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PostPosted: Jul 26, 2014 12:35 pm 
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Lindsay wrote:
Cyril R wrote:
Loss of fuel homogeneity is a major issue for molten fuel reactors, if it occurs.
If the system was permitted to slowly cool while subcritical I could see some issues arising as some fuel components solidify selectively. During operation the high delta T within the fuel will promote vigorous thermal circulation which will tend to keep things well mixed. On the flip side I wonder how the accumulation of noble metals will play out as they will tend to accumulate at the bottom of the tube. I presume that will be a contest between the rate of accumulation and the speed of decay reducing the local heat generation.


There shouldn't be a problem with noble metals. Even if they all sink to the bottom, they will make less heat/volume than critical fuel salt so it can't run into thermal limits. It's likely that the noble metals would be very finely dispersed nano-particles that actually improve convective heat transfer.

I think the problem is with critical power during both normal operation and during extended shutdowns. It would be very difficult to prove the safety case when part of the fuel is melting or freezing all or even some of the time.


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PostPosted: Jul 26, 2014 12:40 pm 
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Cyril R wrote:
It would be very difficult to prove the safety case when part of the fuel is melting or freezing all or even some of the time.
I think that you've captured the issue perfectly with that statement, it would be challenging to prove that is NOT a problem AND could never be a problem.


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PostPosted: Jul 31, 2014 12:16 am 
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So, do the jury agree with the idea? I wish the UK (and others) get something simpler and cheaper than the EPR. Nuclear is being priced out of the market at many places.


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PostPosted: Mar 08, 2015 11:01 pm 
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jagdish wrote:
Cross-fertilization of ideas between various reactor designs could lead to interest solutions (and related problems).
A molten salt (or lead) link as secondary coolant in sodium cooled fast reactors could provide substantial safety against sodium fires.
A water coolant-moderator in the tubes, like water tubes in a boiler, could really simplify the SMSR further. However, the tubes will have to handle, beside the thermal shock, the neutron flux, and salt or lead corrosion.
Engineering could provide the key to economical nuclear power.



You just described the "Dual-Fluid Reactor" recently proposed by a german team. I have started discussion on it in this section of the forum. Would really like comments from all in this thread!!

It achieved the delayed neutron fraction containment of the MOLTEX design with better use of coolants...


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PostPosted: Mar 15, 2015 8:27 am 
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A simple, low cost fast MSR is a requirement of the time. The UK have a lot of recovered plutonium to power these. They should lead the development. US with biggest used fuel problem could follow them eventually.Only the development abroad can give some hope of US approval of a new design.
Another development urgently required is an economical reprocessing based on chloride/fluoride volatility and electro-refining. This could be off-shored.


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