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PostPosted: Nov 10, 2012 7:50 am 
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Wow. I can't help thinking "Rube Goldberg".

I got to the part where it was discussing the fuel plates and it said to include particles of poison. I couldn't help thinking, "if you have to poison your own reactor, maybe you need a new paradigm."

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PostPosted: Nov 10, 2012 8:57 am 
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KitemanSA wrote:
Wow. I can't help thinking "Rube Goldberg".

I got to the part where it was discussing the fuel plates and it said to include particles of poison. I couldn't help thinking, "if you have to poison your own reactor, maybe you need a new paradigm."


There´s nothing really Rube Goldberg about it, all solid fuelled reactors have this tradeoff between running longer (economics) and running with high neutron efficiency (no poison, but run shorter batches with more refuelling). Running the reactor with higher burnup is better for fuel efficiency, so if you need to add some poison the effect may still be positive on fissile consumption.

Most of today´s reactors operate with some burnable poison. CANDUs don´t have to because of the low burnup and online fuel shuffeling-refuelling.

Liquid fuelled reactors of course have many fewer issues here, they can add fuel online as required.


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PostPosted: Nov 10, 2012 10:05 am 
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Cyril R wrote:
KitemanSA wrote:
Wow. I can't help thinking "Rube Goldberg".

I got to the part where it was discussing the fuel plates and it said to include particles of poison. I couldn't help thinking, "if you have to poison your own reactor, maybe you need a new paradigm."
There´s nothing really Rube Goldberg about it, all solid fuelled reactors have this tradeoff between running longer (economics) and running with high neutron efficiency (no poison, but run shorter batches with more refuelling). Running the reactor with higher burnup is better for fuel efficiency, so if you need to add some poison the effect may still be positive on fissile consumption.

Most of today´s reactors operate with some burnable poison. CANDUs don´t have to because of the low burnup and online fuel shuffeling-refuelling.

Liquid fuelled reactors of course have many fewer issues here, they can add fuel online as required.
Liquid fuel... the new paradigm.

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PostPosted: Nov 10, 2012 10:06 am 
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The other effect of using higher initial enrichment together with burnable poisons in a solid fuel reactor is that you create more depleted uranium and less spent fuel.


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PostPosted: Nov 10, 2012 5:04 pm 
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The use of poison may not be Rube Goldberg,
but the rest of the plant is.

This thing has gotten preposterously complicated.
If we ever needed an argument for moving fuel around with a pump,
this design is it.


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PostPosted: Nov 11, 2012 4:43 am 
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Cyril R wrote:
KitemanSA wrote:
Wow. I can't help thinking "Rube Goldberg".

I got to the part where it was discussing the fuel plates and it said to include particles of poison. I couldn't help thinking, "if you have to poison your own reactor, maybe you need a new paradigm."


There´s nothing really Rube Goldberg about it, all solid fuelled reactors have this tradeoff between running longer (economics) and running with high neutron efficiency (no poison, but run shorter batches with more refuelling). Running the reactor with higher burnup is better for fuel efficiency, so if you need to add some poison the effect may still be positive on fissile consumption.

Most of today´s reactors operate with some burnable poison. CANDUs don´t have to because of the low burnup and online fuel shuffeling-refuelling.

Liquid fuelled reactors of course have many fewer issues here, they can add fuel online as required.

Thorium can act as a neutron 'Bank'. It will accept deposit of neutrons into a 'U-233 account'. Later, when the losses of neutrons to fission products like Samarium become too much, the U-233 will be able to supplement the fissile part of the fuel. The result is a high burn up of the total fuel, including part of thorium converted to U-233.
This is taken to its logical conclusion in the Indian document
http://www.dae.nic.in/writereaddata/.pdf_38
The document deals with existing solid fuel reactors but the concept could be applied to all the reactors.


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PostPosted: Nov 11, 2012 6:54 am 
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djw1 wrote:
The use of poison may not be Rube Goldberg,
but the rest of the plant is.

This thing has gotten preposterously complicated.
If we ever needed an argument for moving fuel around with a pump,
this design is it.


I don´t see it. The fuel handling isn´t too complicated. A LFTR would have the fuel processing equipment which is not any less complicated than AHTR fuel handling.

One can easily argue the opposite. Moving fuel with the pump means more demands on materials, heat exchanger compactness, shielding, maintenance that can get complicated. Of course it´s not entirely fair as the AHTR would be an open cycle whereas the LFTR would achieve a closed cycle.

As I´ve argued before, much of the work done for the AHTR is directly transferable to LFTRs. Pumps, heat exchangers, materials, coolant chemistry control, a long list of stuff that is transferable to LFTRs almost verbatim. If AHTRs are built first, then there´s also a market development that can similarly be used to build LFTRs. Having a big market for things like beryllium, lithium7, Hastelloy N, carbon/carbon and SiC composites, 20% LEU fuel, etc. this is a really good thing for LFTR development.


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PostPosted: Nov 11, 2012 7:34 am 
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Cyril R wrote:
Having a big market for things like beryllium, lithium7, Hastelloy N, carbon/carbon and SiC composites, 20% LEU fuel, etc. this is a really good thing for LFTR development.
True, but can you say "technology lock-in"?

