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PostPosted: Mar 03, 2014 11:43 pm 
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ondrejch wrote:
Version 1.0.1 of the TAP whitepaper: http://transatomicpower.com/white_paper ... _Paper.pdf

Thanks Ondrej.
The two new Addenda are quite interesting.
Especially this last bit:
Quote:
By combining a moderated driver region with an unmoderated blanket region, TAP reactors achieve conversion ratios above 0.9 and still maintain criticality, enabling up to 96% burnup for clean and complete fuel consumption.

This is going in the right direction for an optimum bi-modal spectrum reactor.
But the core-blanket geometry has its limitations.
More generally, the solution is a lattice of fast/thermal regions, the most obvious incarnation of which is a lattice of fat fuel channels with low surface-to-volume ratio, set well apart from each other in a matrix of pure moderator - preferably with much better performance than ZrH inside Hastelloy tubes.
Sounds strangely familiar....


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PostPosted: Mar 04, 2014 12:18 am 
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Wouldn't you rather reverse the arrangements with some boiling water channels moderating neutrons for close-by areas and fast neutrons proceeding further away?
Gases can leave the liquid, or be made to, but Samarium and the likes may still have to be crystallized out from the liquid salt.


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PostPosted: Mar 05, 2014 7:52 am 
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Nice presentation by Leslie Dewan at http://www.nei.org/CorporateSite/media/ ... MR2014.pdf

Is moderation better with LiF than FLiBe? Is this part of the design success?


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PostPosted: Mar 05, 2014 10:34 am 
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Neither design relies on the salts for much moderation. The Transatomic design plans to use clad zirconium hydride, whose chemical stability in the reactor operating environment is very questionable, while Flibe Energy plans to use graphite for a moderator material.


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PostPosted: Mar 05, 2014 11:43 am 
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robert.hargraves wrote:
Nice presentation by Leslie Dewan at http://www.nei.org/CorporateSite/media/ ... MR2014.pdf

Is moderation better with LiF than FLiBe? Is this part of the design success?


The moderation difference between these two is minor. Be has the advantage that when it absorbs a neutron it often splits and emits two neutrons so that it actually (very slightly) helps the neutron economy. Adding Be also lowers the melting temperature of the fuel salt so it works better for designs that are trying to stay under 704C. But Be has the disadvantage that it has to be treated as a toxin so there are some additional handling costs when creating the fresh fuel salt. Personally, I don't see any additional costs once the reactor starts up since then you have deadly hot (700C), deadly radioactive fuel salt that drives the handling and protection requirements so whether the fuel salt contains Be or not I don't think changes anything.


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PostPosted: Mar 05, 2014 11:46 am 
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Since Hastelloy N is only rated up to 700 C, with 650 C considered a more reasonable upper temperature range, lowering the melting point of the salts used in the reactor is important, and beryllium is essential for doing this in a neutronically-responsible way.


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PostPosted: Mar 05, 2014 11:47 am 
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If we have lithium and beryllium falling to pieces in the reactor though you will have to add more continuously during the reactor life.


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PostPosted: Mar 05, 2014 12:39 pm 
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Yes you need to add tiny bits of Li and Be through the life of the reactor to keep the quantity of each constant. I'm not sure that the tiny bit we consume over the life of a reactor will be enough to require any compensation. However, since it is a liquid fuel making these adjustments is a minor task.


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PostPosted: Mar 05, 2014 9:59 pm 
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The Hastelloy N data sheet seems to indicate it's useable in fluoride salts up to 871C.
http://www.haynesintl.com/pdf/h2052.pdf

Since TAP mentions in their white paper the potential for swapping out the moderator rods every 4 years (due to neutron damage) could they be intending to just use thin Hastelloy N for cladding of the moderator?

I must admit their proposal brings some favorable features, especially with respect to waste burning that will help get them support politically and from the general public. PR seems to be a major problem with any type of nuclear technology campaign in the public eye.

