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PostPosted: Feb 24, 2014 7:50 pm 
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I have a couple of comments about the TAP white paper..

Firstly I think Transatomic should be congratulated on producing a highly innovative design which makes a serious attempt at moving the whole MSR debate forward, especially in the context of simultaneously addressing nuclear waste incineration and base-load electricity generation.

Playing devil's advocate for a moment, is there a way to take the best elements of the three most promising approaches (eg, Transatomic / Flibe / Terrestrial Energy) to create a sweet-spot design we can all agree on.

Just as an example, would there be any cost / safety / reliability advantage in exploiting the TAP fuel salt / moderator combination with the TEI "Integrated" denatured MSR approach. Such a reactor would help TAP avoid the need for the fuel circuit to leave the reactor vessel and also eliminate concerns about the a primary circuit freezing up (potentially important given the higher melting point).

Again just thinking out loud, would there be any advantages to creating a "Sandwich" core design with repeating layers of fuel salt-coolant-moderator-coolant-fuel salt (etc). If the moderator layer was sandwiched between two coolant layers, this might help to keep hydrogen embrittlement localized to the moderator (jam) layers, which could be removed periodically for inspection.

Apologies in advance if these are naive questions.. cheers RB


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PostPosted: Feb 24, 2014 8:59 pm 
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There's no indication that Transatomic has a viable moderator material, so there's little there to hybridize with other approaches.


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PostPosted: Feb 24, 2014 9:32 pm 
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RussB wrote:
is there a way to take the best elements of the three most promising approaches (eg, Transatomic / Flibe / Terrestrial Energy) to create a sweet-spot design we can all agree on.

We have seen some info on the approaches of the first and the last, but nothing from the one in the middle. What are their "elements" ?


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PostPosted: Feb 24, 2014 9:58 pm 
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jaro wrote:
RussB wrote:
is there a way to take the best elements of the three most promising approaches (eg, Transatomic / Flibe / Terrestrial Energy) to create a sweet-spot design we can all agree on.

We have seen some info on the approaches of the first and the last, but nothing from the one in the middle. What are their "elements" ?


Have you watched any of the presentations that I have given and posted online? Fluids, processing, and structural materials are all disclosed. No surprises there. But this thread is about Transatomic's design, not Flibe's.


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PostPosted: Feb 26, 2014 10:26 pm 
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RussB wrote:
is there a way to take the best elements of the three most promising approaches (eg, Transatomic / Flibe / Terrestrial Energy) to create a sweet-spot design we can all agree on.

Looking at what's been published so far by "the three most promising approaches," it's hard to judge what "the best elements" are, "to create a sweet-spot design we can all agree on."

In terms of reactor design and plant arrangement, Transatomic's and Terrestrial Energy's concepts show some level of detail that might be useful in picking a sweet-spot.

In terms of colorful slide illustration, Flibe is obviously the best.

So it seems we might want some sort of combination of Transatomic's and Terrestrial Energy's concepts -- with a generous splash of colors from Flibe.


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PostPosted: Feb 27, 2014 2:18 am 
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All solid moderators including graphite suffer from Wigner effect. It may be worthwhile to go back to stolid old water/heavy water. Some soluble moderator like BeF2 in solution could be tried.
Jaro's HW MSR is one possibility. A BWR with fuel in tubes is another. The fuel could circulate through a re processor where Xe, Kr are removed as gases. SmF3 (and other lanthanides crystallized at the same time) are removed by fractional crystallization.
Solid metallic thorium is used for reactivity stabilization.


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PostPosted: Feb 27, 2014 5:28 pm 
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Only cold graphite suffers from Wigner energy build up. Hot graphite releases the energy.


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PostPosted: Feb 28, 2014 5:30 am 
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Lars wrote:
Only cold graphite suffers from Wigner energy build up. Hot graphite releases the energy.


But hot graphite swells and eventually damages itself in a neutron flux. Different damage process (no accumulated but in stead released energy in the matrix itself), but still damage.

Lower temperature Wigner energy can be annealed out but requires higher and higher annealing temperatures each consecutive annealing run. I wonder if something similar is the case with annealing the higher temperature swelling damage. If so there will be a limited number of "recycles" the graphite in a MSR will last.


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PostPosted: Feb 28, 2014 9:21 pm 
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I had a few emails with ORNL's graphite expert. He left me with the impression re-annealing the graphite would be more complicated than simply heating it up. But it seems like this is a little explored area. Both Sr90 and Cs137 have gas precursors so we should presume that even after scraping the surface the graphite is still radioactive for several hundred years. I would guess that the heat production though would be pretty modest so that cooling isn't an issue for disposal.


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PostPosted: Mar 01, 2014 3:26 am 
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The ORNL work on graphite indicates that the graphitization temperature is crucial. The higher it is the lower the swelling. It may be that heating up graphite out of flux anneals the damage and even restores most of the original volume, but likely the performance in the irradiation after that will not be the same. Maybe faster swelling. So likely we'll have to grind up the graphite and re-graphitize at very high temperature (like a 3000K).

Removing the radionuclides should be doable. Heating up in a hard vacuum will vaporize all the fission products (even strontium fluoride). Then what you need is a recirculating filter in the vacuum oven to condense and remove these particles.


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PostPosted: Mar 02, 2014 2:20 am 
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If we are reusing the graphite then removing the deeply embedded fission products isn't required. At least I expect the quantity of deeply embedded stuff to be small enough to not be an issue.


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PostPosted: Mar 02, 2014 5:24 am 
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Lars wrote:
If we are reusing the graphite then removing the deeply embedded fission products isn't required. At least I expect the quantity of deeply embedded stuff to be small enough to not be an issue.


Yes, and removing them should be part of any thermal graphitization process anyway.

Will it be feasible to regenerate the graphite logs in their fabricated form, so as to produce a regenerated log/sphere/plank of graphite? Or will the high temperatures needed to fully regenerate the graphite result in cracking? Or just insufficient strength. Do we even know if the original volume is restored with sufficient heating? If we don't have to grind up the unbroken elements then recycling becomes a lot more interesting, best case would be that most elements can be re-used several times or more.


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PostPosted: Mar 02, 2014 7:14 am 
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I imagine the logs would have to be broken up, but I am not sure you would actually have to powder them all.

You might just be able to break it up into 'gravel' and then regraphitise it with filling material.


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PostPosted: Mar 02, 2014 9:40 am 
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Back on topic. There's plenty of threads to talk about graphite. This isn't one of them.


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PostPosted: Mar 03, 2014 9:57 pm 
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Version 1.0.1 of the TAP whitepaper: http://transatomicpower.com/white_paper ... _Paper.pdf


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