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PostPosted: Nov 11, 2012 7:56 am 
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Fuel handling not too complicated???

The two IVFHMs pick up assemblies using a
complicated grappling mechanism,
somehow hand off to two double handed ARMS,
which handoff to the UFTM which goes to a little train
which ...

It takes about 30 dense pages to incompletely describe.
The fault tree on this design is fractal.

My position has always been that near-continuous processing
of hot fuel is not currently technically feasible.
It certainly hasn't been demonstrated.
That's why we should put LFTR on the shelf
and be working on the DMSR.

Jack


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PostPosted: Nov 11, 2012 8:53 am 
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djw1 wrote:
Fuel handling not too complicated???

The two IVFHMs pick up assemblies using a
complicated grappling mechanism,
somehow hand off to two double handed ARMS,
which handoff to the UFTM which goes to a little train
which ...

It takes about 30 dense pages to incompletely describe.
The fault tree on this design is fractal.

My position has always been that near-continuous processing
of hot fuel is not currently technically feasible.
It certainly hasn't been demonstrated.
That's why we should put LFTR on the shelf
and be working on the DMSR.

Jack


It´s not more complicated than CANDU refuelling. But I agree that this is a weak spot in their design and can be much simpler, with a single grappler on overhead crane that inserts the spent fuel elements in the buffer salt (this design doesn´t use buffer salt though).

A DMSR is a great way to get started on MSRs I agree, but they are not as simple as you think. There´s the offgas processing system, which makes 20,000 kWt for a GWe reactor. It is rapid continuous processing that you can´t avoid even without fissile processing. There will need to be valves for pressure swing operation of the offgas tanks. Then there will be a noble metal plateout filter module, which may need replacement, which needs robot arms and cutting or bolting tools. Then there is graphite replacement, which will need grapplers and arms and such. There will be flush tanks and fuel holdup tanks or dump tanks, there will be radioactive activated secondary coolant, etc. There will be 3 heat exchange loops as compared to just one in a BWR, there will have to be systems to suppress the pressure from failed steam generator tubing. There will be fuel addition systems, double containments to deal with the intensely radioactive primary loop, etc. Once you get into detailed design it´s not simple anymore.

As much as I like MSRs I don´t see how any of them scores well on simplicity.


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PostPosted: Nov 11, 2012 9:11 am 
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djw1 wrote:
My position has always been that near-continuous processing of hot fuel is not currently technically feasible. It certainly hasn't been demonstrated. That's why we should put LFTR on the shelf and be working on the DMSR.
Except, as I understand it, the fuel reprocessing will be by one fairly simple process, fluoride volatility, and one of the simplest processes known to man, fractional distillation.

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PostPosted: Nov 11, 2012 11:40 am 
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I agree that there is a lot of useful stuff in the AHTR effort,

I agree that moderator/PHX internals change out etc are formidable problems facing the DMSR.

I simply want to solve these problems before we get into all the additional issues
of trying to create a breeder.

I also agree that the offgas system has to be done very carefully.
But I dont understand the requirement for pressure swing.
What azeotropes are we trying to separate?
This is a real question, not a rhetorical flourish.

Jack


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PostPosted: Nov 11, 2012 12:00 pm 
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http://en.wikipedia.org/wiki/Fluoride_volatility
With fluoride volatility you get Pu,U,Np boiling at pretty similar temperatures so I'm guessing that they will travel together. But you also have Mo, Tc, Br in the same neighborhood so likely the separation of these from the actinides will be poor from straight fluoridation and then fractional distilling of the gases.

The metals Mo, and Tc want to come out of the salt and will tend to plate out on any cool metal surface where the salt flow is slower. One such area is the inside of the heat exchanger - which is not a convenient place for us as this creates decay heat problems inside the HX in some accident scenarios. But it seems to me that we could have a deliberate place for the noble metals to place out that would be even more attractive than the HX (lower salt flow rates).

Another approach is to use vacuum distillation. With this you get Li, and Be but you also will get Zr and Cs. I think we also will get UF4 - but this should be verified. This is a good way to quickly recycle the FLiBe and possibly most of the uranium. This could be the first step in processing and it will quickly remove the valuable parts of the fuel salt and return them to active duty. The remainder can sit and cool for a while before we undertake the fluoridation step.


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PostPosted: Nov 11, 2012 12:26 pm 
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djw1 wrote:
But I dont understand the requirement for pressure swing.
What azeotropes are we trying to separate?


No azeotropes, but a charge/discharge necessity. The noble gasses are krypton and xenon. The xenon 137 will decay to cesium 137. That then sticks in the tank. Next, we want to wait a while so that most of the xenon 137 has decayed, and then discharge the tank of remaining noble gas krypton-xenon, which can be stored in high pressure cylinders. Since new xenon 137 will be produced in the reactor continuously, we need a second tank to take that fresh noble gas. So we need two tanks and a valve.


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PostPosted: Nov 11, 2012 3:09 pm 
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With proper packing and offgas tank(s) design,
we should be able to get close enough to plug flow
so switching tanks is not necessary.
I think this was ORNL's intention.


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