They certainly seem to have done their homework and I would hesitate to disparage their work or have a knee jerk NIH reaction. I doubt they made any obvious mistakes or oversights at this point given the oversight. Maybe at best overly optimistic estimates? I've found it best when presented with alternative methods or designs to first try your best to make them workable before critiquing them. It helps to clarify both the strengths and weaknesses, sift the wheat from the chaff.

Any money going into Molten Salt research is going to help the entire field. Nuclear needs all the good PR and press it can get.


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PostPosted: Mar 05, 2014 10:16 pm 
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randomly wrote:
could they be intending to just use thin Hastelloy N for cladding of the moderator?
It had better be thin, because Hastelloy absorbs neutrons like a dry sponge in water.
It's probably the main reason why their neutronics calcs yield a CR of only 0.9


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PostPosted: Mar 07, 2014 2:51 am 
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Yes, as mentioned before, they use "--" for cladding.

A major red flag. Not just in terms of breeding ratio, also in terms of radiation and chemical resistance. Hastelloy N will not last long in the middle of a nuclear reactor. It will also be embrittled by the partial pressure of hydrogen atmosphere that will form at equilibrium operation. There are very few materials that will work, even tough advanced stuff like silicon carbide is attacked by hot hydrogen.


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PostPosted: Mar 07, 2014 3:51 am 
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Water in tubes as moderator-coolant could possibly work better. As a negative, it introduces high pressure water/steam in the core. That is only an engineering challenge.


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PostPosted: Mar 11, 2014 4:47 pm 
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For me there are a few questions about the TAP paper

Fuel Composition

I did not find proper data on their (TAP) fuel composition and its properties.Where can I find it?

Freeze Valves

Many MSR concepts include freeze valves for the fuel. In the TAP white paper it is mentioned a couple of times. In a power reactor there is a certain fraction of fission products in the fuel that creates an awful lot of heat. That means that a very strong cooling is required to close it. The max. diameter of the pipe is limited. The decay heat is reduces during operation in the frozen fuel due to decay. After a certain time it requires more and more time to open it. Did anyone calculate a freeze valve for a power MSR beside of the ORNL 4541?

Fuel Treatment

A main challenge for any MSR concept is the fuel treatment. Fission products generate a couple of kW during the 1st day after fission. I did not find detailled information about the fuel treatment of the TAP concept. A conventional reprocessing unit working with the PUREX process was estimated to 16 billion $ by AREVA 2006 for the US. How much did they estimate for the reprocessing?

Cost Estimate

Is there any detailled estimate on the TAP concept costs?


Last edited by HolgerNarrog on Mar 12, 2014 3:39 pm, edited 2 times in total.

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PostPosted: Mar 12, 2014 5:27 am 
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The crux of burning the used fuel has to be a low cost removal of fission product neutron poisons.
Molten salt approach means that Xe, Kr and other volatile fractions can be easily removed. That leaves Samarium as the other major poison. Fractional crystallization could be the cleanest method not involving other solvents.
Otherwise, the uranium can be removed by chloride/fluoride volatility. Plutonium and TRU's can be separated by electrolysis as in IFR processing.
Recovered plutonium can provide the desired enrichment equivalent or fissile fuel.
Water in pressure tubes, if acceptable, will be a surer way to provide moderator than Zirconium Hydride.


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PostPosted: Mar 12, 2014 3:48 pm 
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Dear Jagdish....

the TAP WAMSR concept ist based partly on a thermal or semi-thermal neutron spectrum. In opposite to the todays fast MSR concepts many fission products will disturb.

In the French MSFR concept the fuel reprocessing is studied intensifly...INP Grenoble ..LE REACTEUR A SELS FONDUS MSFR... It requires plenty of repetitions to achieve the required accuracy of separation. I would assume that the fuel processing itself will probably costs more than the mentioned 2 bn$.


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